View source for Metrication

{{Short description|Conversion to the metric system of measurement}}
{{Use dmy dates|date=November 2023|cs1-dates=ll}}
{{Use British English|date=November 2023}}
[[File:Metrication by year map.svg|thumb|upright=1.35|World map, colour-coded to show the years the countries started the process of official conversion to the metric system. Using data from PhD thesis by Hector Vera and NIST.]]
'''Metrication''' or '''metrification''' is the act or process of converting to the [[metric system]] of measurement.<ref>{{OED|Metrication}}</ref> All over the world, countries have transitioned from local and traditional [[Unit of measurement|units of measurement]] to the metric system. This process began in [[French Revolution|France during the 1790s]], and has persistently advanced over two centuries, accumulating into 95% of the world officially exclusively using the [[International System of Units|modern metric system]].<ref name=":9">{{cite thesis |id={{ProQuest|924487292}} |last1=Vera |first1=Hector |date=2012 |title=The Social Life of Measures Metrication in the United States and Mexico, 1789–2004 |at= p. 49, ch 2}}</ref> Nonetheless, this also highlights that certain countries and sectors are either still transitioning or have chosen not to fully adopt the metric system.

== Overview ==

The process of metrication is typically initiated and overseen by a country's government, generally motivated by the necessity of establishing a uniform measurement system for effective international cooperation in fields like trade and science. Governments achieve metrication through either mandatory changes to existing units within a specified timeframe or through voluntary adoption.{{citation needed| date = May 2025 }}

While metric use is mandatory in some countries and voluntary in others, all countries have recognised and adopted the SI, albeit to different degrees, including the United States. As of 2011, ninety-five percent of the world's population live in countries where the metric system is the only legal system of measurement.<ref name="Vera2011">{{cite thesis |id={{ProQuest|924487292}} |last1=Vera |first1=Hector |date=2012 |title=The Social Life of Measures Metrication in the United States and Mexico, 1789–2004}}</ref>{{rp | at=p. 49, ch 2}}

According to the [[National Institute of Standards and Technology|National Institute of Standards and Technology (NIST)]], there are only three countries that do not have mandatory metric laws ([[Liberia]], [[Myanmar]], and the [[United States]]),<ref>{{Cite journal |date=2023-08-28 |title=U.S. Metrication Frequently Asked Questions (FAQs) |url=https://www.nist.gov/pml/owm/metric-si/us-metrication-frequently-asked-questions-faqs |journal=NIST |language=en |quote=In 1971, the National Bureau of Standards (NBS, now NIST) published the combined reports of the U.S. Metric Study,  which also contained a map depicting a list of countries 'uncommitted' to mandatory metrication (Figure 2). The U.S. and other countries listed were described as 'Islands in a Metric World.' The flaw with this perspective was that the concept didn't recognize that the U.S. had been 'metric' since 1866, when the metric system was first legalized. A few years after the U.S. Metric Study was published, Congress passed the Metric Conversion Act adopting voluntary metrication that was signed into law by President Ford in 1975. Over time, various versions of the map/country list became integrated into even more metrication publications. The Central Intelligence Agency (CIA) Factbook is one of the often cited sources of the U.S./Liberia/Burma metric myth. The first unclassified version of the CIA Factbook was published around the same time the U.S. Metric Study. It's likely that the original list of 'uncommitted' countries was incorporated, then edited as countries adopted mandatory metric laws. Over the years, many web resources have quoted the CIA Factbook, perpetuating the metric myth and elevating the map to a pop culture meme. The U.S. metrication status is best described as a Metric Continuum.}}</ref><ref>{{Cite journal |last=Benham |first=Elizabeth |date=2020-10-06 |title=Busting Myths about the Metric System |url=https://www.nist.gov/blogs/taking-measure/busting-myths-about-metric-system |journal=NIST |language=en}}</ref> however a research paper completed by Vera (2011) stated in practice there were four additional countries, namely the [[Compact of Free Association|United States COFA]] countries ([[Federated States of Micronesia]], [[Marshall Islands]] and [[Palau]]), and [[Samoa]].<ref name="Vera2011" />{{rp||pages=60, 494–496}}[[Samoa]] has since mandated metric trade.<ref>{{Cite web |title=Metrology – Ministry of Commerce, Industry and Labour |url=https://www.mcil.gov.ws/?page_id=5087 |archive-url=https://web.archive.org/web/20241225163521/https://www.mcil.gov.ws/?page_id=5087 |archive-date=2024-12-25 |access-date=2025-11-16 |website=www.mcil.gov.ws |language=en-US}}</ref>

In 2018, the Liberian government had pledged to adopt the metric system.<ref name="tlo_20180525">{{Cite web |last=Dopoe |first=Robin |url=https://www.liberianobserver.com/business/govt-pledges-commitment-to-adopt-metric-system/ |title=Gov't Pledges Commitment to Adopt Metric System |publisher=Liberian Observer Corporation |work=The Observer |date=25 May 2018 |access-date=8 December 2018 |archive-date=9 November 2020 |archive-url=https://web.archive.org/web/20201109004653/https://www.liberianobserver.com/business/govt-pledges-commitment-to-adopt-metric-system/ |url-status=dead}}</ref>  In 2013, the Myanmar Ministry of Commerce announced that Myanmar was preparing to adopt the metric system as the country's official system of measurement, and [[Myanmar units of measurement#Adoption of SI (metric) system|metrication in Myanmar]] began with some progress was made (road signs and temperature are legislated to be in metric), however there had been very little progress in local trade.<ref>{{cite web|last=Kohler|first=Nicholas|date=3 March 2014|title=Metrication in Myanmar|url=http://archive-3.mizzima.com/opinion/features/item/10955-metrication-in-myanmar/10955-metrication-in-myanmar|url-status=dead|archive-url=https://web.archive.org/web/20170818172934/http://archive-3.mizzima.com/opinion/features/item/10955-metrication-in-myanmar/10955-metrication-in-myanmar|archive-date=18 August 2017|access-date=18 August 2021|website=Mizzima}}</ref><ref>{{Cite news|date=10 October 2013|title=Myanmar to Adopt Metric System|work=Eleven|url=http://elevenmyanmar.com/index.php?option=com_content&view=article&id=3684:myanmar-to-adopt-metric-system&catid=44:national&Itemid=384|url-status=dead|archive-url=https://web.archive.org/web/20140210092143/http://elevenmyanmar.com/index.php?option=com_content&view=article&id=3684:myanmar-to-adopt-metric-system&catid=44:national&Itemid=384|archive-date=10 February 2014}}</ref> 

{{As of|2023}}, the United States has a national policy of adopting the metric system based on the [[Metric Conversion Act]] of 1975, amended by the Omnibus Trade and Competitiveness Act of 1988, and Presidential Executive Order 12770 of 1991, and all [[United States government]] agencies are required to adopt it.<ref>{{Cite web |website=NIST |date=5 February 2015 |title=Metric (SI) Program |url=https://www.nist.gov/pml/owm/metric-si |access-date=14 November 2023 |archive-date=28 November 2023 |archive-url=https://web.archive.org/web/20231128043131/https://www.nist.gov/pml/owm/metric-si |url-status=live }}</ref>

The metrication process can take years to implement and complete: for instance, [[Guyana]] adopted the metric system in 2002 and was only able to make it mandatory in local trade 2017 after the metric system was fully adopted in schools.<ref>{{Cite web |title=Metrification plan to be implemented in all 10 regions – GNBS |url=https://guyanachronicle.com/2017/06/25/metrification-plan-to-be-implemented-in-all-10-regions-gnbs/ |access-date=15 November 2023 |website=Guyana Chronicle|date=25 June 2017 }}</ref> [[Antigua and Barbuda]], also officially metric, is moving slowly in its metrication process, with a new push in 2011 for all government agencies to convert by 2013 and the entire country to use the metric system by the first quarter of 2015.<ref name="anb">{{cite news|title=Finance minister outlines metrication plans, goals and timetable|url=http://www.antiguaobserver.com/finance-minister-outlines-metrication-plans-goals-and-timetable/|access-date=12 November 2011|work=Antigua Observer|date=18 October 2011|archive-date=10 January 2014|archive-url=https://web.archive.org/web/20140110163640/http://www.antiguaobserver.com/finance-minister-outlines-metrication-plans-goals-and-timetable/|url-status=dead}}</ref> Other metric [[Caribbean]] countries, such as [[Saint Lucia]] officially metric 2000,  are still in the process toward full conversion.<ref>{{cite news |url = http://www.jamaicaobserver.com/news/html/20050322T200000-0500_77361_OBS_ST_LUCIA_BEGINS_DRIVE_TO_IMPLEMENT_METRIC_SYSTEM_TO_CATCH_UP_WITH_REGION.asp |title=St Lucia begins drive to implement metric system to catch up with region |agency=Associated Press |year=2005 |newspaper=The Jamaica Observer |access-date=5 November 2007 |archive-url=https://web.archive.org/web/20071018000003/http://jamaicaobserver.com/news/html/20050322T200000-0500_77361_OBS_ST_LUCIA_BEGINS_DRIVE_TO_IMPLEMENT_METRIC_SYSTEM_TO_CATCH_UP_WITH_REGION.asp |archive-date = 18 October 2007 |url-status=dead}}</ref>

The [[United Kingdom]] has officially embraced a dual measurement system. The United Kingdom as of 2007 halted [[Metrication in the United Kingdom|its metrication process]], and retain imperial units of the mile and yard in road markings, [[pint]]s for returnable milk containers, and (with Ireland) for the pint for draught beer and cider sold in pubs.<ref name="Weights and measures: the law">{{Cite web |title=Weights and measures: the law |url=https://www.gov.uk/weights-measures-and-packaging-the-law |access-date=2023-11-15 |website=GOV.UK |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030170848/https://www.gov.uk/weights-measures-and-packaging-the-law |url-status=live }}</ref> Throughout the 1990s, the [[European Commission]] helped accelerate the metrication process for member states, for the implemented the [[European units of measurement directives|Units of Measure Directive]] to promote trade. This acceleration caused public backlash in the United Kingdom, and in 2007 the United Kingdom announced that it had secured permanent exemptions listed above and, to appease British public opinion and to facilitate trade with the United States, the option to include imperials units alongside metric units could continue indefinitely.<ref name="Weights and measures: the law"/><ref name="EUGivesUp">{{cite news |date=11 September 2007 |title=EU gives up on 'metric Britain |work=BBC News |url=https://news.bbc.co.uk/2/hi/uk_news/6988521.stm |access-date=23 May 2009 |archive-date=17 February 2009 |archive-url=https://web.archive.org/web/20090217214248/http://news.bbc.co.uk/1/hi/uk/6988521.stm |url-status=live }}</ref>

The United Kingdom and the United States face ongoing resistance toward metrication, which may be partially rooted in a belief that their cultural identity is intertwined with the traditional measurement systems they historically have used.<ref>{{Cite web |last=Vincent |first=James |date=16 January 2023 |title=The battle of the standards: why the US and UK can't stop fighting the metric system |url=https://www.theverge.com/2023/1/16/23507199/us-uk-anti-metric-sentiment-beyond-measure-james-vincent-excerpt |access-date=15 November 2023 |website=The Verge}}</ref> This has resulted in a review of mandatory sales and trade of metric units by the UK government. The outcome of this review with over 100&nbsp;000 respondents was that a majority had limited or no appetite for increased use of imperial measures.<ref>{{Cite web |date=3 June 2022 |title=Choice on units of measurement: markings and sales |url=https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales |access-date=15 November 2023 |website=GOV.UK |archive-date=7 November 2023 |archive-url=https://web.archive.org/web/20231107040700/https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales |url-status=live }}</ref>

== Forerunners of metrication ==
[[File:Metric system French adoption decree (1795).jpg |thumb|upright=1.2| National Convention decree of April 1795 establishing the metric system]]

The metre was adopted as exclusive measure in 1801 under the [[French Consulate]], then the [[First French Empire]] until 1812, when [[Napoleon]] decreed the introduction of the ''[[mesures usuelles]]'' which remained in use in France up to 1840 in the reign of [[Louis Philippe I|Louis Philippe]].<ref>{{Cite book|last=Larousse|first=Pierre (1817-1875) Auteur du texte|url=https://gallica.bnf.fr/ark:/12148/bpt6k205363w|title=Grand dictionnaire universel du XIXe siècle : français, historique, géographique, mythologique, bibliographique.... T. 11 MEMO-O / par M. Pierre Larousse|date=1866–1877|pages=163|access-date=22 December 2021|archive-date=22 December 2021|archive-url=https://web.archive.org/web/20211222110248/https://gallica.bnf.fr/ark:/12148/bpt6k205363w|url-status=live}}</ref> Meanwhile, the metre was adopted by the Republic of Geneva.<ref name=":5" /> After the joining of [[canton of Geneva]] to Switzerland in 1815, [[Guillaume Henri Dufour]] published the first Swiss official map for which the metre was adopted as unit of length.<ref name=":6" /><ref name=":7" /> A Swiss-French binational officer, [[Napoleon III|Louis Napoléon Bonaparte]] was present when a baseline was measured near [[Zürich]] for [[Topographic Map of Switzerland|Dufour map]] which would win the gold medal for the national map at the [[Exposition Universelle (1855)|Exposition Universelle of 1855]].<ref>{{Cite book|last=Durand|first=Roger|url=https://books.google.com/books?id=7-8LnQ9iF04C|title=Guillaume-Henri Dufour dans son Temps 1787-1875|date=1991|publisher=Librairie Droz|isbn=978-2-600-05069-2|pages=145|language=fr}}</ref><ref>{{Cite web|title=Napoleon III.|url=https://hls-dhs-dss.ch/articles/023316/2010-11-02/|access-date=22 December 2021|website=hls-dhs-dss.ch|language=de|archive-date=14 December 2021|archive-url=https://web.archive.org/web/20211214074352/https://hls-dhs-dss.ch/articles/023316/2010-11-02/|url-status=live}}</ref><ref>{{Cite web|date=14 July 2019|title=Henri Dufour et la carte de la Suisse|url=https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/|access-date=22 December 2021|website=Musée national - Blog sur l'histoire suisse|language=fr-FR|archive-date=8 January 2022|archive-url=https://web.archive.org/web/20220108033346/https://blog.nationalmuseum.ch/fr/2019/07/dufour-le-cartographe/|url-status=live}}</ref> Among the scientific instruments calibrated on the metre, which were displayed at the Exposition Universelle, was [[Jean Brunner|Brunner]] apparatus, a geodetic instrument devised for measuring the central baseline of Spain whose designer, [[Carlos Ibáñez e Ibáñez de Ibero]] would represent Spain at the [[International Statistical Institute]]. In addition to the Exposition Universelle and the second Statistical Congress held in Paris, an International Association for obtaining a uniform decimal system of measures, weights, and coins was created there in 1855.<ref>{{Cite book|last=Quinn|first=T. J|url=|title=From artefacts to atoms: the BIPM and the search for ultimate measurement standards|date=2012|isbn=978-0-19-990991-9|pages=8|publisher=Oxford University Press |oclc=861693071}}</ref><ref>{{Cite book|last=Yates|first=James|url=https://play.google.com/store/books/details?id=mAo_AAAAYAAJ|title=Narrative of the Origin and Formation of the International Association for Obtaining a Uniform Decimal System of Measures, Weights and Coins|date=1856|publisher=Bell and Daldy|access-date=22 December 2021|archive-date=22 December 2021|archive-url=https://web.archive.org/web/20211222125411/https://play.google.com/store/books/details?id=mAo_AAAAYAAJ|url-status=live}}</ref><ref>{{Cite journal|last=Brenni|first=Paolo|date=1996|title=19th Century French Scientific Instrument Makers - XI: The Brunners and Paul Gautier|url=https://www.unav.es/gep/TheBrunnersCartaParis.pdf|journal=Bulletin of the Scientific Instrument Society|volume=49|pages=3–5|via=UNAV|access-date=22 December 2021|archive-date=18 September 2021|archive-url=https://web.archive.org/web/20210918062512/https://www.unav.es/gep/TheBrunnersCartaParis.pdf|url-status=live}}</ref><ref>{{cite journal |last1=Appell |first1=Paul |title=Le centenaire du général Ibañez de Ibéro |journal=Revue internationale de l'enseignement |date=1925 |volume=79 |issue=1 |pages=208–211 |url=https://education.persee.fr/doc/revin_1775-6014_1925_num_79_1_7841 |access-date=22 December 2021 |archive-date=16 December 2021 |archive-url=https://web.archive.org/web/20211216072326/https://education.persee.fr/doc/revin_1775-6014_1925_num_79_1_7841 |url-status=live }}</ref> Copies of the Spanish standard would be made for Egypt, France and Germany.<ref>{{Cite book |last=Tardi |first=Pierre |url=https://gallica.bnf.fr/ark:/12148/bpt6k3355272d |title=Traité de géodésie |date=1934 |pages=25 |author-link=Pierre Tardi |access-date=22 December 2021 |archive-date=18 December 2021 |archive-url=https://web.archive.org/web/20211218101406/https://gallica.bnf.fr/ark:/12148/bpt6k3355272d |url-status=live }}</ref><ref>{{Cite web|last=Zuerich|first=ETH-Bibliothek|title=Procès-verbaux des séances de la commission géodésique suisse|url=https://www.e-periodica.ch//digbib/view?pid=bsn-001%3A1877%3A11%3A%3A853|url-status=dead|access-date=22 December 2021|website=E-Periodica|pages=14, 18|language=fr|archive-date=29 July 2021|archive-url=https://web.archive.org/web/20210729085259/https://www.e-periodica.ch//digbib/view?pid=bsn-001:1877:11::853}}</ref> These standards were compared to each other and with Borda apparatus which was the main reference for measuring all geodetic baselines in France.<ref>{{Cite book|last=texte|first=Ismāʿīl-Afandī Muṣṭafá (1825-1901) Auteur du|url=https://gallica.bnf.fr/ark:/12148/bpt6k62478474|title=Recherche des coefficients de dilatation et étalonnage de l'appareil à mesurer les bases géodésiques appartenant au gouvernement égyptien / par Ismaïl-Effendi-Moustapha, ...|date=1864|access-date=22 December 2021|archive-date=18 December 2021|archive-url=https://web.archive.org/web/20211218101418/https://gallica.bnf.fr/ark:/12148/bpt6k62478474|url-status=live}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=uiwPAAAAQAAJ&q=Exp%C3%A9riences+faites+avec+l'appareil+%C3%A0+mesurer+les+bases+appertant+%C3%A0+la+commission+de+la+carte+d'Espagne|title=Expériences faites avec l'appareil à mesurer les bases appertant à la commission de la carte d'Espagne /: ouvrage publié par ordre de la reine|date=1860|publisher=J. Dumaine|language=fr}}</ref><ref name=":8">{{cite journal |last1=Soler |first1=T. |title=A profile of General Carlos Ibáñez e Ibáñez de Ibero: first president of the International Geodetic Association |journal=Journal of Geodesy |date=10 February 1997 |volume=71 |issue=3 |pages=176–188 |doi=10.1007/s001900050086 |bibcode=1997JGeod..71..176S |s2cid=119447198}}</ref> These comparisons were essential, because of the [[Thermal expansion|expansibility]] of solid materials with raise in temperature. Indeed, one fact had constantly dominated all the fluctuations of ideas on the measurement of geodesic bases: it was the constant concern to accurately assess the temperature of standards in the field; and the determination of this variable, on which depended the length of the instrument of measurement, had always been considered by [[Geodesy|geodesists]] as so difficult and so important that one could almost say that the history of measuring instruments is almost identical with that of the precautions taken to avoid temperature errors.<ref>{{cite journal |last1=Guillaume |first1=Ch.-Ed |title=La mesure rapide des bases géodésiques |journal=Journal de Physique Théorique et Appliquée |date=1906 |volume=5 |issue=1 |pages=242–263 |doi=10.1051/jphystap:019060050024200 |url=https://zenodo.org/record/2007289 |access-date=9 December 2023 |archive-date=6 October 2023 |archive-url=https://web.archive.org/web/20231006212819/https://zenodo.org/record/2007289 |url-status=live }}</ref> In 1867, the second general Conference of the [[International Association of Geodesy|European Arc Measurement]] recommended the adoption of the metre in replacement of the toise. In 1869, the [[Russian Academy of Sciences|Saint Petersburg Academy of Sciences]] sent to the [[French Academy of Sciences]] a report drafted by [[Otto Wilhelm von Struve]], [[Heinrich von Wild]] and [[Moritz von Jacobi]] inviting his French counterpart to undertake joint action with a view to ensuring the universal use of the [[metric system]] in all scientific work.<ref>{{cite journal |last1=Guillaume |first1=Ed. |title=Le Systeme Metrique est-il en Peril? |journal=L'Astronomie |date=1916 |volume=30 |pages=242–249 |bibcode=1916LAstr..30..242G}}</ref> The same year, Napoleon III convened the International Metre Commission which was to meet in Paris in 1870. The [[Franco-Prussian War]] broke out, the [[Second French Empire]] collapsed, but the metre survived.<ref>{{cite book |last1=Boucheron |first1=Patrick |last2=Delalande |first2=Nicolas |last3=Mazel |first3=Florian |last4=Potin |first4=Yann |last5=Singaravélou |first5=Pierre |title=Histoire mondiale de la France |date=2018 |publisher=Éditions Points |isbn=978-2-7578-7442-4 |page=694 |oclc=1057452808}}</ref><ref>{{cite journal |last1=Quinn |first1=Terry |title=Wilhelm Foerster's Role in the Metre Convention of 1875 and in the Early Years of the International Committee for Weights and Measures |journal=Annalen der Physik |date=May 2019 |volume=531 |issue=5 |doi=10.1002/andp.201800355 |bibcode=2019AnP...53100355Q |s2cid=125240402 |doi-access=free}}</ref>

