Gauss (unit)

2025-09-05T23:30:20Z

2001:9E8:6A86:3800:3C8:AE32:F4D4:F3CA:

{{Short description|Unit of magnetic induction}}
{{Infobox unit
| name = gauss
| image =
| caption =
| standard = [[Gaussian units|Gaussian]] and [[Centimetre–gram–second_system_of_units#Electromagnetic_units_.28EMU.29|emu-cgs]]
| quantity = [[magnetic flux]] density (also known as [[Magnetic_field#The_B-field|magnetic induction]], or the {{math|'''B'''}}-field, or magnetic field)
| symbol = G ''or'' Gs
| symbol2 =
| namedafter = [[Carl Friedrich Gauss]]
| extralabel =
| extradata =
| units1 = [[SI derived units]]
| inunits1 = {{val|e=-4|u=tesla}}{{efn|The electromagnetic Gaussian and SI quantities ''correspond'' (symbol '≘') rather than being ''equal'' (symbol '{{=}}').}}
| units2 = Gaussian base units
| inunits2 = 1 cm−1/2⋅g1/2⋅s−1
| units3 = [[Centimetre–gram–second system of units#Electrostatic units (ESU)|esu-cgs]]
| inunits3 = 1/{{math|''c''}}{{sub|cgs}} esu{{efn|{{math|''c''}}{{sub|cgs}} {{=}} {{val|2.99792458e10}} is the numeric part of the [[speed of light]] when expressed in cgs units.}}
}}
[[File:Bendixen_-_Carl_Friedrich_Gauß,_1828.jpg | thumb | right | Carl Friedrich Gauß in 1828, aged 50 years old]]
The '''gauss''' (symbol: '''{{val|u=G}}''', sometimes '''Gs''') is a unit of measurement of magnetic induction, also known as [[magnetic flux density]]. The unit is part of the [[Gaussian units|Gaussian system]] of units, which inherited it from the older [[centimetre–gram–second system of units#Electromagnetic units .28EMU.29|centimetre–gram–second electromagnetic units]] (CGS-EMU) system. It was named after the German mathematician and physicist [[Carl Friedrich Gauss]] in 1936. One gauss is defined as one [[maxwell (unit)|maxwell]] per square [[centimetre]].

As the [[centimetre–gram–second system of units]] (cgs system) has been superseded by the [[International System of Units]] (SI), the use of the gauss has been deprecated by the standards bodies, but is still regularly used in various subfields of science, and preferred in [[astrophysics]].<ref>J. B. Zirker, ''The Magnetic Universe.'', Johns Hopkins University Press, Baltimore, 2009, p. 281.</ref> The SI unit for magnetic flux density is the [[Tesla (unit)|tesla]] (symbol T),<ref>''NIST Special Publication 1038'', Section 4.3.1</ref> which corresponds to {{gaps|10,000|gauss}}.

==Name, symbol, and metric prefixes==
Although not a component of the International System of Units, the usage of the gauss generally follows the rules for SI units. Since the name is derived from a person's name, its symbol is the uppercase letter "G". When the unit is spelled out, it is written in lowercase ("gauss"), unless it begins a sentence.<ref name="SIBrochure9thEd">{{SIbrochure9th}}</ref>{{rp|147–148}} The gauss may be combined with [[metric prefix]]es,<ref name="SIBrochure8th">{{SIbrochure8th}}</ref>{{rp|128}} such as in milligauss, mG (or mGs), or kilogauss, kG (or kGs).

==Unit conversions==
<math display="block">\begin{align}
1\,{\rm G} &= {\rm Mx}{\cdot}{\rm cm}^{-2} = \frac{\rm g}{{\rm Bi}{\cdot}{\rm s}^2}\\
&\text{ ≘ } 10^{-4}\,{\rm T} = 10^{-4}\frac{\rm kg}{{\rm A}{\cdot}{\rm s^2}}
\end{align}</math>

The gauss is the unit of magnetic flux density '''B''' in the system of [[Gaussian units]] and is equal to [[Maxwell (unit)|Mx]]/cm2 or [[gram (unit)|g]]/[[Abampere|Bi]]/s2, while the [[oersted]] is the unit of [[Magnetic_field#The_H-field|{{math|'''H'''}}-field]]. One [[tesla (unit)|tesla]] (T) corresponds to 104 gauss, and one [[ampere]] (A) per metre corresponds to 4π × 10−3 [[oersted]].


