Raumthermometer Fahrenheit+Celsius.jpg
Thermometer with Fahrenheit (marked on outer bezel) and Celsius (marked on inner dial) degree units.
General information
Unit systemImperial/US customary
Unit ofTemperature
Named afterDaniel Gabriel Fahrenheit
x °F in ...... corresponds to ...
   SI base units   5/9(x +459.67) K
   SI derived units   5/9(x − 32) °C
   Imperial/US absolute scale   x + 459.67 °Ra

The Fahrenheit scale (/ˈfærənˌht, ˈfɑːr-/) is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736).[1] 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 °F, was established as the freezing temperature of a solution of brine made from a mixture of water, ice, and ammonium chloride (a salt).[2][3] The other limit established was his best estimate of the average human body temperature, originally set at 90 °F, then 96 °F (about 2.6 °F less than the modern value due to a later redefinition of the scale).[2]

For much of the 20th century, the Fahrenheit scale was defined by two fixed points with a 180 °F separation: the temperature at which pure water freezes was defined as 32 °F and the boiling point of water was defined to be 212 °F, both at sea level and under standard atmospheric pressure. It is now formally defined using the Kelvin scale[4][5] and hence ultimately by the Boltzmann constant, the Planck constant, and the second (defined as a specific number of cycles of the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom.)[6]

It continues to be officially used in the United States (including its unincorporated territories), its freely associated states in the Western Pacific (Palau, the Federated States of Micronesia and the Marshall Islands), the Cayman Islands, and the former American colony of Liberia. Fahrenheit is used alongside the Celsius scale in Antigua and Barbuda and other countries which use the same meteorological service, such as Saint Kitts and Nevis, the Bahamas, and Belize. A handful of British Overseas Territories, including the Virgin Islands, Montserrat, Anguilla, and Bermuda, still use both scales.[7] All other countries now use Celsius ("centigrade" until 1948), a scale formalized about 20 years after the Fahrenheit scale. The United Kingdom started to change from Fahrenheit to Celsius in 1962, and many people remain aware of Fahrenheit temperatures; degrees Fahrenheit are sometimes used in newspaper headlines to sensationalize heatwaves.[8]

  1. ^ Balmer, Robert T. (2010). Modern Engineering Thermodynamics. Academic Press. p. 9. ISBN 978-0-12-374996-3. Retrieved 17 July 2011.
  2. ^ a b "Fahrenheit temperature scale". Encyclopædia Britannica Online. Retrieved 25 September 2015.
  3. ^ "Fahrenheit: Facts, History & Conversion Formulas". Live Science. Retrieved 9 February 2018.
  4. ^ Benham, Elizabeth (6 October 2020). "Busting Myths about the Metric System". US National Institute of Standards and Technology (NIST).
  5. ^ "Appendix C – General Tables of Units of Measurement" (PDF). NIST Handbook 44 -Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices - 2022. US National Institute of Standards and Technology (NIST). 29 November 2021. Archived (PDF) from the original on 27 December 2021.
  6. ^ "Resolution 1 of the 26th CGPM (2018)". Bureau International des Poids et Mesures. Retrieved 7 January 2022.
  7. ^ "50 years of Celsius weather forecasts – time to kill off Fahrenheit for good? | Metric Views". Archived from the original on 2 October 2020. Retrieved 28 July 2019.
  8. ^ "Newspapers run hot and cold over Celsius and Fahrenheit". The Guardian. 29 December 2014.