During the nineteenth century the metric system of weights and measures proved a convenient political compromise during the unification processes in the Netherlands, Germany and Italy. In 1814, Portugal became the second country not part of the French Empire to officially adopt the metric system. Spain found it expedient in 1849 to follow the French example and within a decade [[Latin America]] had also adopted the metric system, or had already adopted the system, such as the case of Chile by 1848. There was considerable resistance to metrication in the United Kingdom and in the United States. Despite this, they were actually the first countries in the World to use a metric standard for cartography.<ref name=":2" /><ref name=":3" /><ref>{{Cite book |last=texte |first=Ismāʿīl-Afandī Muṣṭafá (1825-1901) Auteur du |url=https://gallica.bnf.fr/ark:/12148/bpt6k62478474 |title=Recherche des coefficients de dilatation et étalonnage de l'appareil à mesurer les bases géodésiques appartenant au gouvernement égyptien / par Ismaïl-Effendi-Moustapha, ... |date=1864}}</ref><ref name=":8" /><ref>{{Cite news |title=Nomination of the STRUVE GEODETIC ARC for inscription on the WORLD HERITAGE LIST |pages=40, 143–144 |url=https://whc.unesco.org/uploads/nominations/1187.pdf |access-date=7 October 2023 |archive-date=19 October 2015 |archive-url=https://web.archive.org/web/20151019205752/https://whc.unesco.org/uploads/nominations/1187.pdf |url-status=live }}</ref>

=== France (1795–1840) ===
The introduction of the metric system into France in 1795 was done on a district by district basis with Paris being the first district. By modern standards the transition was poorly managed. Although thousands of pamphlets were distributed, the Agency of Weights and Measures who oversaw the introduction underestimated the work involved. Paris alone needed 500,000 metre sticks, yet one month after the metre became the sole legal unit of measure, they only had 25,000 in store.<ref name="Alder">{{cite book |last=Alder |first=Ken |title=The Measure of all Things – The Seven-Year-Odyssey that Transformed the World |publisher=Abacus |year=2002 |isbn=978-0-349-11507-8 |location=London}}</ref>{{rp| 269}} This, combined with the excesses of the Revolution and the high level of illiteracy in 18th century France, made the metric system unpopular.

[[Napoleon]] himself ridiculed the metric system but, as an able administrator, recognised the value of a sound basis for a system of measurement. Under the {{lang|FR|décret impérial du 12 février 1812}} (imperial decree of 12 February 1812), a new system of measure – the {{lang|FR|[[mesures usuelles]]}} ("customary measures") was introduced for use in small retail businesses – all government, legal and similar works still had to use the metric system and the metric system continued to be taught at all levels of education.<ref name="Fevier">
{{cite web
|url = http://www.industrie.gouv.fr/metro/aquoisert/metre.htm
|title = Un historique du mètre
|language = fr
|author = Denis Février
|publisher = {{lang|FR|Ministère de l'Economie, des Finances et de l'Industrie}}
|access-date = 10 March 2011
|archive-date = 28 February 2011
|archive-url = https://web.archive.org/web/20110228185545/http://www.industrie.gouv.fr/metro/aquoisert/metre.htm
|url-status = live
}}</ref> That system reintroduced the names of many units used during the ancient regime, but their values were redefined in terms of metric units. Thus the {{lang|FR|toise}} was defined as being two metres, with six {{lang|FR|pieds}} making up one ''toise'', twelve {{lang|FR|pouces}} making up one ''pied'' and twelve {{lang|FR|lignes}} making up one ''pouce''. Likewise the {{lang|FR|livre}} was defined as being 500&nbsp;g, each ''livre'' comprising sixteen ''once'' and each ''once'' eight ''gros'' and the ''aune'' as 120 centimetres.<ref name="H&H">
{{cite web
|url = https://archive.org/stream/outlinesofevolut00halluoft/outlinesofevolut00halluoft_djvu.txt
|title = Outlines of the evolution of weights and measures and the metric system
|first1 = William
|last1 = Hallock
|first2 = Herbert T
|last2 = Wade
|publisher = The Macmillan Company
|year = 1906
|pages = 66–69
|location = London
}}</ref> This intermediate step eased the transition to a metric-based system.

By the {{lang|FR|Loi du 4 juillet 1837}} (the law of 4 July 1837), [[Louis Philippe I]]  effectively revoked the use of ''mesures usuelles'' by reaffirming the laws of measurement of 1795 and 1799 to be used from 1 May 1840.<ref name="histmet">
{{cite web
| url        = http://www.french-metrology.com/en/history/history-mesurement.asp
| title        = History of measurement
| publisher        = Laboratoire national de métrologie et d'essais (LNE) (Métrologie française)
| access-date        = 6 February 2011
| archive-date        = 25 April 2011
| archive-url        = https://web.archive.org/web/20110425025041/http://www.french-metrology.com/en/history/history-mesurement.asp
| url-status        = dead
}}</ref><ref name="crease">{{cite book |first=Robert P. |last=Crease |title=World in the Balance: The Historical Quest for an Absolute System of Measurement |year=2011 |publisher=W. W. Norton & Company |location= New York & London |isbn=978-0-393-34354-0 |pages=124 & 164}}</ref> However, many units of measure, such as the ''livre'' (for half a kilogram), remained in everyday use for many years,<ref name="crease"/><ref>Crease (2011) refers to: {{cite book |last=Kennelly |first=Arthur E. |title=Vestiges of Pre-metric Weights and Measures Persisting in Metric-system Europe, 1926–27 |location=New York |publisher=Macmillan |year=1928 |page=vii}}</ref> and to a residual extent up to this day.
[[File:Fußmaße1.jpg|upright=0.75|thumb|Conversion table in an 1848 German schoolbook showing the metric equivalent of the foot in use in over two dozen countries, including several German states]]

=== Germany (1810–1877) ===
[[File:Baeyer.jpg|left|thumb|upright=0.75|Johann Jacob Baeyer, founder of the ''[[International Association of Geodesy|Europäische Gradmessung]]''|278x278px]]
[[File:Alter Grenzstein Pontebba 01.jpg|upright=0.75|thumb|Stone marking the [[Austria-Hungary|Austro-Hungarian]]/Italian border at [[Pontebba]] displaying [[myriametre]]s (10&nbsp;km), a unit used in [[Central Europe]] in the 19th century<ref name=Europa1842/>]]
At the outbreak of the French Revolution, much of modern-day Germany and Austria were part of the [[Holy Roman Empire]] which had become a loose federation of kingdoms, principalities, free cities, bishoprics and other fiefdoms, each with its own system of measurement, though in most cases the systems were loosely derived from the [[Carolingian]] system instituted by [[Charlemagne]] a thousand years earlier.

During the Napoleonic era, some of the German states moved to reform their systems of measurement using the prototype metre and kilogram as the basis of the new units. [[Baden]], in 1810, for example, redefined the ''Ruthe'' (rods) as being 3.0&nbsp;m exactly and defined the subunits of the ''Ruthe'' as 1 ''Ruthe'' = 10&nbsp;''Fuß'' (feet) = 100&nbsp;''Zoll'' (inches) = 1,000&nbsp;''Linie'' (lines) = 10,000&nbsp;''Punkt'' (points) (for simplicity at the expense of grammar, these are the singular forms of each name) while the ''Pfund'' was defined as 500&nbsp;g, divided into 30&nbsp;Loth, each of 16.67&nbsp;g.<ref name="Europa1842">{{cite web
|url = http://home.fonline.de/fo0126//geschichte/groessen/mas1.htm
|title = Amtliche Maßeinheiten in Europa 1842
|language = de
|trans-title = Official units of measure in Europe 1842
|access-date = 26 March 2011
|archive-date = 14 October 2011
|archive-url = https://web.archive.org/web/20111014224232/http://home.fonline.de/fo0126//geschichte/groessen/mas1.htm
|url-status = live
}} Text version of Malaisé's book.</ref><ref>
{{cite book
|url = http://home.fonline.de/rs-ebs/geschichte/buch/titel.htm
|title = Theoretisch-practischer Unterricht im Rechnen
|language = de
|trans-title = Theoretical and practical instruction in arithmetic
|author = Ferdinand Malaisé
|place = München
|year = 1842
|pages = 307–322
|access-date = 26 March 2011
|archive-date = 14 October 2011
|archive-url = https://web.archive.org/web/20111014221605/http://home.fonline.de/rs-ebs/geschichte/buch/titel.htm
|url-status = live
}}</ref> [[Bavaria]], in its reform of 1811, trimmed the Bavarian ''Pfund'' from 561.288&nbsp;g to 560&nbsp;g exactly, consisting of 32 ''Loth'', each of 17.5&nbsp;g<ref>
{{cite web
|url = http://www.digitalis.uni-koeln.de/Grebenau/grebenau_index.html
|title = Tabellen zur Umwandlung des bayerischen Masses und Gewichtes in metrisches Maß und Gewicht und umgekehrt
|language = de
|trans-title = Conversion tables for converting between Bavarian units of measure and metric units
|location = Munich
|author = Heinrich Grebenau
|year = 1870
|access-date = 7 March 2011
|archive-date = 22 January 2011
|archive-url = https://web.archive.org/web/20110122043300/http://www.digitalis.uni-koeln.de/Grebenau/grebenau_index.html
|url-status = live
}}</ref> while the [[Prussia]]n ''Pfund'' remained at 467.711&nbsp;g.<ref>
{{cite thesis
|degree= Dr.&nbsp;med.&nbsp;vet
|pages= 14–20
|title= Der Marstall des Schlosses Anholt (16. bis 18. Jahrhundert) – Quellen und Materialien zur Geschichte der Pferdehaltung im Münsterland
|trans-title= The stables of the castle Anholt (16th to 18th century) – sources and materials on the history of horses in Munster
|language= de
|url= http://elib.tiho-hannover.de/dissertations/parrass_ss06.pdf
|author= Silke Parras
|year= 2006
|publisher= Tierärztliche Hochschule Hannover [Hannover veterinary university]
|access-date= 7 March 2011
|archive-date= 19 July 2011
|archive-url= https://web.archive.org/web/20110719093650/http://elib.tiho-hannover.de/dissertations/parrass_ss06.pdf
|url-status= live
}}</ref>

After the [[Congress of Vienna]] there was a degree of commercial cooperation between the various German states resulting in the German Customs Union (''[[Zollverein]]''). There were, however, still many barriers to trade until [[Bavaria]] took the lead in establishing the General German Commercial Code in 1856. As part of the code the ''Zollverein'' introduced the ''[[Zollpfund]]'' (Customs Pound) which was defined as exactly 500&nbsp;g and could be split into 30&nbsp;'lot'.<ref name="Zollmuseum">
{{cite book
|url = https://books.google.com/books?id=vnwuk-LpMGkC&q=zollpfund+30+lot+1854&pg=PA129
|title = Die Mass-und Gewichtsreformen in Deutschland im 19. Jahrhundert unter besonderer Berucksichtigung der Rolle Carl August Steinheils und der Bayerischen Akademie der Wissenschaften
|trans-title=The weights and measure reforms in Germany in the 19th century with special reference to Rolle Carl August and the Bavarian Academy of Sciences 
|last1 = Meyer-Stoll |first1 = Cornelia 
|page = 129
|isbn = 978-3-7696-0124-4
|publisher = Bayerischen Akademie der Wissenschaften [Bavarian Academy of Sciences]
|language = de
|location = Munich
|year = 2010
}}</ref> This unit was used for inter-state movement of goods, but was not applied in all states for internal use.

In 1832, [[Carl Friedrich Gauss]] studied the [[Earth's magnetic field]] and proposed adding the [[second]] to the basic units of the [[metre]] and the [[kilogram]] in the form of the [[Centimetre–gram–second system of units|CGS system]] ([[centimetre]], [[gram]], second). In 1836, he founded the ''Magnetischer Verein'', the first international scientific association, in collaboration with [[Alexander von Humboldt]] and [[Wilhelm Eduard Weber|Wilhelm Edouard Weber]]. [[Geophysics]] preceded physics{{citation needed|date=November 2023}} and contributed to the development of its methods. It was primarily a [[natural philosophy]] whose object was the study of natural phenomena such as the Earth's magnetic field, [[lightning]] and [[gravity]]. The coordination of the observation of geophysical phenomena in different points of the globe was of paramount importance and was at the origin of the creation of the first international scientific associations. The foundation of the ''Magnetischer Verein'' would be followed by that of the Central European Arc Measurement (German: [[International Association of Geodesy|''Mitteleuropäische Gradmessung'']]) on the initiative of [[Johann Jacob Baeyer]] in 1863, and by that of the [[World Meteorological Organization|International Meteorological Organisation]] whose second president, the Swiss [[meteorologist]] and [[physicist]], [[Heinrich von Wild]] represented [[Russian Empire|Russia]] at the [[General Conference on Weights and Measures|International Committee for Weights and Measures]] (CIPM).<ref>{{cite web|date=8 December 2015|title=History of IMO|url=https://public-old.wmo.int/en/about-us/who-we-are/history-IMO|archive-url=https://web.archive.org/web/20231218170901/https://public-old.wmo.int/en/about-us/who-we-are/history-IMO|url-status=dead|archive-date=18 December 2023|access-date=7 January 2021|website=World Meteorological Organization}}</ref><ref name=":4">{{cite web|title=Wild, Heinrich|url=https://hls-dhs-dss.ch/articles/028982/2014-11-11/|access-date=7 January 2021|website=hls-dhs-dss.ch|language=de}}</ref><ref>{{Cite web|last=|first=|date=1903|title=Heinrich Von Wild (1833-1902) in Comlté International Des Poids Et Mesures. Procès-Verbaux Des Séances. Deuxième Série. Tome Ii. Session De 1903.|url=https://www.bipm.org/utils/common/pdf/obituaries/1903_CIPM_CH&RU_WILD-Heinrich.pdf|url-status=dead|archive-url=https://web.archive.org/web/20210124084245/https://www.bipm.org/utils/common/pdf/obituaries/1903_CIPM_CH%26RU_WILD-Heinrich.pdf|archive-date=24 January 2021|access-date=|website=BIPM}}</ref> In 1867, the European Arc Measurement (German: ''[[International Association of Geodesy|Europäische Gradmessung]]'') called for the creation of a new, ''international prototype metre'' (IPM) and the arrangement of a system where national standards could be compared with it. The French government gave practical support to the creation of an International Metre Commission, which met in Paris in 1870 and again in 1872 with the participation of about thirty countries. The [[Metre Convention]] was signed on 20 May 1875 in Paris and the [[International Bureau of Weights and Measures]] was created under the supervision of the [[International Committee for Weights and Measures|CIPM]].

