View source for Fahrenheit

{{Short description|Temperature scale}}
{{Other uses}}
{{pp-pc|small=yes}}
{{Use American English|date=July 2019}}
{{Use dmy dates|date=May 2021}}
{{Infobox unit
| name          =  Fahrenheit
| image         = Raumthermometer Fahrenheit+Celsius.jpg
| caption       = Thermometer with Fahrenheit (marked on outer bezel) and [[Celsius]] (marked on inner dial) degree units.
| standard      = [[Imperial and US customary measurement systems|Imperial/US customary]]
| quantity      = Temperature
| symbol        = °F
| namedafter    = [[Daniel Gabriel Fahrenheit]]
| convertfromx  = yes
| units1        = [[SI base units]]
| inunits1      = {{sfrac|5|9}}({{math|''x''}}&nbsp;+459.67)&nbsp;[[Kelvin|K]]
| units2        = [[SI derived units]]
| inunits2      = {{sfrac|5|9}}({{math|''x''}}&nbsp;− 32)&nbsp;[[°C]]
| units3        = [[Imperial units|Imperial]]/[[US customary units|US]] [[absolute scale]]
| inunits3      = {{math|''x''}}&nbsp;+ 459.67&nbsp;[[Rankine scale|°Ra]]
}}
The '''Fahrenheit scale''' ({{IPAc-en|ˈ|f|æ|ɹ|ə|n|h|aɪ|t|,_|ˈ|f|ɑ:|ɹ|-}}) is a [[scale of temperature|temperature scale]] based on one proposed in 1724 by the European physicist [[Daniel Gabriel Fahrenheit]] (1686–1736).<ref>{{cite book |url=https://books.google.com/books?id=VC-RuN6moREC&q=fahrenheit%20temperature%20scale%20inventor%20book&pg=PA9 |page = 9 |first = Robert T. |last = Balmer |title = Modern Engineering Thermodynamics |publisher = Academic Press |year = 2010 |access-date = 17 July 2011 |isbn = 978-0-12-374996-3 }}</ref> It uses the '''degree Fahrenheit''' (symbol: '''°F''') as the unit. Several accounts of how he originally defined his scale exist, but the original paper suggests the lower defining point, 0&nbsp;°F, was established as the freezing [[temperature]] of a solution of [[brine]] made from a mixture of water, [[ice]], and [[ammonium chloride]] (a [[Salt (chemistry)|salt]]).<ref name=":0" /><ref>{{cite web |access-date = 2018-02-09 |title=Fahrenheit: Facts, History & Conversion Formulas |url=https://www.livescience.com/39916-fahrenheit.html |website = Live Science }}</ref> The other limit established was his best estimate of the average [[human body temperature]], originally set at 90&nbsp;°F, then 96&nbsp;°F (about 2.6&nbsp;°F less than the modern value due to a later redefinition of the scale).<ref name=":0">{{cite encyclopedia |url=https://www.britannica.com/science/Fahrenheit-temperature-scale |title = Fahrenheit temperature scale |encyclopedia = Encyclopædia Britannica Online |access-date = 25 September 2015 }}</ref>
For much of the 20th century, the Fahrenheit scale was defined by two fixed points with a 180&nbsp;°F separation: the temperature at which pure water freezes was defined as 32&nbsp;°F and the boiling point of water was defined to be 212&nbsp;°F, both at [[sea level]] and under [[standard atmospheric pressure]]. It is now formally defined using the [[Kelvin]] scale.<ref>{{cite web |url=https://www.nist.gov/blogs/taking-measure/busting-myths-about-metric-system |title = Busting Myths about the Metric System |publisher = US National Institute of Standards and Technology (NIST)|date = 6 October 2020|last1 = Benham |first1 = Elizabeth }}</ref><ref>{{cite book|title=NIST Handbook 44 -Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices - 2022|url=https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-44-current-edition |chapter-url=https://www.nist.gov/system/files/documents/2021/11/30/2022-HB44-Section-Appendix-C.pdf |archive-url=https://web.archive.org/web/20211227073804/https://www.nist.gov/system/files/documents/2021/11/30/2022-HB44-Section-Appendix-C.pdf |archive-date=2021-12-27 |url-status=live |chapter= Appendix C – General Tables of Units of Measurement |publisher = US National Institute of Standards and Technology (NIST)| date=29 November 2021 }}</ref>
It continues to be used in the United States (including its [[Unincorporated territories of the United States|unincorporated territories]]), its [[Compact of Free Association|freely associated states]] in the Western Pacific ([[Palau]], the [[Federated States of Micronesia]] and the [[Marshall Islands]]), the [[Cayman Islands]], and [[Liberia]].
