View source for Calorie

{{short description|Unit of energy used in nutrition}}
{{Redirect|kcal|text=This article is about the unit of energy. For other uses, see [[KCAL (disambiguation)]] and [[Calorie (disambiguation)]].}}
{{Infobox unit
| name          = calorie
| image         = Energy drink and fast food cheeseburger calorie comparison.jpg
| caption       = A {{convert|24|USfloz|ml|adj=on}} [[Monster Energy|Monster]] [[energy drink]] (right) with 330 ''large'' calories
| quantity      = [[energy]]
| symbol        = cal
| units1        = [[SI unit]]s
| inunits1      = 4.184 [[Joule|J]]
}}
The '''calorie''' is a [[unit of energy]] that originated from the [[caloric theory]] of [[heat]].<ref name="morris1992" /><ref name="marsh2020" /> The '''large calorie''', '''food calorie''', '''dietary calorie''',  or '''kilogram calorie''' is defined as the amount of heat needed to raise the [[temperature]] of one [[liter]] of [[water]] by one degree [[Celsius]] (or one [[kelvin]]).<ref name="morris1992" /><ref name="Webster" /> The '''small calorie''' or '''gram calorie''' is defined as the amount of heat needed to cause the same increase in one [[milliliter]] of water.<ref name="Webster" /><ref name="Cambridge" /><ref name="Oxford" /><ref name="morris1992" /> Thus, 1 large calorie is equal to 1,000 small calories.

In [[nutrition]] and [[food science]], the term ''calorie'' and the symbol ''cal'' [[Calorie#Nutrition|may refer to the large unit or to the small unit in different regions of the world]]. It is generally used in publications and package labels to express the [[nutritional value|energy value]] of foods in per serving or per weight, recommended [[Dietary Reference Intake|dietary caloric intake]],<ref name=FDA2019/><ref name=NHS2019/> [[metabolic rate]]s, etc. Some authors recommend the spelling ''Calorie'' and the symbol ''Cal'' (both with a capital C) if the large calorie is meant, to avoid confusion;<ref name=conn2019/> however, this convention is often ignored.<ref name=FDA2019/><ref name=NHS2019/><ref name=conn2019/>

In [[physics]] and [[chemistry]], the word ''calorie'' and its symbol usually refer to the small unit, the large one being called ''kilocalorie'' (kcal). However, the kcal is not officially part of the [[International System of Units]] (SI), and is regarded as obsolete,<ref name=marsh2020/> having been replaced in many uses by the [[SI derived unit]] of [[energy]], the [[joule]] (J),<ref name=BIPM9th/> or the kilojoule (kJ) for 1000 joules.

The precise equivalence between calories and joules has varied over the years, but in [[thermochemistry]] and nutrition it is now generally assumed that one (small) calorie ('''thermochemical calorie''') is equal to exactly 4.184&nbsp;J, and therefore one kilocalorie (one large calorie) is 4184&nbsp;J or 4.184&nbsp;kJ.<ref name=BIPM7th/><ref name=FAO2003/>

==History==

The term "calorie" comes {{ety|la|calor|heat}}.<ref name="MW_calorie">{{cite encyclopedia |title="Calorie." |encyclopedia=Merriam-Webster.com Dictionary |url=https://www.merriam-webster.com/dictionary/calorie |access-date=2024-03-20 }}</ref> It was first introduced by [[Nicolas Clément]], as a unit of [[heat]] energy, in lectures on experimental [[calorimetry]] during the years 1819–1824. This was the "large" calorie.<ref name=marsh2020/><ref name=harg2007/><ref name=harg2006/> The term (written with lowercase "c") entered French and English dictionaries between 1841 and 1867.

The same term was used for the "small" unit by [[Pierre Antoine Favre]] (chemist) and Johann T. Silbermann (physicist) in 1852.

In 1879, [[Marcellin Berthelot]] distinguished between gram-calorie and kilogram-calorie, and proposed using "Calorie", with capital "C", for the large unit.<ref name=marsh2020/> This usage was adopted by [[Wilbur Olin Atwater]], a professor at [[Wesleyan University]], in 1887, in an influential article on the energy content of food.<ref name=marsh2020/><ref name=harg2007/>

The smaller unit was used by U.S. physician [[Joseph Howard Raymond]], in his classic 1894 textbook ''A Manual of Human Physiology''.<ref name=raym1894/> He proposed calling the "large" unit "kilocalorie", but the term did not catch on until some years later.