Although the Zollverein collapsed after the [[Austro-Prussian War]] of 1866, the metric system became the official system of measurement in the newly formed [[German Empire]] in 1872<ref name=Alder/>{{rp|350}} and of Austria in 1875.<ref name="PopularScience">
{{cite journal
|journal = Popular Science Monthly
|url = https://books.google.com/books?id=IyUDAAAAMBAJ&q=The+Metric+System+-+Shall+it+be+compulsory&pg=PA394
|title = The Metric System – Shall it be compulsory?
|author = W Leconte Stephens
|date = March 1904
|pages = 394–405
|access-date = 17 May 2011}}</ref> The Zollpfund ceased to be legal in Germany after 1877.<ref>{{cite web
|url = http://universal_lexikon.deacademic.com/3160/Pfund
|title = Pfund
|publisher = Universal-Lexikon
|access-date = 17 May 2011
|year = 2010
|language = de
|archive-date = 6 September 2014
|archive-url = https://web.archive.org/web/20140906091848/http://universal_lexikon.deacademic.com/3160/Pfund
|url-status = dead
}}</ref>

=== Italy (1797–1870) ===
[[File:Vicopisano-misure antiche.jpg |thumb|upright=1| Tablet showing conversions of legacy units of weights and measures to metric units, [[Vicopisano]], [[Tuscany]]. ]]

The [[Cisalpine Republic]], a North Italian republic set up by Napoleon in 1797 with its capital at [[Milan]], first adopted a modified form of the metric system based on the ''braccio cisalpino'' (Cisalpine cubit) which was defined to be half a metre.<ref name="metricItaly">
{{cite web
|url = http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Borgato.pdf
|title = The first applications of the metric system in Italy
|author = Maria Teresa Borgato
|work = The Global and the Local:The History of Science and the Cultural Integration of Europe. Proceedings of the 2nd ICESHS
|location = Cracow, Poland
|date = 6–9 September 2006
|publisher = The Press of the Polish Academy of Arts and Sciences
|access-date = 17 March 2011
|archive-date = 6 November 2020
|archive-url = https://web.archive.org/web/20201106070022/http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Borgato.pdf
|url-status = dead
}}</ref> In 1802 the Cisalpine Republic was renamed the [[Italian Republic (Napoleonic)|Italian Republic]], with Napoleon as its head of state. The following year the Cisalpine system of measure was replaced by the metric system.<ref name = metricItaly/>

In 1806, the Italian Republic was replaced by the [[Kingdom of Italy (Napoleonic)|Kingdom of Italy]] with Napoleon as its emperor. By 1812, all of Italy from Rome northwards was under the control of Napoleon, either as French Departments or as part of the Kingdom of Italy, ensuring that the metric system was in use throughout this region.

After the [[Congress of Vienna]], the various Italian states reverted to their original systems of measurements, but in 1845 the [[Kingdom of Sardinia (1720–1861)|Kingdom of Piedmont and Sardinia]] passed legislation to introduce the metric system within five years. By 1860, most of Italy had been unified under the King of Sardinia [[Victor Emmanuel II]]; and under ''Law 132 of 28 July 1861'' the metric system became the official system of measurement throughout the kingdom. Numerous ''Tavole di ragguaglio'' (conversion tables) were displayed in shops until 31 December 1870.<ref name = metricItaly/>

=== Netherlands (1799–1817) ===
The Netherlands (as the revolutionary [[Batavian Republic]]) began to use the metric system from 1799 but, as with its co-revolutionaries in France, encountered [[Mesures usuelles#Rationale behind the new system|numerous practical difficulties]]. Subsequently, as part of the [[First French Empire]] since 1809, the Netherlands used Napoleon's {{lang|FR|[[mesures usuelles]]}} from their introduction in 1812 until the fall of his Empire in 1815. Under the (Dutch) [[Weights and Measures Act]] of 21 August 1816 and the Royal decree of 27 March 1817 ({{lang|NL|Koningklijk besluit van den 27 Maart 1817}}), the newly formed [[Kingdom of the Netherlands]] abandoned the {{lang|FR|mesures usuelles}} in favour of the "Dutch" [[metric system]] ({{lang|NL|Nederlands metrisch stelsel}}) in which metric units were simply given the names of units of measure that were then in use: for instance the {{lang|NL|ons}} (ounce) was defined as 100&nbsp;g.<ref>
{{cite book
|url = https://archive.org/details/allereerstegron00ramagoog
|title = Allereerste Gronden der Cijferkunst
|author = Jacob de Gelder
|location = 's Gravenhage and Amsterdam
|language = nl
|year = 1824
|pages = [https://archive.org/details/allereerstegron00ramagoog/page/n364 155]–157
|publisher = de Gebroeders van Cleef
|trans-title=Introduction to Numeracy
|access-date = 2 March 2011
}}</ref>

=== Norway (1875) ===
In 1875, Norway was the first country to ratify the metre convention, and it was seen as an important step towards Norwegian independence. The decision to adopt the metric system is said to have been [[Norwegian Parliament's adoption of the metric system|the Norwegian Parliament's fastest decision]] in peacetime.

=== Portugal (1814) ===
In August 1814, Portugal officially adopted the metric system but with the names of the units substituted by [[Portuguese customary units|Portuguese traditional ones]]. In this system the basic units were the ''mão-travessa'' (hand) = 1&nbsp;[[decimetre]] (10&nbsp;''mão-travessas'' = 1&nbsp;''vara'' (yard) = 1&nbsp;metre), the ''[[canada (unit)|canada]]'' = 1&nbsp;litre and the ''libra'' (pound) = 1&nbsp;kilogram.<ref name="Fatima">{{cite web |author1=Fátima Paixão |author2=Fátima Regina Jorge |date=2006 |title=''Success and constraints in adoption of the metric system in Portugal'' |url=http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Paixao_Jorge.pdf |url-status=bot: unknown |archive-url=https://web.archive.org/web/20131203032144/http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Paixao_Jorge.pdf |archive-date=3 December 2013 |access-date=21 September 2022 |publisher=The Global and the Local: History of Science and the Cultural Integration of Europe}}</ref>

=== Spain (1700–1889) ===
[[File:General Carlos Ibáñez e Ibáñez de Ibero.jpg |thumb|right|upright=1| Don Carlos Ibáñez e Ibáñez de Ibero, first president of the [[International Association of Geodesy|International Geodetic Association]] and of the [[General Conference on Weights and Measures|International Committee for Weights and Measures]]. ]]

Until the ascent of the [[House of Bourbon|Bourbon]] monarchy in Spain in 1700, each region of Spain had its own system of measurement. The new Bourbon monarchy tried to centralise control and with it the system of measurement. There were debates regarding the desirability of retaining the [[Kingdom of Castile|Castilian]] units of measure or, in the interests of harmonisation, adopting the French system.<ref name="metricSpain">
{{cite web
|url = http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Navarro_Merino.pdf
|title = The units of length in the Spanish treatises of military engineering
|first1 = Juan Navarro
|last1 = Loidi
|first2 = Pilar Merino
|last2 = Saenz
|work = The Global and the Local: The History of Science and the Cultural Integration of Europe. Proceedings of the 2nd ICESHS
|location = Cracow, Poland
|date = 6–9 September 2006
|publisher = The Press of the Polish Academy of Arts and Sciences
|access-date = 17 March 2011
|archive-date = 3 October 2011
|archive-url = https://web.archive.org/web/20111003220229/http://www.2iceshs.cyfronet.pl/2ICESHS_Proceedings/Chapter_16/R-8_Navarro_Merino.pdf
|url-status = dead
}}</ref> Although Spain assisted [[Pierre Méchain|Méchain]] in his meridian survey, the Government feared the French revolutionary movement and reinforced the Castilian units of measure to counter such movements. By 1849 however, it proved difficult to maintain the old system and in that year the metric system became the legal system of measure in Spain.<ref name = metricSpain/>

The [[Spanish Royal Academy of Sciences|Spanish Royal Academy of Science]] urged the Government to approve the creation of a large-scale map of [[Spain]] in 1852. The following year [[Carlos Ibáñez e Ibáñez de Ibero]] was appointed to undertake this task. All the scientific and technical material had to be created. Ibáñez e Ibáñez de Ibero and Saavedra went to [[Paris]] to supervise the production by Brunner of a measuring instrument which they had devised and which they later compared with [[Jean-Charles de Borda|Borda]]'s double-toise N°1 which was the main reference for measuring all geodetic bases in France and whose length was by definition 3.8980732 metres at a specified temperature.<ref name=":2" /><ref>{{Cite book|last1=Delambre|first1=Jean-Baptiste (1749-1822) Auteur du texte|url=https://gallica.bnf.fr/ark:/12148/bpt6k1106055|title=Base du système métrique décimal, ou Mesure de l'arc du méridien compris entre les parallèles de Dunkerque et Barcelone. T. 3 /, exécutée en 1792 et années suivantes, par MM. Méchain et Delambre, rédigée par M. Delambre,...|last2=Méchain|first2=Pierre (1744-1804) Auteur du texte|date=1806–1810|publisher=|isbn=|location=|pages=139, 228|access-date=5 January 2021|archive-date=9 January 2021|archive-url=https://web.archive.org/web/20210109172924/https://gallica.bnf.fr/ark:/12148/bpt6k1106055|url-status=live}}</ref>

In 1865 the triangulation of [[Spain]] was connected with that of [[Portugal]] and [[France]]. In 1866 at the conference of the Association of Geodesy in [[Neuchâtel]], Ibáñez announced that [[Spain]] would collaborate in remeasuring the [[Paris meridian|French meridian arc]]. In 1879 Ibáñez and [[François Perrier (French Army officer)|François Perrier]] (representing France) completed the junction between the geodetic network of Spain and [[French Algeria|Algeria]] and thus completed the measurement of the [[Paris meridian|French meridian arc]] which extended from [[Shetland]] to the [[Sahara]].

In 1866, Spain and Portugal joined the Central European Arc Measurement which would become the [[International Association of Geodesy|European Arc Measurement]] the next year. In 1867 at the second general conference of the geodetic association held in Berlin, the question of an international standard unit of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth. The conference proposed according to recommendations drawn up by a committee chaired by [[Otto Wilhelm von Struve]] director of the [[Pulkovo Observatory]] in St. Petersburg the adoption of the [[metre]] and the creation of an international metre commission, after a preliminary discussion held in Neuchâtel between [[Johann Jacob Baeyer]] director of the Royal Prussian Geodetic Institute, [[Adolphe Hirsch]] founder of the [[Neuchâtel Observatory]] and [[Carlos Ibáñez e Ibáñez de Ibero]] Spanish representative, founder and first director of the [[Instituto Geográfico Nacional (Spain)|Instituto Geográfico Nacional]].<ref>{{cite book|last=|first=|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:108187:4/component/escidoc:272449/Generalbericht.mitteleurop%C3%A4ische.Gradmessung%201867.pdf|title=Bericht über die Verhandlungen der vom 30. September bis 7. October 1867 zu BERLIN abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung.|publisher=Central Bureau der Europäischer Gradmessung|year=1868|isbn=|location=Berlin|pages=14. 123–134}}</ref><ref>{{cite journal |last1=Débarbat |first1=Suzanne |author-link=Suzanne Débarbat |last2=Quinn |first2=Terry |date=January 2019 |title=Les origines du système métrique en France et la Convention du mètre de 1875, qui a ouvert la voie au Système international d'unités et à sa révision de 2018 |journal=Comptes Rendus Physique |volume=20 |issue=1–2 |pages=6–21 |bibcode=2019CRPhy..20....6D |doi=10.1016/j.crhy.2018.12.002 |doi-access=free}}</ref><ref>{{Cite web|last=Hirsch|first=Adolphe|date=1891|title=Don Carlos IBANEZ (1825-1891)|url=https://www.bipm.org/utils/common/pdf/obituaries/1891_CIPM_ES_IBANEZ-Don-Carlos.pdf|url-status=dead|archive-url=https://web.archive.org/web/20201026082704/https://www.bipm.org/utils/common/pdf/obituaries/1891_CIPM_ES_IBANEZ-Don-Carlos.pdf|archive-date=26 October 2020|access-date=|website=BIPM|pages=8–9}}</ref><ref>{{cite journal |last1=Drewes |first1=Hermann |last2=Kuglitsch |first2=Franz |last3=Adám |first3=József |last4=Rózsa |first4=Szabolcs |title=The Geodesist's Handbook 2016 |journal=Journal of Geodesy |date=October 2016 |volume=90 |issue=10 |pages=907–1205 |doi=10.1007/s00190-016-0948-z |bibcode=2016JGeod..90..907D |s2cid=125925505 |url=https://gfzpublic.gfz-potsdam.de/pubman/item/item_1981910_3/component/file_1985890/1981910.pdf}}</ref><ref>{{Cite web|last=Nacional|first=Instituto Geográfico|date=|title=Instituto Geográfico Nacional|url=https://www.ign.es/web/ign/portal/qsm-nuestra-historia|access-date=7 January 2021|website=Geoportal oficial del Instituto Geográfico Nacional de España|language=es-ES|archive-date=16 January 2021|archive-url=https://web.archive.org/web/20210116023805/https://www.ign.es/web/ign/portal/qsm-nuestra-historia|url-status=live}}</ref>
In November 1869 the French government issued invitations to join this commission. Spain accepted and [[Carlos Ibáñez e Ibáñez de Ibero]] took part in the Committee of preparatory research from the first meeting of the International Metre Commission in 1870. He became president of the permanent Committee of the International Metre Commission in 1872. In 1874 he was elected as president of the Permanent Commission of the [[International Association of Geodesy|European Arc Measurement]]. He also presided the General Conference of the [[International Association of Geodesy|European Arc Measurement]] held in Paris in 1875, when the association decided the creation of an international geodetic standard for the bases' measurement.<ref>{{Cite book|url=http://gallica.bnf.fr/ark:/12148/bpt6k949666|title=Histoire abrégée de l'astronomie / par Ernest Lebon,...|last=Lebon|first=Ernest (1846–1922) Auteur du texte|date=1899|publisher=Gauthier-Villars|location=Paris|pages=171|access-date=12 January 2018|archive-date=24 August 2017|archive-url=https://web.archive.org/web/20170824140556/http://gallica.bnf.fr/ark:/12148/bpt6k949666|url-status=live}}</ref> He represented Spain at the 1875 conference of the [[Metre Convention]], which was ratified the same year in Paris. The Spanish geodesist was elected as the first president of the [[International Committee for Weights and Measures]]. His activities resulted in the distribution of a platinum and iridium prototype of the [[metre]] to all States parties to the [[Metre Convention]] during the first meeting of the [[General Conference on Weights and Measures]] in 1889. These prototypes defined the metre right up until 1960.[[File:Bulletin de la Soci neuchloise des sciences naturelles (1898-) (20409300876).jpg|thumb|upright=0.75|Adolphe Hirsch, secretary of the [[International Association of Geodesy|International Geodetic Association]] and of the [[General Conference on Weights and Measures|International Committee for Weights and Measures]]]]

=== Switzerland (1801–1877) ===
[[File:Guillaume-Henri Dufour.jpg|left|thumb|upright=0.75|Guillaume Henri Dufour, founder of [[Swisstopo]]. ]]
[[File:Heinrich Wild.jpg |thumb|left|upright=0.75| Heinrich von Wild, president of the [[International Meteorological Organization]] and member of the [[General Conference on Weights and Measures|International Committee for Weights and Measures]]. ]]

In 1801, the [[Helvetic Republic]] at the instigation of [[Johann Georg Tralles]] promulgated a law introducing the metric system. However this was never applied, because in 1803 the competence for weights and measures returned to the [[Cantons of Switzerland|cantons]]. On the territory of the current [[canton of Jura]], then annexed to France ([[Mont-Terrible]]), the metre was adopted in 1800. The [[Canton of Geneva]] adopted the metric system in 1813, the [[canton of Vaud]] in 1822, the [[canton of Valais]] in 1824 and the [[canton of Neuchâtel]] in 1857. In 1835, twelve cantons of the [[Swiss Plateau]] and the north-east adopted a concordat based on the federal foot (exactly 0.3 m) which entered into force in 1836. The cantons of [[Central Switzerland|central]] and [[eastern Switzerland]], as well as the Alpine cantons, continued to use the old measures.<ref name=":5">{{cite web|title=Système métrique|url=https://hls-dhs-dss.ch/articles/013754/2014-05-22/|access-date=8 January 2021|website=hls-dhs-dss.ch|language=fr|archive-date=10 January 2021|archive-url=https://web.archive.org/web/20210110034838/https://hls-dhs-dss.ch/articles/013754/2014-05-22/|url-status=live}}</ref><ref>{{Cite web|title=Journal de Genève - 22.03.1854 - Page 1|url=https://www.letempsarchives.ch/page/JDG_1854_03_22/1/article/5203313|access-date=24 February 2021|website=www.letempsarchives.ch|archive-date=7 November 2023|archive-url=https://web.archive.org/web/20231107040659/https://www.letempsarchives.ch/page/JDG_1854_03_22/1/article/5203313|url-status=live}}</ref>

[[Guillaume Henri Dufour|Guillaume-Henri Dufour]] founded in 1838 in [[Geneva]] a topographic office (the future [[Swisstopo|Federal Office of topography]]), which published under his direction, from 1845 to 1864, the first official [[Topographic Map of Switzerland|map of Switzerland]], on the basis of new cantonal measurements. This map at [[Scale (map)|1:100,000]] engraved on copper, suggested the relief by hatching and shadows. The map projection adopted by the commission was the [[Bonne projection]], centred on the [[Bern]] Observatory (5° 6<nowiki>' 10.8''</nowiki> east of [[Paris meridian]]), although this point was much closer to the western end of Switzerland than to its eastern end. But its position was well known, and there was no more central [[observatory]]. The scale was set at 1:100 000 because it was considered more suitable for a country as rugged as Switzerland than the 1:80 000 adopted for the large [[Geography of France|map of France]] and the two maps were in any case inconsistent, as the meridians of the [[Cartography of Switzerland|map of Switzerland]] tilted in the opposite direction to those of the map of France. The map commission wanted to adopt decimal measures; and Switzerland did not have an already existing map which, like the [[Cassini map]], used a scale close to 1:86 400, i.e. 1 [[line (unit)|line]] ({{frac|1|12}} of a French inch) to 100 [[toise]]s (i.e. 600 French feet). The [[metre]] was adopted as a linear measure, and the entire map was divided into twenty-five sheets: five east–west and five north–south. Each sheet of the map showed two scales, one purely [[Metric system|metric]], the other in Swiss [[League (unit)|leagues]] 4,800 metres in length. The frame was divided into [[Degree (angle)|sexagesimal]] [[Minute and second of arc|minutes]] and centesimal minutes; the latter, each subdivided into ten parts, had the advantage of showing [[Kilometre]]s in the direction of the [[Meridian (geography)|meridians]]; so that there were new scales on the sides of the sheet to evaluate the distances.<ref name=":6">{{Cite web|title=Cartographie|url=https://hls-dhs-dss.ch/articles/008258/2014-11-26/|access-date=12 March 2021|website=hls-dhs-dss.ch|language=fr|archive-date=2 February 2021|archive-url=https://web.archive.org/web/20210202081004/https://hls-dhs-dss.ch/articles/008258/2014-11-26/|url-status=live}}</ref><ref name=":7">{{cite journal |last1=Dufour |first1=G.-H. |title=Notice sur la carte de la Suisse dressée par l'État Major Fédéral |journal=Le Globe. Revue genevoise de géographie |date=1861 |volume=2 |issue=1 |pages=5–22 |doi=10.3406/globe.1861.7582}}</ref><ref>{{Cite web|title=Systèmes de référence historiques|url=https://www.swisstopo.admin.ch/fr/connaissances-faits/histoire-collections/cartes-historiques/references-historiques.html|access-date=12 March 2021|website=Office fédéral de topographie swisstopo|language=fr|archive-date=26 November 2020|archive-url=https://web.archive.org/web/20201126212909/https://www.swisstopo.admin.ch/fr/connaissances-faits/histoire-collections/cartes-historiques/references-historiques.html|url-status=dead}}</ref>