Fahrenheit is commonly still used alongside the [[Celsius]] scale in other countries that use the U.S. [[metrological]] service, such as [[Antigua and Barbuda]], [[Saint Kitts and Nevis]], the [[The Bahamas|Bahamas]], and [[Belize]]. A handful of [[British Overseas Territories]], including the [[British Virgin Islands|Virgin Islands]], [[Montserrat]], [[Anguilla]], and Bermuda, also still use both scales.<ref>{{cite web |url=http://metricviews.org.uk/2012/10/50-years-of-celsius-weather-forecasts-%E2%80%93-time-to-kill-off-fahrenheit-for-good/ |title = 50 years of Celsius weather forecasts – time to kill off Fahrenheit for good? &#124; Metric Views |access-date = 28 July 2019 |archive-date = 2 October 2020 |archive-url=https://web.archive.org/web/20201002102817/http://metricviews.org.uk/2012/10/50-years-of-celsius-weather-forecasts-%E2%80%93-time-to-kill-off-fahrenheit-for-good/ |url-status = dead }}</ref> All other countries now use [[Celsius]] ("centigrade" until 1948), which was invented 18 years after the Fahrenheit scale.<ref>Celsius, Anders (1742) "Observationer om twänne beständiga grader på en thermometer" (Observations about two stable degrees on a thermometer), Kungliga Svenska Vetenskapsakademiens Handlingar (Proceedings of the Royal Swedish Academy of Sciences), 3: 171–180 and Fig. 1.</ref>
== Definition and conversion ==
{{temperature}}
Historically, on the Fahrenheit scale the [[freezing point]] of water was 32&nbsp;°F, and the [[boiling point]] was 212&nbsp;°F (at [[standard atmospheric pressure]]). This put the boiling and freezing points of water 180&nbsp;degrees apart.<ref name="rank" /> Therefore, a degree on the Fahrenheit scale was {{frac|1|180}} of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water were originally defined to be 100&nbsp;degrees apart. A temperature interval of 1&nbsp;°F was equal to an interval of {{frac|5|9}}&nbsp;degrees Celsius. With the Fahrenheit and Celsius scales now both defined by the [[kelvin]], this relationship was preserved, a temperature interval of 1&nbsp;°F being equal to an interval of {{frac|5|9}}&nbsp;K and of {{frac|5|9}}&nbsp;°C. The Fahrenheit and Celsius scales intersect numerically at −40 in the respective unit (i.e., −40&nbsp;°F ≘ −40&nbsp;°C).