The small calorie (cal) was recognized as a unit of the [[CGS system]] in 1896,<ref name=marsh2020/><ref name=harg2006/> alongside the already-existing CGS unit of energy, the [[erg]] (first suggested by Clausius in 1864, under the name ''ergon'', and officially adopted in 1882).

In 1928, there were already serious complaints about the possible confusion arising from the two main definitions of the calorie and whether the notion of using the capital letter to distinguish them was sound.<ref name=marks1928/>

The joule was the officially adopted SI unit of energy at the ninth [[General Conference on Weights and Measures]] in 1948.<ref name=CIPM1948/><ref name=BIPM9th/> The calorie was mentioned in the 7th edition of the SI brochure as an example of a non-SI unit.<ref name=BIPM7th/>

The alternate spelling {{linktext|calory}} is a less-common, non-standard variant.<ref name="MW_calorie" />

==Definitions==
The "small" calorie is broadly defined as the amount of energy needed to increase the temperature of 1&nbsp;gram of water by 1&nbsp;°C (or 1&nbsp;K, which is the same increment, a gradation of one percent of the interval between the melting point and the boiling point of water).<ref name="Cambridge" /><ref name="Oxford" /> The actual amount of energy required to accomplish this temperature increase depends on the atmospheric pressure and the starting temperature; different choices of these parameters have resulted in several different precise definitions of the unit.

{|class=wikitable
|-
! Name !! Symbol !! Conversions !! Definition and notes
|- valign=top
| [[Thermochemistry|Thermochemical]] calorie || cal<sub>th</sub>
| ≡ {{val|4.184|ul=J}}
≈&nbsp;{{val|0.003964|ul=BTU}}
≈&nbsp;{{val|1.162|e=-6|ul=kW.h}}
≈&nbsp;{{val|2.611|e=19|ul=eV}}
| The amount of energy equal to exactly '''4.184&nbsp;J''' ([[joule]]s) and 1&nbsp;kJ ≈ 0.239&nbsp;kcal.<ref name="iso31-4" /><ref name=Rossini/><ref name=lynch1974/><ref name=FAO2003/>{{efn|name=thermochemical}}
|- valign=top
| 4&nbsp;°C calorie || cal<sub>4</sub>
| ≈ 4.204 J
≈&nbsp;<!-- {{convert|4.204|J|BTU|disp=output only}} -->{{val|0.003985|u=BTU}}
≈&nbsp;{{convert|4.204|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.204|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 3.5 to 4.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| 15&nbsp;°C calorie || cal<sub>15</sub>
| ≈ 4.1855 J
≈&nbsp;<!-- {{convert|4.1855|J|BTU|disp=output only}} -->{{val|0.0039671|u=BTU}}
≈&nbsp;{{convert|4.1855|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1855|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 14.5 to 15.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}} Experimental values of this calorie ranged from 4.1852 to 4.1858&nbsp;J. The [[CIPM]] in 1950 published a mean experimental value of 4.1855&nbsp;J, noting an uncertainty of 0.0005&nbsp;J.<ref name="iso31-4" />
|- valign=top
| 20&nbsp;°C calorie || cal<sub>20</sub>
| ≈ 4.182 J
≈&nbsp;<!-- {{convert|4.182|J|BTU|disp=output only}} -->{{val|0.003964|u=BTU}}
≈&nbsp;{{convert|4.182|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.182|J|eV|disp=output only}}
| The amount of energy required to warm one gram of air-free water from 19.5 to 20.5&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| Mean calorie || cal<sub>mean</sub>
| ≈ 4.190 J
≈&nbsp;<!-- {{convert|4.19|J|BTU|disp=output only}} -->{{val|0.003971|u=BTU}}
≈&nbsp;{{convert|4.190|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.190|J|eV|disp=output only}}
| Defined as {{frac|100}} of the amount of energy required to warm one gram of air-free water from 0 to 100&nbsp;°C at standard atmospheric pressure.{{efn|name=pressure}}
|- valign=top
| International [[steam table|Steam Table]] calorie (1929) ||
| ≈ 4.1860 J
≈&nbsp;<!-- {{convert|4.1868|J|BTU|disp=output only}} -->{{val|0.0039683|u=BTU}}
≈&nbsp;{{convert|4.1868|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1868|J|eV|disp=output only}}
| Defined as {{frac|860}} "international" watt hours = {{frac|180|43}} "international" joules exactly.{{efn|The figure depends on the conversion factor between "international joules" and "absolute" (modern, SI) joules. Using the mean international ohm and volt ({{val|1.00049|u=Ω}}, {{val|1.00034|u=V}}),<ref name=iupac/> the "international joule" is about {{val|1.00019|u=J}}, using the US international ohm and volt ({{val|1.000495|u=Ω}}, {{val|1.000330|u=V}}) it is about {{val|1.000165|u=J}}, giving {{val|4.18684}} and {{val|4.18674|u=J}}, respectively.}}
|- valign=top
| International Steam Table calorie (1956) || cal<sub>IT</sub>
| ≡ 4.1868 J
≈&nbsp;<!-- {{convert|4.1868|J|BTU|disp=output only}} -->{{val|0.0039683|u=BTU}}
<nowiki>=</nowiki>&nbsp;{{convert|4.1868|J|kW.h|disp=output only}}
≈&nbsp;{{convert|4.1868|J|eV|disp=output only}}
| Defined as 1.163&nbsp;mW⋅h = 4.1868&nbsp;J exactly. This definition was adopted by the Fifth International Conference on Properties of Steam (London, July 1956).<ref name="iso31-4" />
|}
{{notelist|refs=
{{efn|name=thermochemical|The 'Thermochemical calorie' was defined by Rossini simply as 4.1833 international joules in order to avoid the difficulties associated with uncertainties about the heat capacity of water.  It was later redefined as 4.1840 J exactly.{{refn|name=FAO1971}}}}
{{efn|name=pressure|The [[standard atmospheric pressure]] can be taken to be {{val|101.325|u=kPa}}.}}
}}
The two definitions most common in older literature appear to be the ''15&nbsp;°C calorie'' and the ''thermochemical calorie''. Until 1948, the latter was defined as 4.1833 international joules; the current standard of 4.184&nbsp;J was chosen to have the new thermochemical calorie represent the same quantity of energy as before.<ref name="Rossini" />
<!--
  The [[joule]] was adopted as equivalent to {{val|e=7|u=erg}} in 1889.
-->