According to the [[Swiss Federal Constitution|1848 Constitution]] the federal foot was to come into force throughout the country. In [[Geneva]], a committee chaired by [[Guillaume Henri Dufour]] militated in favor of maintaining the decimal metric system in the French-speaking cantons and against the standardization of weights and measures in Switzerland on the basis of the metric foot. In 1868 the metric system was legalized alongside the federal foot, which was a first step towards its definitive introduction. Cantonal calibrators were supervised by a [[Federal Institute of Metrology|Federal Bureau of Verification]] created in 1862, whose management was entrusted to [[Heinrich von Wild]] from 1864. In 1875, the responsibility for weights and measures was transferred back from the cantons to the Confederation, and [[Switzerland]] (represented by [[Adolphe Hirsch]]) joined the [[Metre Convention]]. The same year a federal law imposed the metric system from 1 January 1877. In 1977, Switzerland joined the [[International System of Units]].<ref name=":5" /><ref name=":4" /><ref>{{Cite web|title=Hirsch, Adolphe|url=https://hls-dhs-dss.ch/articles/032026/2005-05-10/|access-date=8 January 2021|website=hls-dhs-dss.ch|language=fr|archive-date=24 November 2020|archive-url=https://web.archive.org/web/20201124232607/https://hls-dhs-dss.ch/articles/032026/2005-05-10/|url-status=live}}</ref><ref>{{Cite web|title=Journal de Genève - 22.03.1854 - Page 1|url=https://www.letempsarchives.ch/page/JDG_1854_03_22/1/article/5203313|access-date=12 March 2021|website=www.letempsarchives.ch|archive-date=7 November 2023|archive-url=https://web.archive.org/web/20231107040659/https://www.letempsarchives.ch/page/JDG_1854_03_22/1/article/5203313|url-status=live}}</ref><ref>{{Cite web|title=Journal de Genève - 14.02.1852 - Page 4|url=https://www.letempsarchives.ch/page/JDG_1852_02_14/4|access-date=12 March 2021|website=www.letempsarchives.ch|archive-date=7 November 2023|archive-url=https://web.archive.org/web/20231107040705/https://www.letempsarchives.ch/page/JDG_1852_02_14/4|url-status=live}}</ref>

=== United Kingdom (1824–present) ===
{{Main|Metrication in the United Kingdom}}

The [[Weights and Measures Act 1824]] ([[5 Geo. 4]]. c. 74) imposed one standard 'imperial' system of weights and measures on the British Empire.<ref>
{{cite web
|url = http://www.parliament.uk/about/living-heritage/transformingsociety/tradeindustry/industrycommunity/keydates/
|title = Industry and community – Key dates
|publisher = United Kingdom Parliament
|access-date = 28 March 2011
|archive-date = 6 November 2010
|archive-url = https://web.archive.org/web/20101106184932/http://www.parliament.uk/about/living-heritage/transformingsociety/tradeindustry/industrycommunity/keydates/
|url-status = live
}}</ref> The effect of this act was to standardise existing British units of measure rather than to align them with the metric system.

During the next eighty years a number of parliamentary select committees recommended the adoption of the metric system, each with a greater degree of urgency, but Parliament prevaricated. A select committee report of 1862 recommended compulsory metrication, but with an "Intermediate permissive phase"; Parliament responded in 1864 by legalising metric units only for 'contracts and dealings'.<ref name="Hyttel">
{{cite thesis
 |degree      = BA
 |title       = Working man's pint – An investigation of the implementation of the metric system in Britain 1851–1979
 |url         = http://ukma.org.uk/sites/default/files/hyttel_metrication.pdf
 |author      = Frederik Hyttel
 |date        = May 2009
 |publisher   = Bath Spa University
 |location    = [[Bath, Somerset|Bath]], United Kingdom
 |access-date  = 29 March 2011
 |archive-url  = https://web.archive.org/web/20160306063341/http://ukma.org.uk/sites/default/files/hyttel_metrication.pdf
 |archive-date = 6 March 2016
 |url-status     = dead
 |df          = dmy-all
}}</ref> The United Kingdom initially declined to sign the [[Treaty of the Metre]], but did so in 1883. Meanwhile, British scientists and technologists were at the forefront of the metrication movement – it was the [[British Association for the Advancement of Science]] that promoted the [[CGS system of units]] as a coherent system<ref name="SIBrochure">{{SIBrochure8th}}</ref>{{rp| 109}} and it was the British firm [[Johnson Matthey]] that was accepted by the CGPM in 1889 to cast the international prototype metre and kilogram.<ref name="CGPMprototypes">{{cite journal |last1=Jabbour |first1=Z.J. |last2=Yaniv |first2=S.L. |title=The kilogram and measurements of mass and force |journal=Journal of Research of the National Institute of Standards and Technology |date=January 2001 |volume=106 |issue=1 |pages=25–46 |doi=10.6028/jres.106.003 |pmid=27500016 |pmc=4865288}}</ref>

In 1895, another parliamentary select committee recommended the compulsory adoption of the metric system after a two-year permissive period. The [[Weights and Measures (Metric System) Act 1897]] ([[60 & 61 Vict.]] c. 46) legalised the metric units for trade, but did not make them mandatory.<ref name = Hyttel/> A bill to make the metric system compulsory to help the British industrial base fight off the challenge of the nascent German base passed through the House of Lords in 1904, but did not pass in the House of Commons before the next general election was called. Following opposition by the Lancashire cotton industry, a similar bill was defeated in the House of Commons in 1907 by 150 votes to 118.<ref name = Hyttel/>

In 1965, the UK began an official programme of metrication, and as of {{currentyear}}, in the [[United Kingdom]] the metric is the official measurement system for all regulated trading by weight or measure purposes, however the imperial [[pint]] remains the sole legal unit for milk in returnable bottles and for draught beer and cider in British pubs. Imperial units are also legally permitted to be used alongside metric units on food packaging and price indications for goods sold loose.<ref>{{cite web |title=Weights and measures: the law |url=https://www.gov.uk/weights-measures-and-packaging-the-law |access-date=2024-02-12 |website=GOV.UK |language=en |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030170848/https://www.gov.uk/weights-measures-and-packaging-the-law |url-status=live }}</ref> The UK government undertook a "Choice on units of measurement: consultation response", and found just over 1% of respondents wish to revert to an increase the use of imperial units,  and as such kept the current regulations on the sale of goods.<ref>{{cite web |title=Choice on units of measurement: consultation response |url=https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales/outcome/choice-on-units-of-measurement-consultation-response |access-date=2024-02-12 |website=GOV.UK |language=en |archive-date=20 January 2024 |archive-url=https://web.archive.org/web/20240120162306/https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales/outcome/choice-on-units-of-measurement-consultation-response |url-status=live }}</ref>

In addition imperial units may be used exclusively where a product is sold by description, rather than by weight/mass/volume: e.g. television screen and clothing sizes tend to be given in inches only, but a piece of material priced per inch would be unlawful unless the metric price was also shown.

The general public still use imperial units in common language for their height and weight, and imperial units are the norm when discussing longer distances such as journeys by car, but otherwise metric measurements are often used.{{citation needed|date=August 2022}}

=== United States (1830–present) ===
{{Main|Metrication in the United States}}
[[File:Ferdinand Randolph Hassler LCCN2003655032.jpg|thumb|upright=0.75|Ferdinand Rudolph Hassler, first superintendent of the [[United States Coast and Geodetic Survey|United States Coast Survey]]|left]]
In 1805 a Swiss geodesist [[Ferdinand Rudolph Hassler]] brought copies of the French metre and kilogram to the United States.<ref>{{Cite web |url=http://www.f-r-hassler.ch/en/emigration/index.html |title=Emigration: Off to New Shores |website=E-Expo Ferdinand Rudolf Hassler |publisher=METAS |access-date=19 December 2017 |archive-date=12 February 2018 |archive-url=https://web.archive.org/web/20180212000054/http://www.f-r-hassler.ch/en/emigration/index.html |url-status=live }}</ref><ref name=":1">{{Cite journal|last=Cajori|first=Florian|date=1921|title=Swiss Geodesy and the United States Coast Survey|url=https://www.jstor.org/stable/6721|journal=The Scientific Monthly|volume=13|issue=2|pages=117–129|bibcode=1921SciMo..13..117C|issn=0096-3771|access-date=4 January 2021|archive-date=6 June 2021|archive-url=https://web.archive.org/web/20210606111103/https://www.jstor.org/stable/6721|url-status=live}}</ref> In 1830 the Congress decided to create uniform standards for length and weight in the United States.<ref name=":0">{{Cite web |url=http://www.f-r-hassler.ch/en/weights/index.html |title=Weights and Measures: New Standards for the USA |website=E-Expo Ferdinand Rudolf Hassler |publisher=METAS |access-date=19 December 2017 |archive-date=12 February 2018 |archive-url=https://web.archive.org/web/20180212000139/http://www.f-r-hassler.ch/en/weights/index.html |url-status=live }}</ref> [[Ferdinand Rudolph Hassler|Hassler]] was mandated to work out the new standards and proposed to adopt the [[metric system]].<ref name=":0" /> The Congress opted for the British Parliamentary Standard from 1758 and the Troy Pound of Great Britain from 1824 as length and weight standards.<ref name=":0" /> Nevertheless, the primary baseline of the Survey of the Coast (renamed the United States Coast Survey in 1836 and the [[United States Coast and Geodetic Survey]] in 1878) was measured in 1834 at [[Fire Island]] using four {{convert|2|m|adj=on}} iron bars constructed after Hassler's specification in the United Kingdom and brought back in the United States in 1815.<ref>{{Cite web |url=https://www.nist.gov/sites/default/files/documents/nvl/HasslerSP1068.pdf |title=NIST Special Publication 1068 Ferdinand Rudolph Hassler (1770–1843) A Twenty Year Retrospective, 1987–2007 |website=NIST |pages=51–52 |access-date=27 November 2017 |archive-date=31 January 2017 |archive-url=https://web.archive.org/web/20170131034513/https://www.nist.gov/sites/default/files/documents/nvl/HasslerSP1068.pdf |url-status=dead}}</ref><ref>{{Cite web |url=http://www.f-r-hassler.ch/en/interlude/index.html |title=Interlude in Europe: Ups... and Downs... |website=E-Expo Ferdinand Rudolf Hassler |publisher=METAS |access-date=19 December 2017 |archive-date=12 February 2018 |archive-url=https://web.archive.org/web/20180212000220/http://www.f-r-hassler.ch/en/interlude/index.html |url-status=live }}</ref><ref name=":1" /> All distances measured by the Survey of the Coast, Coast Survey, and Coast and Geodetic Survey were referred to the metre.<ref name=":2">{{cite journal |title=XIII. Results of the comparisons of the standards of length of England, Austria, Spain, United States, Cape of Good Hope, and of a second Russian standard, made at the Ordnance Survey Office, Southampton. With a preface and notes on the Greek and Egyptian measures of length by Sir Henry James |journal=Philosophical Transactions of the Royal Society of London |date=31 December 1873 |volume=163 |pages=445–469 |doi=10.1098/rstl.1873.0014 |doi-access=free}}</ref><ref name=":3">{{Cite book|last=Hassler|first=Ferdinand Rudolf|date=1825|title=Transactions of the American Philosophical Society|url=https://www.biodiversitylibrary.org/page/4482470|access-date=|volume=2|page=252|archive-date=8 April 2023|archive-url=https://web.archive.org/web/20230408175517/https://www.biodiversitylibrary.org/page/4482470|url-status=live}}</ref> In 1866 the [[United States Congress]] passed a bill making it lawful to use the metric system in the United States. The bill, which was permissive rather than mandatory in nature, defined the metric system in terms of [[United States customary units|customary units]] rather than with reference to the international prototype metre and kilogram.<ref>
{{cite web
 |url=http://lamar.colostate.edu/~hillger/laws/metric-act-bill.html 
 |title=H.R. 596, An Act to authorize the use of the metric system of weights and measures 
 |author=29th Congress of the United States, Session 1 
 |date=13 May 1866 |access-date=19 May 2011 |url-status=dead 
 |archive-url=https://web.archive.org/web/20150705015307/https://lamar.colostate.edu/~hillger/laws/metric-act-bill.html 
 |archive-date=5 July 2015
}}</ref><ref name=Barbrowetal/>{{rp|10–13}} Ferdinand Rudolph Hassler's use of the metre in coastal surveying, which had been an argument for the introduction of the [[Metric Act of 1866]] allowing the use of the metre in the United States, probably also played a role in the choice of the metre as international scientific unit of length and the proposal by the [[International Association of Geodesy|European Arc Measurement]] (German: ''Europäische Gradmessung'') to “establish a European [[International Bureau of Weights and Measures|international bureau for weights and measures]]”.<ref name=":3" /><ref name=":2" /><ref>{{Cite web|title=Metric Act of 1866 – US Metric Association|url=https://usma.org/laws-and-bills/metric-act-of-1866#locale-notification|access-date=4 January 2021|website=usma.org|archive-date=28 February 2021|archive-url=https://web.archive.org/web/20210228052918/https://usma.org/laws-and-bills/metric-act-of-1866#locale-notification|url-status=live}}</ref><ref>{{Cite book|last=|first=|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:108187:4/component/escidoc:272449/Generalbericht.mitteleurop%C3%A4ische.Gradmessung%201867.pdf|title=Bericht über die Verhandlungen der vom 30. September bis 7. October 1867 zu BERLIN abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung|publisher=Central-Bureau der Europäischen Gradmessung|year=1868|isbn=|location=Berlin|pages=123–134|language=de}}</ref>

By 1893, the reference standards for customary units had become unreliable. Moreover, the United States, being a signatory of the [[Metre Convention]] was in possession of national prototype metres and kilograms that were calibrated against those in use elsewhere in the world. This led to the [[Mendenhall Order]] which redefined the customary units by referring to the national metric prototypes, but used the conversion factors of the 1866 act.<ref name="Barbrowetal">
{{cite book
 |title       = Weights and Measures Standards of the United States: A brief history
 |last1       = Barbrow |first1      = Louis E.
 |last2       = Judson |first2      = Lewis V.
 |publisher   = NIST
 |year        = 1976
 |url         = https://www.nist.gov/pml/pubs/sp447/index.cfm |access-date  = 19 May 2011 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110603064530/https://www.nist.gov/pml/pubs/sp447/index.cfm
 |archive-date = 3 June 2011
}}</ref>{{rp|16–20}} In 1896, a bill that would make the metric system mandatory in the United States was presented to Congress. Twenty-three of the 29 people who gave evidence before the congressional committee who were considering the bill were in favor of it, but six were against. Four of these six dissenters represented manufacturing interests and the other two were from the United States Revenue service. The grounds cited were the cost and inconvenience of the change-over. The bill was not enacted. Subsequent bills suffered a similar fate.<ref name="PopularScience" />

The United States mandated the acceptance of the metric system in 1866 for commercial and legal proceedings, without displacing their customary units.<ref name="United States Metric Laws and Treaties">{{cite web |url=http://ts.nist.gov/WeightsAndMeasures/Metric/upload/HR-596-Metric-Law-1866.pdf |title=Metric Act of 1866 |publisher=Metric Program, Weights and Measures Division, United States National Institute of Standards, Technology and Technology |access-date=10 November 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100527161529/http://ts.nist.gov/WeightsAndMeasures/Metric/upload/HR-596-Metric-Law-1866.pdf |archive-date=27 May 2010}}<br /> {{cite web | title = U.S. Metric System (SI) Legal Resources | url = http://ts.nist.gov/WeightsAndMeasures/Metric/Federal_Metric_Policy.cfm#legal | publisher = Metric Program, Weights and Measures Division, United States National Institute of Standards, Technology and Technology | access-date = 11 November 2009 | url-status = dead | archive-url = https://web.archive.org/web/20090801172441/http://ts.nist.gov/WeightsAndMeasures/Metric/Federal_Metric_Policy.cfm#legal | archive-date = 1 August 2009 | df = dmy-all}}</ref> The non-mandatory nature of the adoption of the SI has resulted in a much slower pace of adoption in the US than in other countries.<ref>{{cite journal |last1=Smith |first1=Jeanette C. |title=Take Me to Your Liter |journal=Journal of Government Information |date=September 1998 |volume=25 |issue=5 |pages=419–438 |doi=10.1016/S1352-0237(98)00030-6}}</ref>

In 1971, the US [[National Institute of Standards and Technology|National Bureau of Standards]] completed a three-year study of the impact of increasing worldwide metric use on the US. The study concluded with a report to Congress entitled ''[[A Metric America&nbsp;– A Decision Whose Time Has Come]]''. Since then metric use has increased in the US, principally in the manufacturing and educational sectors. Public Law 93-380, enacted 21 August 1974, states that it is the policy of the US to encourage educational agencies and institutions to prepare students to use the metric system of measurement with ease and facility as a part of the regular education program. On 23 December 1975, President Gerald Ford signed Public Law 94–168, the [[Metric Conversion Act]] of 1975. This act declares a national policy of coordinating the increasing use of the metric system in the US. It established a US Metric Board whose functions as of 1 October 1982 were transferred to the Dept of Commerce, Office of Metric Programs, to coordinate the voluntary conversion to the metric system.<ref>
{{cite book
 |editor = Howard B. Bradley
 |title = Petroleum Engineering Handbook
 |pages = 1–69
 |year = 1987
 |publisher = Society of Petroleum Engineers
 |isbn = 978-1555630102
}}</ref>

In January 2007 [[NASA]] decided to use metric units for all future Moon missions, in line with the practice of other space agencies.<ref name="MetricMoon">{{cite web
 |url=https://science.nasa.gov/science-news/science-at-nasa/2007/08jan_metricmoon/
 |title=Metric Moon
 |year=2007
 |publisher=[[NASA]]
 |access-date=6 April 2010
 |archive-date=11 July 2010
 |archive-url=https://web.archive.org/web/20100711000119/http://science.nasa.gov/science-news/science-at-nasa/2007/08jan_metricmoon/
 |url-status=dead
}}</ref>