[[Absolute zero]] is 0 K, −273.15&nbsp;°C, or −459.67&nbsp;°F. The [[Rankine Scale|Rankine temperature scale]] uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0&nbsp;°R{{snd}} the same way that the [[Kelvin]] temperature scale matches the Celsius scale, except that absolute zero is 0&nbsp;K.<ref name="rank">{{cite book |pages = 273–274 |first = Walt |last = Boyes |url=https://books.google.com/books?id=ZvscLzOlkNgC&q=rankine%20temperature%20scale%20book&pg=PA273 |title = Instrumentation Reference Book |publisher = Butterworth-Heinemann |year = 2009 |access-date = 17 July 2011 |isbn = 978-0-7506-8308-1 }}</ref>
The combination of [[degree symbol]] (°) followed by an uppercase letter F is the conventional symbol for the Fahrenheit temperature scale. A number followed by this symbol (and separated from it with a space) denotes a specific temperature point (e.g., "[[Gallium]] melts at 85.5763&nbsp;°F"). A difference between temperatures or an uncertainty in temperature is also conventionally written the same way as well, e.g., "The output of the heat exchanger experiences an increase of 72&nbsp;°F" or "Our standard uncertainty is ±5&nbsp;°F". However, some authors instead use the notation "An increase of {{not a typo|50&nbsp;F°}}" (reversing the symbol order) to indicate temperature differences. Similar conventions exist for the Celsius scale, see {{section link|Celsius#Temperatures_and_intervals}}.<ref>{{cite book |last1=Dingman |first1=S. L. |title=Fluvial Hydraulics |date=26 February 2009 |publisher=Oxford University Press, USA |isbn=978-0-19-517286-7 |page=522 |url=https://books.google.com/books?id=cvwRDAAAQBAJ&pg=PA522 |language=en}}</ref><ref>{{cite book |last1=Sogin |first1=Harold H. |last2=Hassan |first2=Kamal-Eldin |title=A design manual for regenerative heat exchangers of the rotary type |date=June 1956 |publisher=Wright Air Development Center |page=xii |url=https://books.google.com/books?id=6cYnAAAAMAAJ&pg=RA9-PR12 |language=en}}</ref>
=== Conversion (specific temperature point) ===
For an exact conversion between degrees Fahrenheit and Celsius, and kelvins of ''a specific temperature point'', the following formulas can be applied. Here, {{math|''f''}} is the value in degrees Fahrenheit, {{math|''c''}} the value in degrees Celsius, and {{math|''k''}} the value in kelvins:
* {{math|''f''}}&nbsp;°F to {{math|''c''}}&nbsp;°C: {{math|''c''}} = {{sfrac|{{math|''f''}} − 32|1.8}}
* {{math|''c''}}&nbsp;°C to {{math|''f''}}&nbsp;°F: {{math|''f''}} = {{math|''c''}} × 1.8 + 32
* {{math|''f''}}&nbsp;°F to {{math|''k''}}&nbsp;K: {{math|''k''}} = {{sfrac|{{math|''f''}} + 459.67|1.8}}
* {{math|''k''}}&nbsp;K to {{math|''f''}}&nbsp;°F: {{math|''f''}} = {{math|''k''}} × 1.8 − 459.67
There is also an exact conversion between Celsius and Fahrenheit scales making use of the correspondence −40&nbsp;°F ≘ −40&nbsp;°C. Again, {{math|''f''}} is the numeric value in degrees Fahrenheit, and {{math|''c''}} the numeric value in degrees Celsius:
* {{math|''f''}}&nbsp;°F to {{math|''c''}}&nbsp;°C: {{math|''c''}} = {{sfrac|{{math|''f''}} + 40|1.8}} − 40
* {{math|''c''}}&nbsp;°C to {{math|''f''}}&nbsp;°F: {{math|''f''}} = ({{math|''c''}} + 40) × 1.8 − 40
=== Conversion (temperature difference or interval) ===
When converting a ''temperature interval'' between the Fahrenheit and Celsius scales, only the ratio is used, without any constant (in this case, the interval has the same numeric value in kelvins as in degrees Celsius):
* {{math|''f''}}&nbsp;°F to {{math|''c''}}&nbsp;°C or {{math|''k''}}&nbsp;K: {{math|''c''}} = {{math|''k''}} = {{sfrac|{{math|''f''}}|1.8}}
* {{math|''c''}}&nbsp;°C or {{math|''k''}}&nbsp;K to {{math|''f''}}&nbsp;°F: {{math|''f''}} = {{math|''c''}} × 1.8 = {{math|''k''}} × 1.8
== History ==
Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale (which is not the final Fahrenheit scale), the zero point was determined by placing the [[thermometer]] in "a mixture of [[ice]], water, and ''salis Armoniaci''{{NoteTag|1= "Sal Armoniac" was an impure form of ammonium chloride. The French chemist [[Nicolas Lemery|Nicolas Lémery]] (1645–1715) discussed it in his book {{lang|fr|Cours de Chymie}} (''A Course of Chemistry'', 1675), describing where it occurs naturally and how it can be prepared artificially. It occurs naturally in the deserts of northern Africa, where it forms from puddles of animal urine. It can be prepared artificially by boiling 5 parts of urine, 1 part of sea salt, and ½ part of chimney soot until the mixture has dried. The mixture is then heated in a sublimation pot until it sublimates; the sublimated crystals are ''sal Armoniac''. See:
* Nicolas Lémery, ''Cours de chymie'' […], 7th ed. (Paris, France:  Estienne Michallet, 1688), ''Chapitre XVII : du Sel Armoniac'', [https://books.google.com/books?id=4k54-UD6uR4C&pg=PT338 pp. 338–339].