==Usage==
===Nutrition===
In the [[United States]] and Canada, in a nutritional context, the "large" unit is used almost exclusively.<ref>{{Cite journal |last=Nutrition |first=Center for Food Safety and Applied |date=7 March 2022 |title=Changes to the Nutrition Facts Label |url=https://www.fda.gov/food/food-labeling-nutrition/changes-nutrition-facts-label |archive-url=https://web.archive.org/web/20190518044608/https://www.fda.gov/food/food-labeling-nutrition/changes-nutrition-facts-label |url-status=dead |archive-date=May 18, 2019 |journal=FDA |language=en}}</ref><ref>{{Cite web |last= |title=Elements within the Nutrition Facts table |url=https://inspection.canada.ca/en/food-labels/labelling/industry/nutrition-labelling/elements-within-nutrition-facts-table#s2c1 |url-status=live |archive-url=https://web.archive.org/web/20240625213453/https://inspection.canada.ca/en/food-labels/labelling/industry/nutrition-labelling/elements-within-nutrition-facts-table#s2c1 |archive-date=2024-06-25 |access-date=2025-04-23 |website=[[Canadian Food Inspection Agency]] |language=en }}</ref> It is generally written "calorie" with lowercase "c" and symbol "cal", even in government publications.<ref name=FDA2019/><ref name=NHS2019/> The SI unit [[kilojoule]] (kJ) may be used instead, in legal or scientific contexts.<ref name=ukmetric2012/><ref name=NPL2016/> Most American nutritionists prefer the unit kilocalorie to the unit kilojoules, whereas most physiologists prefer to use kilojoules. In the majority of other countries, nutritionists prefer the kilojoule to the kilocalorie.<ref name=patt2017/>

In the [[European Union]], on [[nutrition facts label]]s, energy is expressed in both kilojoules and kilocalories, abbreviated as "kJ" and "kcal" respectively.<ref>{{Cite web |title=EU Regulation No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers |url=https://eur-lex.europa.eu/eli/reg/2011/1169/oj#d1e2548-18-1 |access-date=18 April 2022 |website=EUR-Lex |language=en}}</ref>

In [[China]], only kilojoules are given.<ref>{{Cite web |last=USDA |date=2013 |title=China, General Rules for Nutrition Labeling of Prepackaged Foods |url=https://apps.fas.usda.gov/newgainapi/api/report/downloadreportbyfilename?filename=General%20Rules%20for%20Nutrition%20Labeling%20of%20Prepackaged%20Foods%20_Beijing_China%20-%20Peoples%20Republic%20of_1-9-2013.pdf |access-date=18 April 2022}}</ref>