=== Other English-speaking countries ===

The British metrication programme signalled the start of metrication programmes elsewhere in the [[Commonwealth of Nations|Commonwealth]], though India had started its programme in 1959, six years before the United Kingdom. South Africa (then not a member of the Commonwealth) set up a Metrication Advisory Board in 1967, New Zealand set up its Metric Advisory Board in 1969, Australia passed the Metric Conversion Act in 1970 and Canada appointed a Metrication Commission in 1971. 
[[File:Canadian canned food labels showing imperial and metric units of measurement.jpg|thumb|upright=1.35|left|The metric units of measurement on Canadian canned food labels are merely the equivalent of the still widely used imperial units such as the ounce.]]
Metrication in Australia, New Zealand and South Africa was essentially complete within a decade, while in Canada metrication has been halted since the 1970s. In Canada, the [[square foot]] is still widespread for commercial and residential advertisements and partially in construction because of the close trade relations with the United States. Metric measurements on food products such as canned food are often merely the equivalent of the still widely used imperial units of measurement such as the ounce and the pound. Butter in Canada is sold in 454 g packagings, which is the equivalent of one pound. The [[Rail transport in Canada|railways of Canada]] such as the [[Canadian National Railway|Canadian National]] and [[Canadian Pacific Railway|Canadian Pacific]] as well as [[commuter rail]] services continue to measure their trackage in miles and speed limits in miles per hour because they also operate in the United States (although urban railways including [[Rapid transit|subways]] and [[light rail]] have adopted kilometres and kilometres per hour).<ref>{{cite web |url=http://www.tc.gc.ca/eng/railsafety/rules-tce31-98.htm |title=A. Classes of Track - Transport Canada |website=www.tc.gc.ca |access-date=11 January 2022 |archive-url=https://web.archive.org/web/20120825070252/http://www.tc.gc.ca/eng/railsafety/rules-tce31-98.htm |archive-date=25 August 2012 |url-status=dead}}</ref> Canadian railcars show weight figures in both imperial and metric. Most other Commonwealth countries adopted the metric system during the 1970s.<ref>
{{cite web
 |url=http://lamar.colostate.edu/~hillger/internat.htm 
 |title=Metrication status and history 
 |publisher=United States Metrication Association 
 |year=2009 
 |access-date=19 May 2011 |url-status=dead 
 |archive-url=https://web.archive.org/web/20100724200113/http://lamar.colostate.edu/~hillger/internat.htm 
 |archive-date=24 July 2010
}}</ref>

Apart from the United Kingdom and Canada, which have effectively halted their metrication programs, the great majority of countries using the imperial system have completed official metrication during the second half of the 20th century or the first decade of the 21st century. The most recent to complete this process was the [[Republic of Ireland]], which began metric conversion in the 1970s and completed it in early 2005.<ref>{{cite web|url=https://www.independent.co.uk/life-style/motoring/features/ireland-goes-metric--fast-531570.html|archive-url=https://web.archive.org/web/20141029022100/http://www.independent.co.uk/life-style/motoring/features/ireland-goes-metric--fast-531570.html|url-status=dead|archive-date=29 October 2014|title=Ireland goes metric - fast|work=The Independent|access-date=24 November 2014}}</ref> [[Hong Kong units of measurement|Hong Kong uses three systems]] (Chinese, imperial, and metric) and all three are permitted for use in trade.<ref name="Ordinance">{{Cite web |url=http://www.hklii.hk/eng/hk/legis/ord/68/sch2.html |title=Cap 68 Sched 2 Units of Measurement and Permitted Symbols or Abbreviations of Units of Measurement Lawful for Use for Trade |access-date=28 April 2020 |archive-date=3 September 2015 |archive-url=https://web.archive.org/web/20150903233217/http://www.hklii.hk/eng/hk/legis/ord/68/sch2.html |url-status=dead}}</ref>

== Global status of metrication ==
=== Status by country/region ===

[[File:Metric_and_imperial_systems_(2019).svg|upright=3.4|thumb|center|Countries by their dominant system of measurement ([[Metric system|metric]], [[Imperial units|imperial]], and [[US customary]]) as of 2025 (based on popular and official usage)]]

''Links in the '''country/region''' point to articles about metrication in that country/region.''<ref>
{{cite web
 |url          = http://www.cl.cam.ac.uk/~mgk25/volatile/dunn-papersizes.pdf
 |title        = Notes on the standardization of paper sizes
 |author       = AD Dunn
 |location     = Ottawa
 |page         = 11
 |year         = 1969
 |access-date  = 7 December 2018
 |archive-date = 15 November 2017
 |archive-url  = https://web.archive.org/web/20171115213957/http://www.cl.cam.ac.uk/~mgk25/volatile/dunn-papersizes.pdf
 |url-status   = live
}}</ref>