** English translation:  Nicolas Lémery with James Keill, trans., ''A Course of Chymistry'' […], 3rd ed. (London, England:  Walter Kettilby, 1698), Chap. XVII: of Sal Armoniack, p. 383, available on-line at [http://dfg-viewer.de/show/?tx_dlf%5Bid%5D=http%3A%2F%2Fdigital.ub.uni-duesseldorf.de%2Foai%2F%3Fverb%3DGetRecord%26metadataPrefix%3Dmets%26identifier%3D1882311&tx_dlf%5Bpage%5D=431&tx_dlf%5Bdouble%5D=0&cHash=c8dd26af74e251df9bd96a6e4221344b Heinrich Heine University (Düsseldorf, Germany)].}} [transl. [[ammonium chloride]]] or even sea salt".<ref name=":1" /> This combination forms a [[eutectic system]], which stabilizes its temperature automatically: 0&nbsp;°F was defined to be that stable temperature. A second point, 96&nbsp;degrees, was approximately the human body's temperature.<ref name=":1">Fahrenheit, Daniele Gabr. (1724) [https://royalsocietypublishing.org/doi/abs/10.1098/rstl.1724.0016 Experimenta & observationes de congelatione aquæ in vacuo factæ a D. G. Fahrenheit, R. S. S] (Experiments and observations on water freezing in the void by D. G. Fahrenheit, R. S. S.),
''Philosophical Transactions of the Royal Society of London'', vol.&nbsp;33, no.&nbsp;382, page&nbsp;78 (March–April 1724). Cited and translated in  http://www.sizes.com:80/units/temperature_Fahrenheit.htm.</ref> A third point, 32&nbsp;degrees, was marked as being the temperature of ice and water "without the aforementioned salts".<ref name=":1" />
According to a German story, Fahrenheit actually chose the lowest air temperature measured in his hometown [[Gdańsk|Danzig]] (Gdańsk, [[Poland]]) in winter 1708–09 as 0&nbsp;°F, and only later had the need to be able to make this value reproducible using brine.<ref>{{cite web |url=http://www.deutscher-wetterdienst.de/lexikon/index.htm?ID=L&DAT=Lufttemperatur |title = Wetterlexikon - Lufttemperatur |publisher=[[Deutscher Wetterdienst]] |access-date=13 December 2013 |language=de |url-status=dead |archive-url=https://web.archive.org/web/20131015045624/http://www.deutscher-wetterdienst.de/lexikon/index.htm?ID=L&DAT=Lufttemperatur |archive-date=15 October 2013 |df=dmy }}</ref>{{failed verification|date=December 2023}}
According to a letter Fahrenheit wrote to his friend [[Herman Boerhaave]],<ref>Ernst Cohen and W. A. T. Cohen-De Meester. ''Chemisch Weekblad'', volume 33 (1936), pages 374–393, cited and translated in http://www.sizes.com:80/units/temperature_Fahrenheit.htm.</ref> his scale was built on the work of [[Ole Rømer]], whom he had met earlier. In [[Rømer scale]], brine freezes at zero, water freezes and melts at 7.5&nbsp;degrees, body temperature is 22.5, and water boils at 60&nbsp;degrees. Fahrenheit multiplied each value by 4 in order to eliminate fractions and make the scale more [[granularity|fine-grained]]. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90&nbsp;degrees); he adjusted the scale so that the melting point of ice would be 32&nbsp;degrees, and body temperature 96&nbsp;degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval 6 times (since 64 = 2<sup>6</sup>).<ref name="TMU">{{cite book |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |last1=Frautschi |first1=Steven C. |author2=Richard P. Olenick |author3=Tom M. Apostol |author4=David L. Goodstein |title = The mechanical universe: mechanics and heat |date=14 January 2008 |page=502 }}</ref><ref>{{cite web
|url=https://www.straightdope.com/21342402/fahrenheit-scale-0-100-significance
|publisher=The Straight Dope
|title = On the Fahrenheit scale, do 0 and 100 have any special significance?