===Food energy===
The unit is most commonly used to express [[food energy]], namely the [[specific energy]] (energy per mass) of metabolizing different types of food.  For example, [[fat]] (triglyceride lipids) contains 9&nbsp;kilocalories per gram (kcal/g), while [[carbohydrate]]s (sugar and starch) and [[protein (nutrient)|protein]] contain approximately 4&nbsp;kcal/g.<ref name=SciAm/> Alcohol in food contains 7&nbsp;kcal/g.<ref>{{Cite web|url=http://www.nutristrategy.com/nutrition/calories.htm|title=Calories - Fat, Protein, Carbohydrates, Alcohol. Calories per gram|website=Nutristrategy }}</ref> The "large" unit is also used to express recommended nutritional intake or consumption, as in "calories per day".

[[Dieting]] is the practice of [[eating]] food in a regulated way to decrease, maintain, or increase [[body weight]], or to prevent and treat diseases such as [[diabetes]] and [[obesity]]. As weight loss depends on reducing caloric intake, [[List of diets|different kinds]] of [[Calorie restriction|calorie-reduced]] diets have been shown to be generally effective.<ref name="Strychar">{{Cite journal |last=Strychar |first=I. |date=3 January 2006 |title=Diet in the management of weight loss |journal=Canadian Medical Association Journal |volume=174 |issue=1 |pages=56–63 |doi=10.1503/cmaj.045037 |issn=0820-3946 |pmc=1319349 |pmid=16389240}}</ref>

===Chemistry and physics===
In other scientific contexts, the term "calorie" and the symbol "cal" almost always refers to the small unit; the "large" unit being generally called "kilocalorie" with symbol "kcal". It is mostly used to express the amount of energy released in a [[chemical reaction]] or [[Phase transition|phase change]], typically per [[mole (unit)|mole]] of substance, as in [[kilocalorie per mole|kilocalories per mole]].<ref name=rappo2007/> It is also occasionally used to specify other energy quantities that relate to reaction energy, such as [[bond energy|enthalpy of formation]] and the size of [[activation energy|activation barrier]]s.<ref name=bhag2002/> However, it is increasingly being superseded by the SI unit, the joule (J); and metric multiples thereof, such as the kilojoule (kJ).{{citation needed|date=March 2023}}

The lingering use in chemistry is largely because the energy released by a reaction in [[aqueous solution]], expressed in kilocalories per mole of reagent, is numerically close to the concentration of the reagent in moles per [[liter]] multiplied by the change in the temperature of the solution in kelvins or degrees Celsius. However, this estimate assumes that the [[volumetric heat capacity]] of the solution is 1&nbsp;kcal/([[litre|L]]⋅[[kelvin|K]]), which is not exact even for pure water.{{citation needed|date=March 2023}}

==See also==
{{portal|Energy|Food|Science}}
{{div col|colwidth=30em}}
* [[Basal metabolic rate]]
* [[Caloric theory]]
* [[Conversion of units of energy]]
* [[Empty calorie]]
* [[Food energy]]
* [[A calorie is a calorie]]
* [[Nutrition facts label]]
* [[British thermal unit]]
* [[Satiety value]]
* [[Caloric deficit]]{{div col end}}

==References==
{{reflist|30em|refs=

<ref name="Rossini">{{Cite journal |last=Rossini |first=Fredrick |author-link=Frederick Rossini |year=1964 |title=Excursion in Chemical Thermodynamics, from the Past into the Future |url=http://iupac.org/publications/pac/8/2/0095/ |journal=Pure and Applied Chemistry |volume=8 |issue=2 |page=107 |doi=10.1351/pac196408020095 |access-date=21 January 2013 |quote=both the IT calorie and the thermochemical calorie are completely independent of the heat capacity of water. |doi-access=free|url-access=subscription }}</ref>

<ref name="Webster">{{Cite web |date=1 August 2017 |title=Definition of Calorie |url=https://www.merriam-webster.com/dictionary/calorie |access-date=4 September 2017 |website=Merriam-Webster}}</ref>

<ref name="iupac">{{Cite book |last=International Union of Pure and Applied Chemistry (IUPAC) |url=https://archive.org/details/compendiumofanal0000unse |title=Compendium of Analytical Nomenclature |year=1997 |isbn=0-86542-615-5 |edition=3 |chapter=1.6 Conversion tables for units |publisher=Institut d'Estudis Catalans |author-link=International Union of Pure and Applied Chemistry |access-date=31 August 2013 |chapter-url=http://iupac.org/publications/analytical_compendium/Cha01sec6.pdf |archive-url=https://web.archive.org/web/20031016030854/http://www.iupac.org/publications/analytical_compendium/Cha01sec6.pdf |archive-date=2003-10-16 |url-status=live |url-access=registration}}</ref>