<!-- NOTE: the "<span style="display:none">SOMETHING</span>" markups ensure correct sorting order. -->
{| class="wikitable sortable plainrowheaders"
|+Overview of global metrication
|-
!scope="col"| Year official metrication<br /> process started<ref>{{cite book
 | title          = The International Bureau of Weights and Measures 1875–1975: NBS Special Publication 420
 | url            = https://archive.org/details/internationalbur420page
 | quote          = gram-atom .
 | page           = [https://archive.org/details/internationalbur420page/page/244 244]
 | date           = 20 May 1975
| editor1-last   = Page
 | editor1-first  = Chester H
 | editor2-last   = Vigoureux
 | editor2-first  = Paul
 | publisher      = National Bureau of Standards
 | location       = [[Washington, D.C.]]
}}</ref><ref>{{cite book
 |url = https://books.google.com/books?id=uYCNFkRgXCoC&q=Revolution+in+Measurement%3A+Western+European+Weights+and+Measures+Since+the+Age+of+Science
 | title          = Revolution in Measurement – Western European Weights and Measures Since the Age of Science
 | first1         = Ronald Edward
 | last1          = Zupko
 | series         = Memoirs of the American Philosophical Society
 | volume         = 186
 | year           = 1990
 | pages          = 242–245
 | isbn           = 978-0-87169-186-6
 |access-date      = 21 April 2012
}}</ref><ref>{{cite book
|url = https://archive.org/stream/metricversuseng00boargoog#page/n4/mode/2up
|title=The Metric ''versus'' the English System of Weights and Measures
|id = Research Report Number 42
|date = October 1921
|pages = 12–13
|publisher = National Industrial Conference Board
|access-date = 1 June 2013}}</ref>
!scope="col"| Country/Region
!scope="col" width=180|Previous system<br />of measure
!scope="col" class=unsortable|Current official status of metrication
|-
| 1795
!scope="row"| France
| [[French units of measurement|French]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1814
!scope="row"| Portugal<ref group="Note">Including [[Portuguese Empire|Portuguese colonies]], most of them now independent countries.</ref>
| [[Portuguese customary units|Portuguese]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1820
!scope="row"| Belgium
| [[Belgian units of measurement|Belgian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Netherlands
| [[Dutch units of measurement|Dutch]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1843
!scope="row"| Algeria
| [[Algerian units of measurement|Algerian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1848
!scope="row"| [[Metrication in Chile|Chile]]
| [[Chilean units of measurement|Chilean (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1852<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/international.html |archive-url=https://web.archive.org/web/20120831004546/http://lamar.colostate.edu/~hillger/international.html |url-status=dead |archive-date=31 August 2012 |title=Metrication in Mexico |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014}}</ref>
!scope="row"| Mexico
| [[Mexican units of measurement|Mexican (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, (some national and regional units are still in use and some [[United States customary units]] also in use in some industries)
|-
!scope="row"| Spain
| [[Spanish customary units|Spanish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1860<ref>{{Cite book|last=Washburn|first=Edward Wight|url=https://books.google.com/books?id=zkErAAAAYAAJ&q=international+critical+tables+1926&pg=PA10|title=International Critical Tables of Numerical Data, Physics, Chemistry and Technology|date=1926|publisher=National Research Council}}</ref>{{br}}1906<ref>{{Cite web|title=Act No. 1519, s. 1906 {{!}} GOVPH|url=https://www.officialgazette.gov.ph/1906/08/03/act-no-1519-s-1906/|access-date=27 February 2021|website=Official Gazette of the Republic of the Philippines}}{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes}}</ref>
!scope="row"| Philippines
| [[Philippine units of measurement|Philippine]] ([[Spanish customary units|Spanish]], [[United States customary units|US customary]] and local)
| bgcolor="#CEE6F2" data-sort-value="1blue" | Mainly metric. The Philippines first adopted the metric system in 1860 because of the Spanish Colonial government; US customary units were introduced by the American Colonial government; however, the metric system was made the official system of measurement in 1906 through Act No. 1519, s. 1906. US customary units still in use for body measurements and small products while the metric system is used for larger measurements; e.g. floor area, highway length, tonnage.
|-
| 1861
!scope="row"| Italy
| [[Italian units of measurement|Italian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1862<ref>{{cite web|url=http://www.inmetro.gov.br/inmetro/historico.asp|title=Histórico do Inmetro|publisher=Inmetro.gov.br|access-date=24 November 2014|archive-date=28 February 2015|archive-url=https://web.archive.org/web/20150228101309/http://www.inmetro.gov.br/inmetro/historico.asp|url-status=dead}}</ref>
!scope="row"| Brazil
| [[Brazilian units of measurement|Brazilian (variants of Portuguese)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, but some non-metric units are used for specific areas: rural land – [[alqueire]]; cattle weight – [[arroba]]; screen sizes – polegada (inch); tyre pressure – libra-força por polegada quadrada, but referred by its English abbreviation: psi.
|-
!scope="row"| [[Metrication in Peru|Peru]]
| [[Peruvian units of measurement|Peruvian (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, but inches (''pulgadas'') are used for screen sizes and tires. Fuel is sold in US gallons (''galones'').
|-
|rowspan="2"| 1863
!scope="row"| Uruguay
| [[Uruguayan units of measurement|Uruguayan (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Argentina
| [[Argentine units of measurement|Argentine (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1864
!scope="row"| Romania
| [[Romanian units of measurement|Romanian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1868
!scope="row" data-sort-value="Germany" | [[North German Confederation]]
| [[German units of measurement|German]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1869
!scope="row" data-sort-value="Germany" |[[Southern Germany|South German states]]
| [[German units of measurement|German]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1871
!scope="row"| Austria
| [[Obsolete Austrian units of measurement|Austrian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1872<ref group="Note">Many German states, particularly those under French tutelage during the Napoleonic Wars ([[Rheinbund]]) adopted the metre 1806–15.</ref>
!scope="row"| Germany
| [[German units of measurement|German]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1873<ref>{{cite web
|url = http://www.dmdm.rs/en/Istorijat.php
|title = History
|publisher = Ministry of finance and economy: Directorate of Measures and Precious Metals
|access-date = 28 March 2013
|location = [[Belgrade|Beograd]], [[Serbia]]
|archive-date = 5 March 2016
|archive-url = https://web.archive.org/web/20160305045135/http://www.dmdm.rs/en/Istorijat.php
|url-status = dead
}}</ref>
!scope="row"| Serbia
| [[Obsolete Serbian units of measurement|Serbian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1874
!scope="row"| Hungary
| [[Hungarian units of measurement|Hungarian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1875
!scope="row" data-sort-value="Turkey" |Ottoman Empire/Turkey
| [[Ottoman units of measurement|Ottoman]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Norway<ref>{{cite web|url=http://www.regjeringen.no/upload/kilde/nhd/hdk/2004/0012/ddd/pdfv/206273-kap_4.pdf|title=Kapittel 4 : Internasjonale avtaler|publisher=Regjeringen.no|access-date=24 November 2014|archive-date=3 December 2014|archive-url=https://web.archive.org/web/20141203101500/http://www.regjeringen.no/upload/kilde/nhd/hdk/2004/0012/ddd/pdfv/206273-kap_4.pdf|url-status=live}}</ref>
| [[Norwegian units of measurement|Norwegian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1876
!scope="row"| [[Metrication in Sweden|Sweden]]
| [[Swedish units of measurement|Swedish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, the previous unit of length ''[[Scandinavian mile|mil]]'', redefined in 1876 as exactly 10&nbsp;km, is however still in informal everyday use for long or approximate distances
|-
!scope="row"| Switzerland
| [[Swiss units of measurement|Swiss]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1878
!scope="row"| Mauritius
| [[Mauritian units of measurement|Mauritian (English, French)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1886
!scope="row"| Finland<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/internat.htm |title=Metric usage and metrication in other countries |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014 |url-status=dead |archive-url=https://web.archive.org/web/19990221223050/http://lamar.colostate.edu/~hillger/internat.htm |archive-date=21 February 1999}}</ref>
| [[Finnish units of measurement|Finnish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1895
!scope="row"| Tunisia
| [[Tunisian units of measurement|Tunisian (Arabic, Turc)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1897
!scope="row"| Madagascar
| [[Malagasy units of measurement|Malagasy]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1899
!scope="row"| Paraguay
| [[Paraguayan units of measurement|Paraguayan (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1907
!scope="row"| Denmark<ref name="CGPM-4-82">{{cite web
 |url          = http://www.bipm.org/utils/common/pdf/CGPM/CGPM4.pdf#page=82
 |title        = Comptes rendus des séances de la quatrième conférence générale des poids et mesures, pages 82-83
 |date         = 1907
 |publisher    = [[International Bureau of Weights and Measures|BIPM]]
 |language     = fr
 |access-date  = 22 November 2021
 |archive-date = 4 December 2020
 |archive-url  = https://web.archive.org/web/20201204112200/https://www.bipm.org/utils/common/pdf/CGPM/CGPM4.pdf#page=82
 |url-status   = live
}}</ref>
| [[Danish units of measurement|Danish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Iceland<ref name="CGPM-4-82" />
| [[Icelandic units of measurement|Icelandic]] / [[Danish units of measurement|Danish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1908
!scope="row"| Costa Rica
| [[Costa Rican units of measurement|Costa Rican (variants of Spanish)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1912
!scope="row"| Dominican Republic
| [[Spanish customary units|Spanish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1918
!scope="row"| Russia<ref name="SovNarkomDecree">
{{cite journal
 |journal      = [[:ru:Собрание узаконений РСФСР]]
 |title        = Metric
 |year         = 1918
 |issue        = 66
 |page         = 725
 |language     = ru
}}</ref><ref name="SovietCalendar1920">
{{Cite book
 | url         = https://books.google.com/books?id=cjQkAQAAIAAJ&q=%D0%BC%D0%B5%D1%82%D1%80%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B0%D1%8F%20%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC%D0%B0&pg=PA8
 | page        = 8
 | year        = 1920
 | script-title=ru:Настольный Советский Календарь
 |trans-title=Desk Soviet Calendar
 | publisher   = The New International Publishing, New York
 | language    = ru
}}</ref>
| [[Obsolete Russian units of measurement|Russian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="3"| 1920
!scope="row"| Poland<ref name="CGPM-6-65" />
| | [[Polish units of measurement|Polish]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Haiti<ref name="CGPM-6-65" />
| [[Haitian units of measurement|Haitian (variants of French)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Greece<ref name="CGPM-6-65" /><br />1959<ref>{{cite web|url=http://www.e-themis.gov.gr/Portal/files/volumes/temp/ΤΟΜΟΣ%205.doc|format=DOC|title=ΕΛΛΗΝΙΚΗ ΔΗΜΟΚΡΑΤΙΑ ΥΠΟΥΡΓΕΙΟ ΕΣΩΤΕΡΙΚΩΝ ΤΜΗΜΑ ΕΚΔΟΣΕΩΝ ΚΑΙ ΓΡΑΜΜΑΤΕΙΑΚΗΣ-ΛΟΓΙΣΤΙΚΗΣ ΕΞΥΠΗΡΕΤΗΣΗΣ : ΔΙΑΡΚΗΣ ΚΩΔΙΚΑΣ ΝΟΜΟΘΕΣΙΑΣ : ΙΔΡΥΤΗΣ – ΔΩΡΗΤΗΣ|website=E-themis.gov.gr|access-date=10 September 2017|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304212526/http://www.e-themis.gov.gr/Portal/files/volumes/temp/%CE%A4%CE%9F%CE%9C%CE%9F%CE%A3%205.doc|url-status=dead}}</ref>
| [[Greek units of measurement|Greek]] and [[Ancient Greek units of measurement|Ancient Greek]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="3"| 1923
!scope="row"| Morocco<ref name="CGPM-7-66" />
| [[Moroccan units of measurement|Moroccan (Arabic, Turc)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Iran<ref name="CGPM-7-66" />
| [[Persian units of measurement|Persian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Thailand<ref>{{cite web
 |url          = http://www.nwmc.go.th/history_eng.html
 |title        = History of weights and measures in Thailand.htm
 |date         = April 2004
 |publisher    = Northern Weights and Measures Center (Thailand)
 |access-date  = 26 September 2011
 |quote        = ..."Weights and Measures Act, [[Thai solar calendar#Buddhist Era|B.E.]] 2466" [1923 A.D.] .... [superseded by ] "Weights and Measures Act, B.E. 2542"  ... Government Gazette, Royal Decree Version, Volume 116, Part 29 a, dated 21 April 1999 ... effective since 18 October 1999
 |archive-date = 2 April 2012
 |archive-url  = https://web.archive.org/web/20120402234248/http://www.nwmc.go.th/history_eng.html
 |url-status   = live
}}</ref><ref>{{cite web
 |url          = http://nwmc.go.th/his1.html
 |script-title = th:ประวัติชั่งตวงวัดไทย
 |date         = April 2004
 |publisher    = Northern Weights and Measures Center (Thailand)
 |language     = th
 |access-date   = 26 September 2011
|archive-url  = https://web.archive.org/web/20120402234248/http://nwmc.go.th/his1.html
 |archive-date = 2 April 2012
|url-status   = dead
}}</ref><ref name="CGPM-7-66">{{cite web
 |url          = http://www.bipm.org/utils/common/pdf/CGPM/CGPM7.pdf#page=68
 |title        = Comptes rendus des séances de la septième conférence générale des poids et mesures, pages 66-69
 |date         = 1927
 |publisher    = [[International Bureau of Weights and Measures|BIPM]]
 |language     = fr
 |access-date  = 5 April 2021
 |archive-date = 4 December 2020
 |archive-url  = https://web.archive.org/web/20201204112012/https://www.bipm.org/utils/common/pdf/CGPM/CGPM7.pdf#page=68
 |url-status   = live
}}</ref>
| [[Thai units of measurement|Thai]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1924
!scope="row"| [[Metrication of Japan|Japan]]<ref>{{citation |last=Mitsuo |first=Tamano |contribution=Japan's Transition to the Metric System |contribution-url=https://books.google.com/books?id=dFLL50miMpgC&pg=PA97 |pages=[https://books.google.com/books?id=dFLL50miMpgC&pg=PA97 97–98] |url=https://books.google.com/books?id=dFLL50miMpgC |date=July 1971 |title=US Metric Study Interim Report, ''No. 3:'' Commercial Weights and Measures |series=National Bureau of Standards Special Publication 345-3 |publisher=US Department of Commerce |location=[[Washington, D.C.|Washington]]}}.</ref><ref name="CGPM-6-65">{{cite web
 |url          = http://www.bipm.org/utils/common/pdf/CGPM/CGPM6.pdf#page=69
 |title        = Comptes rendus des séances de la sixtième conférence générale des poids et mesures, page 65
 |date         = 1921
 |publisher    = [[International Bureau of Weights and Measures|BIPM]]
 |language     = fr
 |access-date  = 5 April 2021
 |archive-date = 4 December 2020
 |archive-url  = https://web.archive.org/web/20201204112030/https://www.bipm.org/utils/common/pdf/CGPM/CGPM6.pdf#page=69
 |url-status   = live
}}</ref>
| [[Japanese units of measurement|Japanese]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, with continued informal use of the [[gō (unit)|gō]] serving size, [[tsubo]] for floorspace.
|-
|1924
!scope="row"| Latvia<ref>{{Cite web |last=Sprūde |first=Viesturs |date=2014-01-02 |title=1924. gada 2. janvārī |trans-title=On 2 January 1924 |url=https://www.la.lv/1924-gada-2-janvari |access-date=2025-10-23 |website=[[LA.LV]] |language=lv}}</ref>
| [[Latvian units of measurement|Latvian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1925s
!scope="row"| China
| [[Chinese units of measurement|Chinese]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric.  Wet markets continue to use ''jin'' ([[catty]]) and ''liang'' for weight, land area is still given in ''[[Mu (area)|mu]]'', and other traditional units (e.g., ''[[Chi (unit)|chi]]'' for length) continue to be used informally in everyday language. The People's Republic of China has defined these units so that conversion factors to SI are simple fractions or whole numbers.  (See the article on [[Chinese units of measurement]] for differences in definitions between the PRC, ROC, and other Sinosphere countries and regions.)    
|-
| 1926
!scope="row"| Afghanistan<ref name="CGPM-7-66" />
| [[Afghan units of measurement|Afghan (Persian, Arab, Indian)]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1929
!scope="row"| Estonia
| [[Estonian units of measurement|Estonian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1946
!scope="row"| Indonesia
| [[Indonesian units of measurement|Indonesian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, however AC units are still measured and advertised in horsepower.<ref>{{cite news |title=Sebelum Pasang AC, Pahami Dulu AC 1 PK Berapa Watt & AC 1/2 PK Berapa Watt! |url=https://artikel.rumah123.com/sebelum-pasang-ac-pahami-dulu-ac-1-pk-berapa-watt-ac-1-2-pk-berapa-watt-52913 |access-date=5 May 2022 |first=Kartika |last=Ratnasari |date=22 March 2022 |work=artikel.rumah123.com |language=id |archive-date=18 May 2022 |archive-url=https://web.archive.org/web/20220518104616/https://artikel.rumah123.com/sebelum-pasang-ac-pahami-dulu-ac-1-pk-berapa-watt-ac-1-2-pk-berapa-watt-52913 |url-status=live }}</ref><ref>{{cite web |title=Definisi PK Dalam AC yang Harus Anda Ketahui |date=21 July 2020 |url=https://cvastro.com/definisi-pk-dalam-ac.htm |access-date=5 May 2022 |publisher=ASTRO |language=id |archive-date=29 May 2022 |archive-url=https://web.archive.org/web/20220529045855/https://cvastro.com/definisi-pk-dalam-ac.htm |url-status=live }}</ref> Informally, floorspace or rural/agrarian land measured differently in each local regions (Sundanese regions tend to use "bata/tumbak", Javanese regions use "ubin/rakit/kesuk/bahu/ru", "rante" in Malay regions, "borong/anggar" in West Kalimantan, "ubin/iring/lupit/tampah" in other regions, etc.).
|-
| 1948
!scope="row"| Israel
| [[Ottoman units of measurement|Ottoman]] and [[Biblical and Talmudic units of measurement|Biblical and Talmudic]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1950
!scope="row"| Somalia
| [[Somali units of measurement|Somali]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1954
!scope="row"| [[Metrication in India|India]]
| [[Indian units of measurement|Indian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Sudan
| Sudanese (various)
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1961
!scope="row"| [[Metrication of South Korea|South Korea]]
| [[Korean units|Korean]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, use of the [[pyeong]] of floorspace is still in use.
|-
|rowspan="3"| 1963
!scope="row"| Ethiopia
| [[Ethiopian units of measurement|Ethiopian]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Laos
| Laotian (various)
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
!scope="row"| Vietnam
| [[Vietnamese units of measurement|Vietnamese]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1965
!scope="row"| [[Metrication in the United Kingdom|United Kingdom]]<ref group="Note">Phased transition announced in 1965</ref>
| [[Imperial units|Imperial]]
| bgcolor="#ECCEF2" data-sort-value="3purple" | Metric and imperial; the metric system is the legislated dominant system of measurement however, legislation for imperial units remains for sales of some goods and speed and distance road signs.
|-
|rowspan="2"| 1967
!scope="row"| [[Metrication in Ireland|Ireland]]
| [[Irish units of measurement|Irish]] then [[Irish measure]] prior to 1824, and [[Imperial units|imperial]].
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, however Draught [[beer]] and [[cider]] are required to be sold by [[imperial pint]]; [[troy ounce]] for precious metals also legal.<ref>{{cite ISB |title=European Communities (Units of Measurement) (Amendment) Regulations 2010 |year=2010|type=si|num=89 |access-date=22 January 2019 |date=2 March 2010|signedby=[[Mary Coughlan (politician)|Mary Coughlan]], [[Minister for Enterprise, Tourism and Employment|Minister for Enterprise, Trade and Employment]]}}</ref> Floor area is still commonly advertised using square feet. 
|-
!scope="row"| Pakistan
| [[History of measurement systems in Pakistan|Pakistani]] and [[Imperial units|imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1969
!scope="row"| [[Metrication in New Zealand|New Zealand]]
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1970
!scope="row"| [[Metrication in Australia|Australia]]
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, (real estate, especially farmland, above a certain size is still frequently advertised in [[hectare]]s or, somewhat less frequently, [[acre]]s. Human weights were traditionally measured in [[stone (weight)|stones]], and this is still in occasional use by older generations; this however is rapidly dying out.)
|-
!scope="row"| [[Metrication in Canada|Canada]]<ref name="Weights and Measures Act (R.S.C., 1985, c. W-6)">{{cite web
 |url          = http://laws-lois.justice.gc.ca/eng/acts/W-6/
 |title        = Weights and Measures Act
 |year         = 1985
 |work         = Chapter 36 Section 7
 |publisher    = Minister of Justice
 |access-date  = 24 May 2018
 |archive-date = 25 April 2011
 |archive-url  = https://web.archive.org/web/20110425193128/http://laws-lois.justice.gc.ca/eng/acts/W-6/
 |url-status   = live
}}</ref>
| [[Weights and Measures Act (Canada)|Imperial]]
| bgcolor="#ECCEF2" data-sort-value="3purple" | Metric and imperial (body measurements are referred to in imperial units, and certain industries such as real estate, construction, and home appliances still use imperial measurements due to a high reliance on American manufacturing.) Metrication was halted in 1985.<ref>{{cite web
 |url=http://www.thecanadianencyclopedia.ca/en/article/metric-conversion/
 |title=Metric Conversion
 |author=Dr. Natarajan Ganapathy
 |year=2009
 |work=Science & Medicine
 |publisher=The Canadian Encyclopedia
 |access-date=11 July 2022
 |archive-date=29 April 2018
 |archive-url=https://web.archive.org/web/20180429220637/http://www.thecanadianencyclopedia.ca/en/article/metric-conversion/
 |url-status=live
 }}</ref>
|-
|rowspan="2"| 1971
!scope="row"| Singapore<ref>{{Cite web |title=Metrication in Singapore |url=https://www.nlb.gov.sg/main/article-detail?cmsuuid=7790f5e5-f6f0-4e1e-800d-88d0509bc5b0 |access-date=9 November 2023 |website=www.nlb.gov.sg |archive-date=9 November 2023 |archive-url=https://web.archive.org/web/20231109110150/https://www.nlb.gov.sg/main/article-detail?cmsuuid=7790f5e5-f6f0-4e1e-800d-88d0509bc5b0 |url-status=live }}</ref>
| [[Malay units of measurement|Malay]] and [[Imperial units|imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric (land and property areas are still at times measured with [[square foot]] or [[hectare]])
|-
!scope="row"| South Africa<ref group="Note">Including South-West Africa, now [[Namibia]]</ref>
| [[South African units of measurement|South African]] and [[Imperial units|imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1972
!scope="row"| Malaysia
| [[Malay units of measurement|Malay]] and [[Imperial units|imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, with some traditional [[wet markets]] and [[pasar pagi]] still using the [[Malay units of measurement|Malay units]]. [[Imperial units]] are widely used such as size of the real estate are often denoted by square feet rather than square metres.
|-
|rowspan="3"| 1975
!scope="row"| [[Metrication in the United States|United States of America]]<ref group="Note">The metric system was lawfully recognized and permitted for all purposes nationwide by the [[Metric Act of 1866]]. The [[Metric Conversion Act]], which established a federal program to facilitate voluntary metrication, was passed in 1975. In 1988, the Metric Conversion Act was amended to officially recognize the SI as “the preferred system of weights and measures for United States trade and commerce”.</ref><ref name="CIA The World Factbook">{{cite web
 |url          = https://www.cia.gov/library/publications/the-world-factbook/appendix/appendix-g.html
 |title        = CIA The World Factbook
 |year         = 2010
 |work         = Appendix G: Weights and Measures
 |publisher    = US Central Intelligence Agency
 |access-date  = 14 August 2013
 |archive-date = 6 April 2011
 |archive-url  = https://web.archive.org/web/20110406124728/https://www.cia.gov/library/publications/the-world-factbook/appendix/appendix-g.html
 |url-status   = dead
}}</ref>
| [[United States customary units]]
| bgcolor="#ECCEF2" data-sort-value="3purple" | Metric and US customary System. The US customary system remains the dominant system of measurement.
|-
!scope="row"| [[Metrication of North Korea|North Korea]]<ref>{{citation |ref={{harvid|APLMF|2015}} |contribution=DPR Korea |contribution-url=http://www.aplmf.org/dpr-korea.html |title=''Official site'' |url=http://www.aplmf.org/ |publisher=Asia–Pacific Legal Metrology Forum |date=2015 |access-date=6 June 2017 |archive-date=9 February 2017 |archive-url=https://web.archive.org/web/20170209124429/http://www.aplmf.org/ |url-status=live }}.</ref>
| [[Korean units|Korean]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, with formal continued use of [[Korean units|traditional units]]<ref>{{citation |ref={{harvid|DPRK|1993}} |title=''"The Law of the Democratic People's Republic of Korea on Metrology"'' |url=http://www.keikoren.or.jp/measure/20130703-4.pdf |series=No. 484-112 |date=3 February 1993 |publisher=Supreme People's Assembly of the DPRK |location=Pyongyang |access-date=6 June 2017 |archive-date=8 January 2019 |archive-url=https://web.archive.org/web/20190108105032/http://www.keikoren.or.jp/measure/20130703-4.pdf |url-status=dead }}. {{in lang|ko}}{{nbsp}}& {{in lang|en}}</ref><ref>{{citation |ref={{harvid|TEG|2017}} |title=The Economist Intelligence Unit |contribution=North Korea: Summary |contribution-url=http://country.eiu.com/article.aspx?articleid=485115232&Country=North%20Korea&topic=Summary&subtopic=Basic+data |date=10 February 2017 |location=London |publisher=The Economist Group |access-date=6 June 2017 |archive-date=8 August 2020 |archive-url=https://web.archive.org/web/20200808170630/http://country.eiu.com/article.aspx?articleid=485115232&Country=North%20Korea&topic=Summary&subtopic=Basic+data |url-status=live }}.</ref>
|-
!scope="row"| Ghana<ref>{{cite news |title=Ghana Gets Metric System |url=https://www.nytimes.com/1975/09/03/archives/ghana-gets-metric-system.html |work=The New York Times |date=3 September 1975 |access-date=18 October 2019 |archive-date=18 October 2019 |archive-url=https://web.archive.org/web/20191018114735/https://www.nytimes.com/1975/09/03/archives/ghana-gets-metric-system.html |url-status=live }}</ref>
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
|rowspan="2"| 1976
!scope="row"| Sri Lanka<ref>{{cite web |url=http://www.commonlii.org/lk/legis/consol_act/nmc189324.pdf |title=Numerical Metric Conversion |website=Commonwealth Legal Information Institute |access-date=10 September 2017 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304062941/http://www.commonlii.org/lk/legis/consol_act/nmc189324.pdf |url-status=live }}</ref>
| [[Sri Lankan units of measurement|Sri Lankan]] and [[Imperial units|imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric<ref>{{cite web |url=http://archives.dailynews.lk/2006/03/06/main_Letters.asp |title=-- Letters |website=Daily News |location=Cyprus |access-date=10 September 2017 |archive-date=10 January 2014 |archive-url=https://web.archive.org/web/20140110171539/http://archives.dailynews.lk/2006/03/06/main_Letters.asp |url-status=live }}</ref>
|-
!scope="row"| [[Hong Kong units of measurement|Hong Kong]]
| [[Imperial units|Imperial]], [[Chinese units of measurement|Chinese]]
| bgcolor="#CEE6F2" data-sort-value="1blue"  | Metric is the legislated dominant system of measurement, however [[Chinese units of measurement|Chinese units]] and [[imperial units]] are still legal under Weights and Measures Ordinance. The usage of [[Chinese units of measurement|Chinese units]] or [[imperial units]] are still common on fresh food sales (e.g. [[wet markets]]), and real estates still use [[square foot]] as area measurement unit.
|-
| 1984
!scope="row"| Taiwan
| [[Taiwanese units of measurement|Taiwanese]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric (traditional [[wet markets]] and real estate still use [[Taiwanese units of measurement|Taiwanese units]].)
|-
| 1992
!scope="row"| [[Chinese units of measurement#Macau|Macau]]
| [[Imperial units|Imperial]], [[Chinese units of measurement|Chinese]] (also [[United States customary units]])
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| 1998
!scope="row"| [[Metrication in Jamaica|Jamaica]]
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, On 10 June 2015, the Jamaican government passed the Road Traffic Bill 2014, which formally repealed and replaced the Road Traffic Act and Regulations 1938. The act included updates to Jamaica's traffic laws along with the use of the metric system within regulatory descriptions. On 18 September 2015, the Jamaican government amended the Weights and Measure Act to include considerable fines to business owners who do not use the metric system.
|-
| 2004
!scope="row"| Trinidad and Tobago
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, in 2004 Trinidad and Tobago passed legislation making the International System of Units shall be the primary system of measurement in Trinidad and Tobago in 2015.
|-
| 2005
!scope="row"| Saint Lucia
| [[Imperial units|Imperial]]
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric
|-
| data-sort-value="9999" | Indeterminate
!scope="row"| Liberia<ref group="Note">See also [[Liberia#Measurement system|Liberia measurement system]].</ref>
|[[Imperial units|United States customary units]]<ref name="CIA The World Factbook"/>
| bgcolor="#ECCEF2" data-sort-value="3purple" | Metric and imperial. The Liberian government has begun transitioning from use of imperial units to the metric system.  However, this change has been gradual, with government reports concurrently using both systems.<ref>{{cite web
 |url=http://trend.ag.utk.edu/international/ReformingCocoaCoffeeMarketingLiberia.pdf 
 |title=Reforming Cocoa and Coffee Marketing in Liberia 
 |first=Michael D. |last=Wilcox, Jr. Department of Agricultural Economics University of Tennessee 
 |year=2008 
 |work=Presentation and Policy Brief 
 |publisher=University of Tennessee 
 |access-date=25 April 2010 |url-status=dead 
 |archive-url=https://web.archive.org/web/20100624032539/http://trend.ag.utk.edu/international/ReformingCocoaCoffeeMarketingLiberia.pdf 
 |archive-date=24 June 2010}}</ref>
|-
| data-sort-value="2013" | 2011<ref group="Note">In June 2011, the Myanmar government's Ministry of Commerce began discussing proposals to reform the measurement system in Myanmar and adopt the metric system used by most of its trading partners.</ref><ref>{{cite news
 | url         = http://www.mmtimes.com/2011/business/584/biz58401.html
 | archive-url  = https://web.archive.org/web/20130528014209/http://www.mmtimes.com/2011/business/584/biz58401.html
 | archive-date = 28 May 2013
 | title       = Ditch the viss, govt urges traders
 | author      = Ko Ko Gyi
 | newspaper   = The Myanmar Times
 | date        = 18–24 July 2011
 | access-date  = 14 August 2013
}}</ref><br />2013<ref>{{cite web
|url = http://www.elevenmyanmar.com/national/3684-myanmar-to-adopt-metric-system
|title = Myanmar to adopt metric system
|publisher = [[Eleven Media Group]]
|date = 10 October 2013
|archive-url = https://web.archive.org/web/20131220152124/http://elevenmyanmar.com/national/3684-myanmar-to-adopt-metric-system
|archive-date = 20 December 2013
|url-status = dead
|access-date = 20 April 2015}}</ref><ref>{{cite web |url=https://metricviews.org.uk/2018/02/metric-in-myanmar-an-update/ |title=Metric in Myanmar - an update |date=8 February 2018 |website=Metric Views |publisher=UK Metric Association |access-date=24 February 2020 |archive-url=https://web.archive.org/web/20190619235513/http://metricviews.org.uk/2018/02/metric-in-myanmar-an-update/ |archive-date=19 June 2019 |url-status=dead}}</ref>
!scope="row"| Myanmar
| [[Burmese units of measurement|Burmese]] and [[Imperial units|imperial]]
| bgcolor="#ECCEF2" data-sort-value="3purple" | Metric and imperial,<ref>{{cite news
 | url         = http://mmtimes.com/index.php/business/property-news/1041-workshop-to-mull-new-weight-and-measurement-standards.htm
 | title       = Workshop to mull new weight and measurement standards
 | author      = Htar Htar Khin
 | newspaper   = The Myanmar Times
 | date        = 20 February 2012
| access-date  = 14 August 2013
}}{{dead link|date=May 2016|bot=medic}}{{cbignore|bot=medic}}</ref>  Announcement of full metrication in 2014, with technical assistance from the [[Physikalisch-Technische Bundesanstalt|German National Metrology Institute]].<ref>{{cite news|url= http://mizzima.com/opinion/features/item/10955-metrication-in-myanmar |title=  Metrication in Myanmar |website= [[Mizzima News]] |first= Nicholas |last= Kohler |date= 3 March 2014 |archive-url= https://web.archive.org/web/20141216042534/http://mizzima.com/opinion/features/item/10955-metrication-in-myanmar |archive-date= 16 December 2014 |url-status= dead | access-date= 20 April 2015}}</ref> Distances and speed limits on road signs are shown in kilometres (per hour), and height clearance signs are shown in metres; fuel is measured and sold in litres; and meteorological data and weather reports are shown in degrees Celsius for temperatures, millimetres for precipitation and kilometres per hour for wind speed.
|-
|2015
!scope="row"|Samoa
|Traditional units
| bgcolor="#CEE6F2" data-sort-value="1blue" | Metric, The Metrology Act 2015 mandates the use of metric/SI units in trade, with a transition period of one year.<ref name="samoa">{{Cite web |url=https://www.mcil.gov.ws/wp-content/uploads/2018/07/Metrology-Act-2015.pdf |title=Metrology Act 2015 |publisher=Ministry of Commerce, Industry and Labour of the Government of Samoa |language=en |date=2016 |accessdate=2024-06-10 |archive-date=7 June 2024 |archive-url=https://web.archive.org/web/20240607165836/https://www.mcil.gov.ws/wp-content/uploads/2018/07/Metrology-Act-2015.pdf |url-status=dead }}</ref>
|}
'''Notes'''
{{reflist|group=Note}}

== Methods of conversion ==
There are three common ways that nations convert from traditional measurement systems to the metric system. The first is the quick or "Big-Bang" route. The second way is to phase in units over time and progressively outlaw traditional units. This method, favoured by some [[industrial nation]]s, is slower and generally less complete. The third way is to redefine traditional units in metric terms. This has been used successfully where traditional units were ill-defined and had regional variations.