|first = Cecil |last = Adams |date=1989-12-15
}}</ref>
Fahrenheit soon after observed that water boils at about 212&nbsp;degrees using this scale.<ref>Fahrenheit, Daniele Gabr. (1724) [http://rstl.royalsocietypublishing.org/content/33/381-391/1.full.pdf+html "Experimenta circa gradum caloris liquorum nonnullorum ebullientium instituta"]. {{Webarchive|url=https://web.archive.org/web/20140629074815/http://rstl.royalsocietypublishing.org/content/33/381-391/1.full.pdf+html |date=29 June 2014 }} (Experiments performed concerning the degree of heat of some boiling liquids), ''Philosophical Transactions of the Royal Society of London'', '''33''' :  1–3.  For an English translation, see:  [https://web.lemoyne.edu/giunta/fahrenheit.html  Le Moyne College (Syracuse, New York)].</ref> The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of [[Anders Celsius]], and these fixed points were adopted by a committee of the [[Royal Society]] led by [[Henry Cavendish]] in 1776–77.<ref>[[Hasok Chang]], ''Inventing Temperature: Measurement and Scientific Progress'', pp. 8–11, Oxford University Press, 2004, {{ISBN|0198038240}}.</ref><ref>{{cite journal | title=XXXVII. The report of the Committee appointed by the Royal Society to consider of the best method of adjusting the fixed points of thermometers; and of the precautions necessary to be used in making experiments with those instruments| last1 = Cavendish | first1 = Henry
| last2 = Heberden | first2 = William
| last3 = Aubert | first3 = Alexander
| last4 = Luc | first4 = Jean Andre De
| last5 = Maskelyne | first5 = Nevil
| last6 = Horsley | first6 = Samuel
| last7 = Planta | first7 = Joseph | journal=Philosophical Transactions of the Royal Society of London| volume=67 | date=28 December 1777 | issn=0261-0523 | doi=10.1098/rstl.1777.0038|doi-access=free| url=https://archive.org/details/paper-doi-10_1098_rstl_1777_0038| pages=816–857}}</ref> Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water was exactly 32&nbsp;°F, and the boiling point was exactly 212&nbsp;°F, or 180&nbsp;degrees higher. It is for this reason that [[normal human body temperature]] is approximately 98.6&nbsp;°F (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).<ref>{{Cite journal |last1=Elert |first1=Glenn |title = Temperature of a Healthy Human (Body Temperature) |url=http://hypertextbook.com/facts/LenaWong.shtml |access-date=12 April 2008 |doi=10.1046/j.1471-6712.2002.00069.x |year=2002 |journal=Scandinavian Journal of Caring Sciences |volume=16 |pages=122–8 |pmid=12000664 |last2=Forsberg |first2=C. |last3=Wahren |first3=L.K. |issue=2 |url-status=dead |archive-url=https://web.archive.org/web/20100926162224/http://hypertextbook.com/facts/LenaWong.shtml |archive-date=26 September 2010 |df=dmy-all }}</ref>
In the present-day Fahrenheit scale, 0&nbsp;°F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above. Instead, that eutectic is at approximately 4&nbsp;°F on the final Fahrenheit scale.{{NoteTag|Eutectic temperature of ammonium chloride and water is listed as −15.9&nbsp;°C (3.38&nbsp;°F) and as −15.4&nbsp;°C (4.28&nbsp;°F) in (respectively)
* {{cite journal
|journal = J. Fluid Mech.