<ref name="rappo2007">Zvi Rappoport ed. (2007), [https://books.google.com/books?id=4PdYwo25VP8C&pg=PA12 "The Chemistry of Peroxides"], Volume 2 page 12.</ref>

{{refn|name=FAO1971|{{Cite web |last=FAO |author-link=FAO |year=1971 |title=The adoption of joules as units of energy |url=http://www.fao.org/docrep/meeting/009/ae906e/ae906e17.htm}}}}

<ref name="FAO2003">United Nations Food and Agriculture Organization (2003): "[http://www.fao.org/docrep/006/Y5022E/y5022e04.htm FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors] {{Webarchive|url=https://web.archive.org/web/20100524003622/http://www.fao.org/DOCREP/006/Y5022E/y5022e04.htm |date=2010-05-24 }}". Accessed on 21 January 2022.</ref>

<ref name="harg2006">JL Hargrove, "history of the calorie in nutrition", ''J Nutr'' 136/12 (December 2006), pp. 2957–2961.</ref>

<ref name="harg2007">{{Cite journal |last=Hargrove |first=James L |year=2007 |title=Does the history of food energy units suggest a solution to "Calorie confusion"? |journal=Nutrition Journal |volume=6 |issue=44 |pages=44 |doi=10.1186/1475-2891-6-44 |pmc=2238749 |pmid=18086303 |doi-access=free }}</ref>

<ref name="iso31-4">International Standard [[ISO 31-4]]: Quantities and units, Part 4: Heat. Annex B (informative): Other units given for information, especially regarding the conversion factor. [[International Organization for Standardization]], 1992.</ref>

<ref name="SciAm">{{Cite news |title=How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods? |language=en |work=Scientific American |url=https://www.scientificamerican.com/article/how-do-food-manufacturers/ |access-date=8 September 2017}}</ref>

<ref name="CIPM1948">"[https://www.bipm.org/en/committees/cg/cgpm/9-1948/resolution-3  Resolution 3 of the 9th CGPM (1948):  Triple point of water; thermodynamic scale with a single fixed point; unit of quantity of heat (joule)]", BIPM. {{Webarchive|url=https://web.archive.org/web/20210614063830/https://www.bipm.org/en/committees/cg/cgpm/9-1948/resolution-3 |date=2021-06-14 }}.</ref>

<ref name="BIPM9th">Bureau International des Poids et Mesures (2019): ''[https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.10 The International System of Units (SI)] {{Webarchive|url=https://web.archive.org/web/20220120160044/https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.10 |date=2022-01-20 }}'', 9th edition.</ref>

<ref name="BIPM7th">Bureau International des Poids et Mesures  (1998): ''[https://www.bipm.org/documents/20126/41483022/si_brochure_7.pdf/36560ee5-8292-a297-ffe6-cbdf729c22a6?version=1.5 The International System of Units (SI)] {{Webarchive|url=https://web.archive.org/web/20220120160044/https://www.bipm.org/documents/20126/41483022/si_brochure_7.pdf/36560ee5-8292-a297-ffe6-cbdf729c22a6?version=1.5 |date=2022-01-20 }}'', 7th edition.</ref>

<ref name="FDA2019">U. S. Food and Drug Administration (2019): "[https://www.fda.gov/food/nutrition-education-resources-materials/calories-menu Calories on the Menu - Information for ] {{Webarchive|url=https://web.archive.org/web/20220120213703/http://www.fda.gov/food/nutrition-education-resources-materials/calories-menu |date=2022-01-20 }}". Online document at the [https://www.fda.gov FDA Website] {{Webarchive|url=https://web.archive.org/web/20130915112715/https://www.fda.gov/ |date=2013-09-15 }}, dated 5 August 2019. Accessed on 2022-01-20.</ref>

<ref name="NHS2019">U. K. National Health Service (2019): "[https://www.nhs.uk/common-health-questions/food-and-diet/what-should-my-daily-intake-of-calories-be/ What should my daily intake of calories be?] {{Webarchive|url=https://web.archive.org/web/20220121092208/https://www.nhs.uk/common-health-questions/food-and-diet/what-should-my-daily-intake-of-calories-be/ |date=2022-01-21 }}". Online document at the [https://www.nhs.uk/ NHS website] {{Webarchive|url=https://web.archive.org/web/20200502074502/http://www.wales.nhs.uk/ |date=2020-05-02 }}, dated 24 October 2019. Accessed on 2022-01-20.</ref>