The "Big-Bang" way is to simultaneously outlaw the use of [[history of measurement|pre-metric]] measurement, metricate, reissue all government publications and laws, and change education systems to metric. [[India]] was the first Commonwealth country to use this method of conversion. Its changeover lasted from 1 April 1960, when metric measurements became legal, to 1 April 1962, when all other systems were banned. The Indian model was extremely successful and was copied over much of the developing world.<ref>{{Cite web |title=Metrication in other countries |url=https://usma.org/metrication-in-other-countries#india |date=2020-08-03 |url-status=live |archive-url=https://web.archive.org/web/20250226121612/https://usma.org/metrication-in-other-countries#india |archive-date=2025-02-26 |access-date=2025-11-09 |website=US Metric Association}}</ref> Two industrialized Commonwealth countries, Australia and [[New Zealand]], also did a quick conversion to metric.

The phase-in way is to pass a law permitting the use of metric units in parallel with traditional ones, followed by education of metric units, then progressively ban the use of the older measures.  This has generally been a slow route to metric.  The [[British Empire]] permitted the use of metric measures in 1873, but the changeover was not completed in most Commonwealth countries other than India and Australia until the 1970s and 1980s when governments took an active role in metric conversion.  In the United Kingdom and Canada, the process is still incomplete.  Japan also followed this route and did not complete the changeover for 70&nbsp;years.  By law, loose goods sold with reference to units of quantity have to be weighed and sold using the metric system.  In 2001, the EU directive [[Units of Measure Directive|80/181/EEC]] stated that supplementary units (imperial units alongside metric including labelling on packages) would become illegal from the beginning of 2010.  In September 2007,<ref name="EUGivesUp"/> a consultation process was started which resulted in the directive being modified to permit supplementary units to be used indefinitely.

The third method is to redefine traditional units in terms of metric values.  These redefined "quasi-metric" units often stay in use long after metrication is said to have been completed.  Resistance to metrication in post-revolutionary France convinced Napoleon to revert to ''[[mesures usuelles]]'' (usual measures), and, to some extent, the names remain throughout Europe.  In 1814, Portugal adopted the metric system, but with the names of the units substituted by [[Portuguese customary units|Portuguese traditional ones]].  In this system, the basic units were the ''mão-travessa'' (hand) = 1&nbsp;[[decimetre]] (10&nbsp;''mão-travessas'' = 1&nbsp;''vara'' (yard) = 1&nbsp;metre), the ''[[canada (volume)|canada]]'' = 1&nbsp;litre and the ''libra'' (pound) = 1&nbsp;kilogram.<ref name=Fatima />  In the [[Netherlands]], 500&nbsp;g is informally referred to as a ''pond'' ([[Pound (mass)|pound]]) and 100&nbsp;g as an ''ons'' ([[ounce]]), and in Germany and France, 500&nbsp;g is informally referred to respectively as ''ein Pfund'' and ''une livre'' ("one pound").<ref>
{{cite web 
 |author=Hubert Fontaine 
 |title=Confiture de rhubarbe 
 |url=http://www.hubertlejardinier.com/confiture.htm 
 |access-date=5 November 2007 |archive-url=https://web.archive.org/web/20070928081538/http://www.hubertlejardinier.com/confiture.htm 
 |archive-date=28 September 2007 |language=fr 
 |url-status=dead 
}} "1 zeste de citron par livre (500g) de rhubarbe"</ref>

In Denmark, the re-defined ''pund'' (500&nbsp;g) is occasionally used, particularly among older people and (older) fruit growers, since these were originally paid according to the number of pounds of fruit produced.  In [[Sweden]] and [[Norway]], a ''mil'' ([[Scandinavian mile]]) is informally equal to 10&nbsp;km, and this has continued to be the predominantly used unit in conversation when referring to geographical distances.  In the 19th century, [[Switzerland]] had a non-metric system completely based on metric terms (e.g. 1&nbsp;''Fuss'' (foot) = 30&nbsp;cm, 1&nbsp;''Zoll'' (inch) = 3&nbsp;cm, 1&nbsp;''Linie'' (line) = 3&nbsp;mm).  In China, the ''[[catty|jin]]'' now has a value of 500&nbsp;g and the [[tael|liang]] is 50&nbsp;g.

Surveys are performed by various interest groups or the government to determine the degree to which ordinary people change to using metric in their daily lives. In countries that have recently changed, older segments of the population tend still to use the older units.<ref>{{Cite web |title=Metric or imperial: what measures do Britons use? {{!}} YouGov |url=https://yougov.co.uk/society/articles/41755-metric-or-imperial-what-measures-do-britons-use?redirect_from=%2Ftopics%2Fsociety%2Farticles-reports%2F2022%2F04%2F07%2Fmetric-or-imperial-what-measures-do-britons-use |access-date=2024-06-27 |website=yougov.co.uk |language=en-gb}}</ref>

== Industries and countries resistant to metrication ==
[[File:1 oz of fine gold.jpg|thumb|upright=0.75|Precious metals, such as gold, are often measured in troy ounces.]]
{{As of|2024}}, the metric system predominates in most of the world, however specific industries are more resistant to metrication. For example:

=== Manufacturing and engineering ===
*Photograph and video cameras are standardised to mount to tripods using {{1/4}}-20 and {{frac|3|8}}-16 screws, which are dimensioned in inches, by ISO 1222:2010.<ref>{{cite web|url=http://webstore.ansi.org/FindStandards.aspx?SearchString=ISO+1222:2010&SearchOption=0&PageNum=0&SearchTermsArray=null%7CISO+1222:2010%7Cnull|title=Find Standards using keywords and publication number|first=American National Standards Institute|last=ANSI|website=ANSI Webstore|access-date=10 September 2017|archive-date=11 September 2017|archive-url=https://web.archive.org/web/20170911071807/https://webstore.ansi.org/FindStandards.aspx?SearchString=ISO+1222%3a2010&SearchOption=0&PageNum=0&SearchTermsArray=null%7cISO+1222%3a2010%7cnull|url-status=live}}</ref>
*[[Thread count]] is frequently measured in threads per inch.<ref>{{Cite web |date=2017-03-10 |title=What is threadcount? – domus home |url=https://www.domus-home.com/bed-linen/threadcount/ |access-date=2023-11-18 |quote=Thread count is typically quoted using the Imperial system of 1 square inch, whilst the Metric system (mainly used in Australia and New Zealand) is based upon 10 square centimeters. Suppose you pick up a bedsheet package that quotes 200 threadcount per square inch (2.54&nbsp;cm × 2.54&nbsp;cm). Let's say that is made up of 100 threads along the length of 2.54&nbsp;cm, plus 100 threads along the width of 2.54&nbsp;cm. Since 10 square centimetres is 3.16&nbsp;cm × 3.16&nbsp;cm, this equates to 124 threads along the 3.16&nbsp;cm length, plus 124 threads along the 3.16&nbsp;cm width. Threadcount per 10&nbsp;sq&nbsp;cm is therefore 124+124, which rounds up to 250. |archive-date=18 November 2023 |archive-url=https://web.archive.org/web/20231118102930/https://www.domus-home.com/bed-linen/threadcount/ |url-status=live }}</ref>
* [[Abrasive]]s, such as [[sandpaper]] and [[sharpening stone]]s, are commonly graded by grit, corresponding to the level of abrasiveness ([[mesh (scale)|mesh]] size) per square inch.

=== Computers and televisions ===
* [[Dots per inch]] and [[Pixel density|pixels per inch]] are still used to describe graphical resolution with computers and printing.
* [[Areal density (computer storage)|Data density]] for [[magnetic tape data storage]] is measured in bits per inch for density and bits per square inch for area density.<ref>{{cite magazine|url=https://spectrum.ieee.org/why-the-future-of-data-storage-is-still-magnetic-tape|magazine=[[IEEE Spectrum]]|quote=Combining these technologies, we were able to read and write data in our laboratory system at a linear density of 818 000/in. For historical reasons, tape engineers around the world measure data density in inches. In combination with the 246 200 tracks per inch that the new technology can handle, our prototype unit achieved an area density of 201 gigabits per square inch.|title=Why the Future of Data Storage is (Still) Magnetic Tape|date=28 August 2018|first=Mark|last=Lantz|access-date=11 December 2020|archive-date=8 January 2021|archive-url=https://web.archive.org/web/20210108150035/https://spectrum.ieee.org/computing/hardware/why-the-future-of-data-storage-is-still-magnetic-tape|url-status=live}}</ref>
* Digital [[display size]]s are usually advertised diagonally, using inches, along with centimetres supplementarily.
* [[Photographic paper]] are still sold with imperial [[Photo print sizes|print sizes]] across the world in metric countries.<ref>{{Cite web |last=Bester |first=Danie |date=2018-10-16 |title=Standard Print Sizes |url=https://digitalphotographycourses.co.za/standard-print-sizes/ |access-date=2023-11-18 |website=DPC {{!}} Digital Photography Courses |archive-date=18 November 2023 |archive-url=https://web.archive.org/web/20231118222149/https://digitalphotographycourses.co.za/standard-print-sizes/ |url-status=live }}</ref>
* The dominant [[Pin header|pin spacing]] for electronic components is based on {{convert|1/10|in|mm|2|abbr=on}}.

=== Consumer goods ===
* Surfboards are usually designed, constructed, and sold in feet and inches.<ref>{{cite web |title=How to choose the right surfboard: Ultimate Guide |url=https://www.surfnation.com.au/pages/how-to-choose-the-right-surfboard |access-date=2023-11-18 |website=Surf Nation}}</ref>
* [[Shoe size|Shoes]] are still sold by the [[Barleycorn (unit)|barleycorn]] in most English speaking countries, or the [[Paris point|Paris Point]] in Europe.
* The [[fill power]] of [[down feather]] insulation is commonly expressed in "cubic inches per ounce".
* [[Precious metal]]s are often sold in troy ounces, even in mostly metric states.<ref>{{cite web|url=https://www.perthmint.com/education_uom.aspx|work=[[Perth Mint]]|date=n.d.|access-date=23 January 2019|title=Units of Measurement|archive-date=7 June 2019|archive-url=https://web.archive.org/web/20190607051942/https://www.perthmint.com/education_uom.aspx|url-status=dead}}</ref>

=== Land, area and distances on the ground ===
* [[Golf course]]s are measured in [[yard]]s in the United States, Canada, Japan, South Korea, China, Thailand, the Philippines, Venezuela, Colombia, the Dominican Republic, Indonesia, Vietnam, and Cambodia. In the United Kingdom and Ireland, some golf courses are measured in yards while others are measured in metres.
* Office space and housing space is often sold and rented in [[Square foot|square feet]] in Hong Kong, Singapore, Malaysia, Canada and India, [[square yard]]s in India, Pakistan and Bangladesh, and ''[[tsubo]]''/''[[pyeong]]''/"[[pyeong#Ping|ping]]" in Japan, Korea, and Taiwan.

=== Road and rail transportation ===
* Road signs for distance and speed limit are still displayed in yards, miles and [[miles per hour]] in the United States, United Kingdom, and multiple Caribbean nations.
* [[Tyre pressure]] is commonly measured in [[Pound-force per square inch|pounds per square inch]] in multiple countries, including Argentina, Australia, Brazil, Canada, Chile, India, Ireland, Mexico, Peru, the United Kingdom, and the United States.
* Car and bicycle rim diameters are still usually set as whole inch measurements, and tyre widths are measured in millimetres.
* Engine power is usually measured in [[horsepower]] in most former [[Soviet Union|USSR]] countries and German-speaking countries (this is [[Horsepower#PS|metric horsepower]] rather than mechanical horsepower), although in the EU from 2010 the horsepower is permitted only as a supplementary unit.<ref>{{cite web|url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:114:0010:0013:EN:PDF|format=PDF|title=Directive 2009/3/EC of the European Parliament and of the Council of 11 March 2009|work=Official Journal of the European Union|access-date=5 February 2015|archive-date=4 September 2015|archive-url=https://web.archive.org/web/20150904003318/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:114:0010:0013:EN:PDF|url-status=live}}</ref> 
* Imperial [[gallon]]s are still used for the sale of fuel in four British Overseas Territories – Anguilla, the British Virgin Islands, the Cayman Islands and Montserrat – and in six countries: Antigua and Barbuda, Dominica, Grenada, Saint Christopher and Nevis, Saint Lucia, and Saint Vincent and the Grenadines.
* United States [[gallon]]s are still used for the sale of fuel in the United States and its territories (except for Puerto Rico, which has used litres since 1980), the three associated countries of the United States (the Federated States of Micronesia, the Marshall Islands and Palau), and in four other countries: Belize, Colombia, Haiti and Liberia.
* Both imperial gallons and United States gallons are used for the sale of fuel in the British Overseas Territory of the Turks and Caicos Islands and in the Bahamas.

=== Air and sea transportation ===
{{Globalise|section|date=September 2008}}
Air and sea transportation commonly use the [[nautical mile]]. This is about one [[minute of arc]] of [[latitude]] along any [[meridian arc]] and it is precisely defined as 1,852 metres (about 1.151 [[mile]]s). It is not an [[International System of Units|SI]] unit. The prime unit of [[speed]] or [[velocity]] for maritime and air navigation remains the [[knot (unit)|knot]] (nautical mile per hour).

The prime unit of measure for aviation (altitude, or [[flight level]]) is usually estimated based on air pressure values, and in many countries, it is still described in nominal feet, although many others employ nominal metres. <!--A vertical spacing of {{convert|1000|ft|m|0}} has become the standard measure for safety and clarity for purposes of air traffic control.{{Citation needed|date=October 2009}}--> The policies of the [[International Civil Aviation Organization]] (ICAO) relating to measurement are:
* there should be a single system of units throughout the world
* the single system should be the SI
* the use of the foot for altitude is a permitted variation.

Consistent with ICAO policy, aviation has undergone a significant amount of metrication over the years. For example, runway lengths are usually given in metres. The United States metricated the data interchange format ([[METAR]]) for temperature reports in 1996, and since indicates temperature in [[Celsius]].<ref>{{cite web|publisher=National Weather Service METAR/TAF Information|url=http://www.nws.noaa.gov/oso/oso1/oso12/faq.htm|title=Frequently Asked Questions about METAR/SPECI and TAF|access-date=21 August 2009|archive-date=20 February 2009|archive-url=https://web.archive.org/web/20090220145833/http://www.nws.noaa.gov/oso/oso1/oso12/faq.htm|url-status=live}}</ref> Metrication is also gradually taking place in cargo mass and dimensions and in fuel volume and mass.

In former Soviet countries and China, the metric system is used in aviation (whereby in Russia altitudes above the [[transition level]] are given in feet).<ref>{{cite web |url=https://aerosavvy.com/metric-imperial/ |access-date=20 October 2023 |title=Aviation's Crazy, Mixed Up Units of Measure |work=AeroSavvy |date=5 September 2014 |archive-date=7 December 2019 |archive-url=https://web.archive.org/web/20191207230641/http://aerosavvy.com/metric-imperial/ |url-status=live }}</ref><ref>{{cite web |url=https://aviation.stackexchange.com/questions/2572/why-doesnt-the-aviation-industry-use-si-units |title=Why doesn't the aviation industry use SI units? |work=Aviation StackExchange |access-date=20 October 2023 |date=22 March 2014 |archive-date=4 July 2018 |archive-url=https://web.archive.org/web/20180704153217/https://aviation.stackexchange.com/questions/2572/why-doesnt-the-aviation-industry-use-si-units |url-status=live }}</ref> Sailplanes use the metric system in many European countries.