The units for [[magnetic flux]] Φ, which is the [[integral]] of [[Magnetic_field#The_B-field|magnetic {{math|'''B'''}}-field]] over an [[area]], are the [[weber (unit)|weber]] (Wb) in the [[SI]] and the [[Maxwell (unit)|maxwell]] (Mx) in the CGS-Gaussian system. The conversion factor is {{val|e=8|u=maxwell per weber}}, since [[flux]] is the integral of field over an area, area having the units of the square of distance, thus {{val|e=4|u=G/T}} (magnetic field conversion factor) times the square of {{val|e=2|u=cm/m}} (linear distance conversion factor). 108 Mx/Wb = 104 G/T × (102 cm/m)2.

==Typical values==
{{main|Orders of magnitude (magnetic field)}}
* 10−9–10−8 G – the magnetic field of the human brain
* 10−6–10−3 G – the magnetic field of Galactic [[molecular clouds]]. Typical magnetic field strengths within the interstellar medium of the [[Milky Way]] are ~5 μG.
* 0.25–0.60 G – the [[Earth's magnetic field]] at its surface
* 4 G – near [[Jupiter]]'s equator
* 25 G – the Earth's magnetic field in its [[Earth's outer core|core]]<ref name="buff2010">Buffett, Bruce A. (2010), "Tidal dissipation and the strength of the Earth's internal magnetic field", ''Nature'', volume 468, pages 952–954, {{doi|10.1038/nature09643}}</ref>
* 50 G – a typical [[refrigerator magnet]]
* 100 G – an [[iron]] [[magnet]]
* 1500 G – within a [[sun spot]]<ref>{{Cite web |url=http://www.coolmagnetman.com/magflux.htm |title=How strong are magnets?|last=Hoadley |first=Rick |website=www.coolmagnetman.com |access-date=2017-01-26 }}</ref>
* 10000 to 13000 G – [[remanence]] of a [[neodymium magnet|neodymium-iron-boron (NIB) magnet]]<ref>{{cite book |url=https://books.google.com/books?id=_y3LSh1XTJYC&pg=PT232 |page=232 |title=Design of Rotating Electrical Machines |first1=Juha |last1=Pyrhönen |first2=Tapani |last2=Jokinen |first3=Valéria |last3=Hrabovcová |publisher=John Wiley and Sons |year=2009 |isbn=978-0-470-69516-6 }}</ref>
* 16000 to 22000 G – [[saturation (magnetic)|saturation]] of high permeability iron alloys used in transformers<ref>{{cite book |editor1-last=Laughton |editor1-first=Michael A. |editor2-last=Warne |editor2-first=Douglas F. |title=Electrical Engineer's Reference Book |edition=Sixteenth |publisher=Newnes |year=2003 |isbn=0-7506-4637-3 |chapter=8 }}</ref>
* 3000–70000 G – a medical [[magnetic resonance imaging|magnetic resonance imaging machine]]
* 1012–1013 G – the surface of a [[neutron star]]<ref>{{cite web |title=How strong are magnets? |work=Experiments with magnets and our surroundings |publisher=Magcraft |url=http://www.coolmagnetman.com/magflux.htm |access-date=2007-12-14 }}</ref>
* 4 × 1013 G – the [[Schwinger limit]]
* 1014 G – the magnetic field of [[SGR J1745-2900]], orbiting the supermassive black hole [[Sagittarius A*|Sgr A*]] in the center of the Milky Way.
* 1015 G – the magnetic field of some newly created [[magnetar]]s<ref name="sciam_article">{{cite web
|date = March 2003
|first = Robert C.
|last = Duncan
|url = http://solomon.as.utexas.edu/~duncan/magnetar.html#Epilog
|title = Magnetars, Soft Gamma Repeaters and Very Strong Magnetic Fields
|publisher = University of Texas at Austin
|access-date = 2007-05-23
|url-status = dead
|archive-url = https://web.archive.org/web/20070611144512/http://solomon.as.utexas.edu/~duncan/magnetar.html#Epilog
|archive-date = 2007-06-11
}}</ref>
* 1017 G – the upper limit to neutron star magnetism<ref name="sciam_article" />

==See also==
*[[Tesla (unit)]]
*[[Centimetre–gram–second system of units]]
*[[Gaussian units]]

== Notes ==
{{notelist}}

==References==
{{reflist}}

{{CGS units}}

[[Category:Centimetre–gram–second system of units]]
[[Category:Units of magnetic flux density]]
[[Category:Carl Friedrich Gauss|Unit]]

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Gauss (unit)