|last1 = Peppin|first1=S. S.|last2=Huppert|first2=H. E.|last3=Worster|first3=M. G.
|year=2008
|title = Steady-state solidification of aqueous ammonium chloride
|volume = 159
|page = 472 (table 1)
|publisher = Cambridge University Press
|doi = 10.1017/S0022112008000219
|bibcode = 2008JFM...599..465P
|s2cid = 30271164
|url=http://www.itg.cam.ac.uk/people/heh/Paper209.pdf |archive-url=https://web.archive.org/web/20100119222017/http://www.itg.cam.ac.uk/people/heh/Paper209.pdf |archive-date=2010-01-19 |url-status=live
}}
* {{cite journal
|journal = Procedia Materials Science
|doi = 10.1016/j.mspro.2014.07.288
|last1=Barman|first1= N.|last2=Nayak|first2= A. K.|last3=Chattopadhyay|first3= H.
|title = Solidification of a Binary Solution (NH<sub>4</sub>Cl + H<sub>2</sub>O) on an Inclined Cooling Plate: A Parametric Study
|volume = 7
|year = 2021
|page = 456 (table 1)
|url=https://cyberleninka.org/article/n/633625.pdf |archive-url=https://web.archive.org/web/20190115075817/https://cyberleninka.org/article/n/633625.pdf |archive-date=2019-01-15 |url-status=live
|doi-access = free
}}
}}
The [[Rankine scale|Rankine temperature scale]] was based upon the Fahrenheit temperature scale, with its zero representing [[absolute zero]] instead.
==Usage==
===General===
[[File:Countries that use Fahrenheit.svg|thumb|upright=1.25|left|Countries by usage:{{legend|#339933|Fahrenheit (°F)}}
{{legend|#66cc99|Fahrenheit (°F) and Celsius (°C)}}
{{legend|#cccccc|Celsius (°C)}}]]
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in Anglophone countries until the 1960s. In the late 1960s and 1970s, the Celsius scale replaced Fahrenheit in almost all of those countries—with the notable exception of the United States.
Fahrenheit is used in the United States, its territories and associated states (all serviced by the U.S. [[National Weather Service]]), as well as the (British) [[Cayman Islands]] and [[Liberia]] for everyday applications. The Fahrenheit scale is in use in U.S. for all temperature measurements including weather forecasts, cooking, and food freezing temperatures, however for scientific research the scale is Celsius and Kelvin.<ref>{{cite web |url=http://www.wmo.int/e-catalog/detail_en.php?PUB_ID=70&SORT=N&q=Aerodrome%20Reports%20and%20Forecasts |title=782 - Aerodrome reports and forecasts: A user's handbook to the codes |access-date=23 September 2009 |work=World Meteorological Organization}}</ref>
[[File:Thermometer CF.svg|thumb|upright]]
===United States===
Early in the 20th century, [[Frederick A. Halsey|Halsey]] and Dale suggested that reasons for resistance to use the centigrade (now Celsius) system in the U.S. included the larger size of each degree Celsius and the lower zero point in the Fahrenheit system; the Fahrenheit scale is supposedly more intuitive than Celsius for describing outdoor temperatures in temperate latitudes, with 100&nbsp;°F being a hot summer day and 0&nbsp;°F a cold winter day.<ref>{{cite book |url=https://books.google.com/books?id=xRMPAAAAYAAJ&pg=PA165 |author1=Halsey, Frederick A. |author-link1=Frederick A. Halsey |author2=Dale, Samuel S. |title=The metric fallacy |publisher=The American Institute of Weights and Measures |edition=2 |year=1919 |pages=165–166, 176–177 |access-date=19 May 2009}}</ref>
===Canada===