In 1975, the assembly of the [[International Maritime Organization]] (IMO) decided that future conventions of the [[SOLAS Convention|International Convention for the Safety of Life at Sea]] (SOLAS) and other future IMO instruments should use SI units only.<ref>{{cite journal |url=http://www.imo.org/blast/blastDataHelper.asp?data_id=24097&filename=351(IX).pdf|title=Resolution A.351(IX) Use of metric units in the SI system in the International Convention for the Safety of Life at Sea, 1974, and other future instruments|journal=Assembly Resolutions|date=12 November 1975|access-date=4 September 2012|publisher=[[International Maritime Organization]]|archive-date=28 August 2013|archive-url=https://web.archive.org/web/20130828012541/http://www.imo.org/blast/blastDataHelper.asp?data_id=24097&filename=351(IX).pdf|url-status=dead}}</ref>

=== Legacy of previous units ===
* In Australia, pints are still used for beer, though a pint has been redefined to be 570 ml (see ''[[Australian beer#Beer glasses|Australian beer glasses]]'').
* [[McDonald's]] sells ''[[Quarter Pounder]]s'' under their original name in all English-speaking countries despite metrication. In the Netherlands and Finland, it is known as a ''Quarter Pounder Cheese'' while Sweden also refers to it as ''QP Cheese''. In [[Quebec]], it is called a ''Quart de livre''. In Latin America and Spain, it is called ''Cuarto de Libra con Queso''. In Taiwan, it is known as the ''four-ounce beef burger''.
* Inch-based spare parts are occasionally kept to service American and pre-1950s machines, but screws are changed to [[metric thread]] at maintenance.
* In [[plumbing]], some pipes and pipe threads are still designated in inch sizes due to historic international acceptance of particular sequences of pipe sizes and pipe threads, such as [[British Standard Pipe|BSP/ISO 7/EN 10226]] threads.
[[File:Metric length shower hose with imperial fittings.jpg|thumb|upright=0.75|A shower hose sold in Germany with metric length (150 cm) and imperial (1/2 in) fittings]]

=== United Kingdom ===
{{See also|Metrication in the United Kingdom}}
In the United Kingdom, some of the population continues to resist metrication to varying degrees. The traditional imperial measures are preferred by a majority and continue to have widespread use in some applications.<ref>{{cite web |title=Will British people ever think in metric? |url=https://www.bbc.co.uk/news/magazine-16245391 |access-date=24 February 2012 |work=BBC News |date=21 December 2011 |author=Jon Kelly |quote=...but today the British remain unique in Europe by holding onto imperial weights and measures. ...&nbsp;the persistent British preference for imperial over metric is particularly noteworthy&nbsp;... |archive-date=24 April 2012 |archive-url=https://web.archive.org/web/20120424232814/http://www.bbc.co.uk/news/magazine-16245391 |url-status=live }}</ref><ref>{{cite news|title=In the merry old land of lb and oz|newspaper=[[The Times]]|date=10 May 2007|author=Melanie McDonagh|quote=A survey from the British Weights and Measures Association, admittedly a partial source, suggested that 80 per cent of people prefer imperial to metric and 70 per cent, including, remarkably, 18- to 24-year-olds, can make sense of weights only in imperial measurements.|url=https://www.thetimes.com/comment/register/article/in-the-merry-old-land-of-lb-and-oz-8s05g6xvgn7|url-access=subscription|access-date=13 August 2022|archive-date=13 August 2022|archive-url=https://web.archive.org/web/20220813153825/https://www.thetimes.co.uk/article/in-the-merry-old-land-of-lb-and-oz-8s05g6xvgn7|url-status=live}}</ref> The metric system is used by most businesses,<ref>{{cite report
 |url          = http://ukma.org.uk/sites/default/files/met1980.pdf
 |title        = Final Report of the Metrication Board (1980)
 |at           = para 1.6 & 1.10
 |publisher    = Department of Trade and Industry Consumer and Competition Policy Directorate
 |location     = London
 |access-date  = 29 June 2012
 |archive-url  = https://web.archive.org/web/20130501034405/http://ukma.org.uk/sites/default/files/met1980.pdf
 |archive-date = 1 May 2013
 |url-status     = dead
 |df           = dmy-all
}}</ref> and is used for most trade transactions. Metric units must be used for certain trading activities (selling by weight or measure for example), although imperial units may continue to be displayed in parallel.<ref name="bl">{{cite web |url=https://www.gov.uk/guidance/national-regulation-weights-and-measures |title=Weights and measures legislation – hallmarking and metrication |work=Business Link |publisher=UK Government |access-date=24 February 2015 |archive-date=14 February 2017 |archive-url=https://web.archive.org/web/20170214083750/https://www.gov.uk/guidance/national-regulation-weights-and-measures |url-status=live }}</ref>

British law has enacted the provisions of [[European units of measurement directives|European Union directive 80/181/EEC]], which catalogues the units of measure that may be used for "economic, public health, public safety and administrative purposes".<ref>{{cite web|url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/250658/0272.pdf |url-status=live |title=Weights and Measures Report 1995 – 2008|publisher=National Weights and Measures Laboratory|archive-url=https://web.archive.org/web/20180705005001/https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/250658/0272.pdf |access-date=24 November 2014|archive-date=5 July 2018}}</ref> These units consist of the recommendations of the [[General Conference on Weights and Measures]],<ref name=SIBrochure/> supplemented by some additional units of measure that may be used for specified purposes.<ref>{{cite web
| url = http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1980L0181:20000209:EN:PDF
| author = The Council of the European Communities
| title = Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC
| date = 9 February 2000
| access-date = 28 October 2011
| archive-date = 23 August 2011
| archive-url = https://web.archive.org/web/20110823031027/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1980L0181:20000209:EN:PDF
| url-status = live
}}</ref> Metric units could be legally used for trading purposes for nearly a century before [[Metrication in the United Kingdom|metrication efforts]] began in earnest. The government had been making preparations for the conversion of the [[imperial unit]] since the 1862 ''Select Committee on Weights and Measures'' recommended the conversion<ref>{{cite web|publisher=Department of Trade and Industry, United Kingdom |year=1862 |url=http://www.metric.org.uk/Docs/DTI/met1862.pdf |title=Report (1862) from the Select Committee on Weights and Measures |access-date=23 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090609211239/http://www.metric.org.uk/Docs/DTI/met1862.pdf |archive-date=9 June 2009}}</ref> and the [[Metric Weights and Measures Act 1864]] ([[27 & 28 Vict.]] c. 117) and the [[Weights and Measures (Metric System) Act 1897]] ([[60 & 61 Vict.]] c. 46) legalised the metric system.<ref>{{cite web |url=http://www.metric.org.uk/Press/metrictimeline.aspx |title=Metrication Timeline |website=[[UK Metric Association]] |year=2008 |access-date=23 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090608034304/http://www.metric.org.uk/press/metrictimeline.aspx |archive-date=8 June 2009}}</ref>

In 1965, with lobbying from British industries and the prospects of joining the [[European Community|Common Market]], the government set a 10-year target for full conversion, and created the [[Metrication Board]] in 1969. Metrication occurred in some areas during this time period, including the re-surveying of [[Ordnance Survey]] maps in 1970, [[decimalisation]] of the [[Pound sterling|currency]] in 1971, and teaching the metric system in schools. No plans were made to make the use of the metric system compulsory, and the Metrication Board was abolished in 1980 following a [[1979 United Kingdom general election|change in government]].<ref>{{cite web |author=Jim Humble |url=http://www.metric.org.uk/Press/Articles.aspx?ID=7 |date=12 December 2002 |title=Historical perspectives by the last Director of the UK Metrication Board |website=[[UK Metric Association]] |access-date=27 May 2009 }}{{dead link|date=July 2024|bot=medic}}{{cbignore|bot=medic}}</ref>

The United Kingdom avoided having to comply with the 1989 European Units of Measurement Directive (89/617/EEC), which required all member states to make the metric system compulsory, by negotiating [[derogation]]s (delayed switchovers), including for miles on road signs and for pints for draught beer, cider, and milk sales.<ref>{{cite report
 |url=https://www.legislation.gov.uk/uksi/1995/1804/contents/made
 |title=The Units of Measurement Regulations 1995
 |id=Statutory Instrument 1995 No. 1804
 |publisher=[[legislation.gov.uk]]
 |year=1995
 |isbn=978-0-11-053334-6
 |access-date=27 August 2006
 |archive-date=17 October 2010
 |archive-url=https://web.archive.org/web/20101017003707/http://www.legislation.gov.uk/uksi/1995/1804/contents/made
 |url-status=live
}}</ref>

Immediately following the United Kingdom's [[Brexit|vote to withdraw from the European Union]], it was reported that some retailers requested to revert to imperial units, with some reverting without permission. A poll following the 2016 vote also found that 45% of Britons sought to revert to selling produce in imperial units.<ref>{{Cite news |first=Adam |last=Taylor |date=31 August 2016 |url=https://www.washingtonpost.com/news/worldviews/wp/2016/08/31/after-brexit-some-brits-want-to-ditch-the-metric-system-too/ |title=After Brexit, some Brits want to ditch the metric system, too |newspaper=[[The Washington Post]] |access-date=4 October 2016 |archive-date=5 October 2016 |archive-url=https://web.archive.org/web/20161005170845/https://www.washingtonpost.com/news/worldviews/wp/2016/08/31/after-brexit-some-brits-want-to-ditch-the-metric-system-too/ |url-status=live }}</ref>

The UK government started a consultation on 3 June 2022 on the choice of units of measurement markings.<ref>{{cite web |url=https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales |title=Choice on units of measurement: Markings and sales |work=gov.uk |access-date=20 October 2023 |date=3 June 2022 |archive-date=7 November 2023 |archive-url=https://web.archive.org/web/20231107040700/https://www.gov.uk/government/consultations/choice-on-units-of-measurement-markings-and-sales |url-status=live }}</ref>

Imperial units remain in common everyday use for human body measurements, in particular [[stone (unit)|stone]]s and [[pound (mass)|pound]]s for weight, and [[foot (unit)|feet]] and [[inch]]es for height.

Fuel economy is often advertised in miles per imperial gallon, which may lead to some confusion for users of US gallons for American manufactured cars.<ref>{{cite web |title=UK owners&nbsp;... MPG imperial or US gallons? |url=https://priuschat.com/threads/uk-owners-mpg-imperial-or-us-gallons.53300/ |access-date=2023-11-18 |website=PriusChat |archive-date=18 November 2023 |archive-url=https://web.archive.org/web/20231118181641/https://priuschat.com/threads/uk-owners-mpg-imperial-or-us-gallons.53300/ |url-status=live }}</ref>

Heating, air conditioning, and gas cooking appliances occasionally display power in British thermal units per hour (BTU/h).<ref>{{Cite web |title=Honeywell 9000 BTU Portable Air Conditioner - White - HT09CESAWK |url=https://www.airconcentre.co.uk/products/honeywell-9000-btu-3-in-1-portable-air-conditioner-ht09cesawk |access-date=2023-11-18 |website=Airconcentre.co.uk |archive-date=18 November 2023 |archive-url=https://web.archive.org/web/20231118181641/https://www.airconcentre.co.uk/products/honeywell-9000-btu-3-in-1-portable-air-conditioner-ht09cesawk |url-status=live }}</ref>

=== United States ===
{{See also|Metrication in the United States|}}

[[File:Measuring cup.jpg|thumb|A measuring cup, manufactured and sold in the United States (circa 1980), features graduations in both metric and US customary systems. Held in the right hand, a person would have the metric graduations in front, facing them; but they might hold it in their left hand, and read from the customary graduations.]]

Over time, the metric system has influenced the United States through international trade and standardisation. The use of the metric system was made legal as a system of measurement in 1866<ref>{{cite web|url=http://lamar.colostate.edu/~hillger/laws/metric-act.html |title=Metric Act of 1866 |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141010211054/http://lamar.colostate.edu/~hillger/laws/metric-act.html |archive-date=10 October 2014}}</ref> and the United States was a founding member of the [[International Bureau of Weights and Measures]] in 1875.<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/laws/metric-convention.html |title=Metric Convention of 1875 |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014 |url-status=dead |archive-url=https://web.archive.org/web/20050301093830/http://lamar.colostate.edu/~hillger/laws/metric-convention.html |archive-date=1 March 2005}}</ref> The system was officially adopted by the federal government in 1975 for use in the military and government agencies, and as preferred system for trade and commerce.<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/laws/metric-conv.html |archive-url=https://web.archive.org/web/20030714062847/http://lamar.colostate.edu/~hillger/laws/metric-conv.html |url-status=dead |archive-date=14 July 2003 |title=Metric Conversion Act of 1975 |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014}}</ref> Attempts in the 1990s to make it mandatory for federal and state road signage to use metric units failed and it remains voluntary.<ref>{{cite web|url=http://lamar.colostate.edu/~hillger/laws/natl-highway.html |archive-url=https://web.archive.org/web/20021214182707/http://lamar.colostate.edu/~hillger/laws/natl-highway.html |url-status=dead |archive-date=14 December 2002 |title=National Highway System Designation Act of 1995 |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014}}</ref>

A 1992 amendment to the [[Fair Packaging and Labeling Act|Fair Packaging and Labeling Act (FPLA)]], which took effect in 1994, required labels on federally regulated "consumer commodities"<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/laws/fpla.html#1459 |archive-url=https://web.archive.org/web/20021214183930/http://lamar.colostate.edu/~hillger/laws/fpla.html#1459 |url-status=dead |archive-date=14 December 2002 |title=Fair Packaging and Labeling Act |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014}}</ref> to include both [[SI|metric]] and [[US customary units]]. As of 2013, all but one US state ([[New York (state)|New York]]) have passed laws permitting metric-only labels for the products they regulate.<ref>{{cite web |url=http://lamar.colostate.edu/~hillger/#newyork |title=U.S. Metric Association (USMA) |website=USMA |publisher=U.S. Metric Association |access-date=24 November 2014|url-status=dead|archive-url=https://archive.today/20121220212344/http://lamar.colostate.edu/~hillger/#newyork|archive-date=20 December 2012}}</ref>

After many years of informal or optional metrication, the American public and much of the private business and industry still use US customary units today.<ref>{{cite web |url=https://www.motherjones.com/politics/1999/01/waits-and-measures/ |date=January 1999 |title=Waits and Measures |work=[[Mother Jones (magazine)|Mother Jones]] |first=Jason |last=Zengerle |access-date=24 November 2014 |archive-date=19 December 2014 |archive-url=https://web.archive.org/web/20141219194108/http://www.motherjones.com/politics/1999/01/waits-and-measures |url-status=live }}</ref> At least two states, Kentucky and California, have even moved towards demetrication of highway construction projects.<ref>{{cite web |title=Design Memorandum No. 11-98: English Conversion |date=4 November 1998 |access-date=20 October 2023 |website=transportation.ky.gov |url=http://transportation.ky.gov/design/memos/11-98.htm |archive-url=https://web.archive.org/web/20101124224700/http://transportation.ky.gov/design/memos/11-98.htm |archive-date=24 November 2010}}</ref><ref>{{cite web|url=http://www.dot.ca.gov/design/stp/memo/metric-to-english-transition.pdf|title=Metric to U.S. Customary Units (English) Transition|access-date=15 December 2017|publisher=Dot.ca.gov|archive-url=https://web.archive.org/web/20171216091109/http://www.dot.ca.gov/design/stp/memo/metric-to-english-transition.pdf|archive-date=16 December 2017|url-status=dead}}</ref><ref>{{cite book |url=http://www.dot.ca.gov/design/stp/memo/UOM-Metric_or_English.pdf |title=Declaration of Units of Measure—"Metric" or "English" Project |date=16 June 2006 |publisher=State of California, Department of Transportation |first=Richard D. |last=Land |access-date=15 December 2017 |archive-url=https://web.archive.org/web/20171216034812/http://www.dot.ca.gov/design/stp/memo/UOM-Metric_or_English.pdf |archive-date=16 December 2017 |url-status=dead}}</ref>

=== Canada ===
{{See also||Metrication in Canada}}
Canada legally allows for dual labelling of goods provided that the metric unit is listed first and that there is a distinction of whether a liquid measure is a US or a Canadian (imperial) unit.<ref name="CanadaDuellabel">{{cite book |url=http://www.inspection.gc.ca/english/fssa/labeti/guide/ch2e.shtml |title=Chapter 2 – Basic Labelling Requirements |access-date=16 May 2007 |publisher=Canadian Food Inspection Agency |pages=(also available in French) |archive-date=10 June 2007 |archive-url=https://web.archive.org/web/20070610025606/http://www.inspection.gc.ca/english/fssa/labeti/guide/ch2e.shtml |url-status=live }}</ref>

=== Belize ===
[[Belize]], which is a former British colony, uses both the metric and British imperial systems.<ref>{{Cite web | title=Archived copy | url=https://www.agm.gov.bz/uploads/laws/6397706ec2279_Cap_294_National_Metrology_Act.pdf | archive-url=https://web.archive.org/web/20241225163436/https://www.agm.gov.bz/uploads/laws/6397706ec2279_Cap_294_National_Metrology_Act.pdf | archive-date=2024-12-25}}</ref><ref name="Eltringham">{{cite book |last1=Eltringham |first1=Peter |title=The Rough Guide to Belize |date=2001 |publisher=Rough Guides |isbn=1858287103 |page=45}}</ref> [[Mile]]s are the most commonly used unit for measuring distance,<ref name="Lougheed">{{cite book |last1=Lougheed |first1=Vivien |title=Belize |date=2005 |publisher=Hunter Publishing |isbn=1588435083 |page=39}}</ref> and petrol is sold in [[US gallon]]s (similar to some countries in Latin America).

== Metrication mishaps ==
Confusion over units during the process of metrication can sometimes lead to accidents. In 1983, an [[Air Canada]] [[Boeing 767]], nicknamed the "[[Gimli Glider]]" following the incident, ran out of fuel in midflight.  The incident was caused, in a large part, by the confusion over the conversion between litres, kilograms, and pounds, resulting in the aircraft receiving {{convert|22,300|lb|kg|comma=gaps}} of fuel instead of the required {{convert|22,300|kg|comma=gaps}}.<ref>{{Cite book|author=Merran Williams |date=July–August 2003 |title=The 156-tonne GIMLI GLIDER |publisher=Flight Safety Australia |pages=22, 25 |url=http://www.casa.gov.au/fsa/2003/jul/22-27.pdf |access-date=5 November 2007 |url-status=dead |archive-url=https://web.archive.org/web/20071127211746/http://www.casa.gov.au/fsa/2003/jul/22-27.pdf
|archive-date=27 November 2007}}</ref>

While not strictly an example of national metrication, the use of two different measurement systems was a contributing factor in the loss of the [[Mars Climate Orbiter]] in 1999.  The [[National Aeronautics and Space Administration]] (NASA) specified metric units in the contract.  NASA and other organisations worked in metric units, but one subcontractor, [[Lockheed Martin]], provided thruster performance data to the team in [[pound force]]-seconds instead of [[newton (unit)|newton]]-seconds.  The spacecraft was intended to orbit [[Mars]] at about {{convert|150|km|mi}} in altitude, but the incorrect data meant that it descended to about {{convert|57|km|mi}}.  As a result, it burned up in the [[Atmosphere of Mars|Martian atmosphere]].<ref>{{cite web |title=NASA's metric confusion caused Mars orbiter loss |url=http://edition.cnn.com/TECH/space/9909/30/mars.metric/ |date=30 September 1999 |website=CNN |access-date=24 May 2013 |archive-date=18 January 2013 |archive-url=https://web.archive.org/web/20130118123539/http://edition.cnn.com/TECH/space/9909/30/mars.metric/ |url-status=dead }}</ref>

== See also ==
{{portal| mathematics | physics }}
{{div col|colwidth=18em}}
* [[History of the metric system]]
* [[Metre Convention]] 
* [[Metrication opposition]]
* [[Conversion of units]]
* [[Metric engine (American expression)]]
* [[Language reform]]
* [[Preferred numbers]]
* [[Spread of the Latin script]]
* [[Decimalisation]]
{{end div col}}
{{ clear }}

== References ==
{{reflist}}

{{Metrication|state=expanded}}
{{Systems of measurement}}
{{Authority control}}

[[Category:Metrication| ]]