<ref name="conn2019">{{Cite web |last1=Conn |first1=Carole |last2=Len Kravitz |title=Remarkable Calorie |url=http://www.unm.edu/~lkravitz/Article%20folder/remarkablecalorie.html |access-date=1 March 2019 |publisher=University of New Mexico}}</ref>

<ref name="bhag2002">{{Cite book |last=Bhagavan |first=N. V. |url=https://books.google.com/books?id=b7Dc9bOs9uAC&q=calorie+%22activation+barrier%22&pg=PA76 |title=Medical Biochemistry |date=2002 |publisher=Academic Press |isbn=9780120954407 |pages=76–77 |language=en |access-date=5 September 2017}}</ref>

<ref name="marks1928">{{Cite journal |last=Marks |first=Percy L. |date=14 January 1928 |title=The Two Calories, Percy L. Marks |journal=Nature |volume=121 |issue=3037 |pages=58 |doi=10.1038/121058d0 |doi-access=free |s2cid=4068300}}</ref>

<ref name="ukmetric2012">{{Cite web |date=24 February 2012 |title=Prospects improve for food energy labelling using SI units |url=http://metricviews.uk/2012/02/prospects-improve-for-food-energy-labelling-using-si-units/ |access-date=17 April 2013 |website=Metric Views |publisher=[[UK Metric Association]]}}</ref>

<ref name="NPL2016">{{Cite web |title=SI Conventions |url=http://www.npl.co.uk/reference/measurement-units/si-conventions/ |access-date=8 February 2016 |publisher=[[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]}}</ref>

<ref name="Cambridge">{{Cite web |title=Cambridge Dictionary: calorie |url=https://dictionary.cambridge.org/us/dictionary/english/calorie |access-date=9 November 2019}}</ref>

<ref name="lynch1974">{{Cite book |last=Lynch |first=Charles T. |url=https://books.google.com/books?id=QdU-lRMjOsgC&pg=PA444 |title=Handbook of Materials Science: General Properties, Volume 1 |date=1974 |publisher=CRC Press |isbn=9780878192342 |page=438 |access-date=8 March 2014}}</ref>

<ref name="patt2017">{{Cite book |last1=Kevin T. Patton |url=https://books.google.com/books?id=JtDwDQAAQBAJ&pg=PA537 |title=The Human Body in Health & Disease - E-Book |last2=Gary A. Thibodeau |date=11 January 2017 |publisher=Elsevier Health Sciences |isbn=978-0-323-40206-4 |page=537}}</ref>

<ref name="Oxford">{{Cite web |title=Definition of calorie noun from the Oxford Advanced American Dictionary |url=https://www.oxfordlearnersdictionaries.com/us/definition/american_english/calorie |access-date=9 November 2019}}</ref>

<ref name="marsh2020">Allison Marsh (2020): "[https://spectrum.ieee.org/how-counting-calories-became-a-science How Counting Calories Became a Science: Calorimeters defined the nutritional value of food and the output of steam generators] {{Webarchive|url=https://web.archive.org/web/20220121000718/https://spectrum.ieee.org/how-counting-calories-became-a-science |date=2022-01-21 }}"  Online article on the [https://spectrum.ieee.org IEEE Spectrum] {{Webarchive|url=https://web.archive.org/web/20220120232140/https://spectrum.ieee.org/ |date=2022-01-20 }} website, dated 29 December 2020. Accessed on 2022-01-20.</ref>

<ref name="raym1894">Joseph Howard Raymond (1894): ''[https://books.google.com/books?id=iG0CAAAAYAAJ&pg=PA166 A Manual of Human Physiology: Prepared with Special Reference to Students of Medicine] {{Webarchive|url=https://web.archive.org/web/20220121002825/https://books.google.com.br/books?id=iG0CAAAAYAAJ&pg=PA166 |date=2022-01-21 }}''. W.B. Saunders, 376 pages.</ref>

<ref name="morris1992">Christopher W. Morris (1992) ''Academic Press Dictionary of Science and Technology''. 2432 pages. {{isbn|9780122004001}}</ref>

}}

[[Category:Units of energy]]
[[Category:Heat transfer]]
[[Category:Non-SI metric units]]