Canada [[Metrication in Canada|has passed legislation]] favoring the [[International System of Units]], while also maintaining legal definitions for traditional Canadian imperial units.<ref>{{cite web |url=http://laws-lois.justice.gc.ca/eng/acts/W-6/page-19.html#h-17 |title=Canadian Units of Measurement; Department of Justice, Weights and Measures Act (R.S.C., 1985, c. W-6) |access-date=5 June 2011 |date=17 May 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110513063917/http://laws-lois.justice.gc.ca/eng/acts/W-6/page-19.html#h-17 |archive-date=13 May 2011 |df=dmy }}</ref> Canadian weather reports are conveyed using degrees Celsius with occasional reference to Fahrenheit especially for [[Border blaster#Northern U.S. and Canada|cross-border broadcasts]]. Fahrenheit is still used on virtually all Canadian ovens.<ref>{{cite news |url=https://archive.seattletimes.com/archive/20000604/4024917/did-canada-go-metric-yes---and-no |title=Did Canada go metric? Yes - and no |last=Pearlstein |first=Steven |access-date=5 June 2011 |date=4 June 2000 |work=The Seattle Times}}</ref> Thermometers, both digital and analog, sold in Canada usually employ both the Celsius and Fahrenheit scales.<ref>{{cite web |url=http://www.canadiantire.ca/AST/browse/2/OutdoorLiving/GardenDecor/ClocksThermometers/PRD~0429116P/12-in.%252BThermometer%25252C%252BWhite.jsp?locale=en |title=Example of analog thermometer frequently used in Canada |access-date=6 June 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110706171604/http://www.canadiantire.ca/AST/browse/2/OutdoorLiving/GardenDecor/ClocksThermometers/PRD~0429116P/12-in.%2BThermometer%2C%2BWhite.jsp?locale=en |archive-date=6 July 2011 |df=dmy }}</ref><ref>{{cite web |url=http://www.canadiantire.ca/AST/browse/3/HouseHome/HomeDecor/Thermometers/PRD~0429929P/Deluxe%252BWeather%252BStation.jsp?locale=en |title=Example of digital thermometer frequently used in Canada |access-date=6 June 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110706171434/http://www.canadiantire.ca/AST/browse/3/HouseHome/HomeDecor/Thermometers/PRD~0429929P/Deluxe%2BWeather%2BStation.jsp?locale=en |archive-date=6 July 2011 |df=dmy }}</ref><ref name="Canadian-unit-laws">{{cite web |url=http://laws.justice.gc.ca/eng/W-6/page-2.html |archive-url=https://wayback.archive-it.org/all/20110810220840/http://laws-lois.justice.gc.ca/eng/acts/W-6/page-2.html |url-status=dead |archive-date=10 August 2011 |title=Canadian Weights and Measures Act |author=Department of Justice |publisher=Federal Government of Canada |access-date=17 July 2011 |date=26 February 2009 |df=dmy-all }}</ref>
===European Union===
In the European Union, it is mandatory to use Kelvins or degrees Celsius when quoting temperature for "economic, public health, public safety and administrative" purposes, though degrees Fahrenheit may be used alongside degrees Celsius as a supplementary unit.<ref>{{citation
|url=http://origin-www.legislation.gov.uk/uksi/2009/3046/pdfs/uksi_20093046_en.pdf
|archive-url=https://web.archive.org/web/20170101064857/http://origin-www.legislation.gov.uk/uksi/2009/3046/pdfs/uksi_20093046_en.pdf
|url-status = dead
|archive-date = 2017-01-01
|title = Statutory Instrument 2009/3046 – Weights and Measures – The Units of Measurement Regulations 2009
|quote = "The Secretary of State, being a Minister designated(a) for the purposes of section 2(2) of the European Communities Act 1972(b) in relation to units of measurement to be used for economic, health, safety, or administrative purposes, in exercise of the powers conferred by that subsection, makes the following Regulations:
}}</ref>
===United Kingdom===
Most British people use Celsius.<ref>{{cite web |date=2013-07-24 |title=The media like Fahrenheit but most Brits think in Celsius |url=https://www.opinium.com/the-media-like-fahrenheit-but-most-brits-think-in-celsius/ |access-date=2021-06-21 |website=Opinium |language=en-GB}}</ref> However, the use of Fahrenheit still may appear at times alongside degrees Celsius in the print media with no standard convention for when the measurement is included.
For example, ''[[The Times]]'' has an all-metric daily weather page but includes a Celsius-to-Fahrenheit conversion table.<ref>{{cite news
|newspaper = The Times
|date = 3 July 2013
|page = 55
|title = Weather}}</ref> Some UK tabloids have adopted a tendency of using Fahrenheit for mid to high temperatures.<ref>{{cite news |url=https://www.theguardian.com/media/greenslade/2014/dec/29/newspapers-run-hot-and-cold-over-celsius-and-fahrenheit |title=Newspapers run hot and cold over Celsius and Fahrenheit |date=29 May 2014 |newspaper=[[The Guardian]] |author=Roy Greenslade}}</ref> It has been suggested that the rationale to keep using Fahrenheit was one of emphasis for high temperatures: "−6&nbsp;°C" sounds colder than "21&nbsp;°F", and "94&nbsp;°F" sounds more sensational than "34&nbsp;°C".<ref name="T20060223">{{cite news |title=Measure for measure |date=23 February 2006 |work=The Times }}</ref>
==Unicode representation of symbol==
[[Unicode]] provides the Fahrenheit symbol at code point {{unichar|2109|degree fahrenheit}}. However, this is a [[Unicode compatibility characters|compatibility character]] encoded for [[Round-trip format conversion|roundtrip compatibility]] with legacy encodings. The Unicode standard explicitly discourages the use of this character: "The sequence {{unichar|00B0|degree sign}} + {{unichar|0046|latin capital letter f}} is preferred over {{unichar|2109|degree fahrenheit}}, and those two sequences should be treated as identical for searching."<ref>{{cite book
|title=The Unicode Standard, Version 8.0
|date=August 2015
|publisher=The Unicode Consortium
|location=Mountain View, CA, USA
|isbn=978-1-936213-10-8 |section=22.2
|url=https://www.unicode.org/versions/Unicode8.0.0/ch22.pdf |archive-url=https://web.archive.org/web/20150905122611/http://www.unicode.org/versions/Unicode8.0.0/ch22.pdf |archive-date=2015-09-05 |url-status=live
|access-date=6 September 2015}}</ref>
==See also==
{{Portal|Energy}}
* [[Outline of metrology and measurement]]
* [[Temperature conversion#Comparison of temperature scales|Comparison of temperature scales]]
* [[Degree of frost]]
== Notes ==
{{NoteFoot}}
== References ==
{{Reflist|35em}}
==External links==
* {{commons category-inline}}
* {{wiktionary-inline}}
* [https://www.britannica.com/EBchecked/topic/200226/Daniel-Gabriel-Fahrenheit Daniel Gabriel Fahrenheit (Polish-born Dutch physicist) – Encyclopædia Britannica]
* [https://enfilade18thc.com/2012/10/03/fahrenheit-thermometer-at-auction/ "At Auction | One of Only Three Original Fahrenheit Thermometers"] ''Enfilade'' page for 2012 ''[[Christie's]]'' sale of a Fahrenheit mercury thermometer
**[https://enfilade18thc.files.wordpress.com/2012/09/press-release1.pdf ''Christie's'' press release]
* {{cite journal|url=https://www.nist.gov/pml/weights-and-measures/si-units-temperature | title = SI Units - Temperature | journal = NIST | publisher = National Institute of Standards and Technology (US Department of Commerce) | date= November 15, 2019 | access-date = February 25, 2020}}
{{Scales of temperature}}
{{Imperial units}}
{{United States Customary Units}}
[[Category:Customary units of measurement in the United States]]
[[Category:Imperial units]]
[[Category:Scales of temperature]]
[[Category:1724 introductions]]
[[Category:Scales in meteorology]]