Degrees Fahrenheit (°F) Unit Definition

At the end of the 2010s, Fahrenheit was used as the official temperature scale only 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 Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Saint Kitts and Nevis, the Bahamas, and Belize use Fahrenheit and Celsius. All other countries in the world officially now use the Celsius scale, named after Swedish astronomer Anders Celsius. A handful of British Overseas Territories still use Fahrenheit alongside Celsius including the British Virgin Islands, Montserrat, Anguilla, and Bermuda.

On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point is 212 °F (at standard atmospheric pressure). This puts the boiling and freezing points of water 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water are 100 degrees apart. A temperature interval of 1 °F is equal to an interval of 5⁄9 degrees Celsius. The Fahrenheit and Celsius scales intersect at −40° (i.e., −40 °F = −40 °C).

Absolute zero is −273.15 °C or −459.67 °F. The Rankine temperature scale uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0 °R. This is similar to the way that the Kelvin (K) temperature scale matches the Celsius scale, except that absolute zero is 0 K.

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by German physicist Daniel Gabriel Fahrenheit (1686–1736). Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and a salt (ammonium chloride). Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature (96 °F, about 2.6 °F less than the modern value due to a later redefinition of the scale). The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.

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, of water, and of ammonium chloride or even of sea salt". This combination forms a eutectic system which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. The second point, 96 degrees, was approximately the human body's temperature (for the blood of a healthy man).

According to a story in Germany, Fahrenheit actually chose the lowest air temperature measured in his hometown Danzig in winter 1708/09 as 0 °F, and only later had the need to be able to make this value reproducible using brine.

According to a letter Fahrenheit wrote to his friend Herman Boerhaave, his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more 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 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).

Fahrenheit soon after observed that water boils at about 212 degrees using this scale. 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. Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98.6° (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).

In the present-day Fahrenheit scale, 0 °F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above. Instead, that eutectic is at approximately 4 °F on the final Fahrenheit scale.

The Rankine temperature scale was based upon the Fahrenheit temperature scale, with its zero representing absolute zero instead.

• Absolute zero (exactly): -459.67 °F

• Boiling point of liquid nitrogen: -320.44 °F

• Sublimation point of dry ice: -108.40 °F

• Intersection of Celsius and Fahrenheit scales: -40 °F

• Melting point of H2O (purified ice): 32 °F

• Room temperature (NIST standard): 68 °F

• Normal human body temperature (average): 98.60 °F

• Waters boiling point at 1 atm (101.325 kPa) (approximate: see Boiling point): 211.97 °F

Here are the conversion formulas used to convert both from and to degrees fahrenheit:

• Degrees Celsius or Centigrade (°C)
• Degrees Delisle (°De)
• Degrees Fahrenheit (°F)
• Degrees Newton (°N)
• Degrees Rankine (°Ra)
• Degrees Réaumur (°Ré)
• Degrees Rømer (°Rø)
• Kelvin (K)

• Degrees Celsius or Centigrade (°C)
• Kelvin (K)

Though every effort has been made to test this unit converter, we are not to be held liable for any special, incidental, indirect or consequential damages or monetary losses of any kind arising out of or in connection with the use of any of the converter tools and information sourced from this website. This unit converter is provided as a service to you, please use at your own risk. Do not use calculations for anything where loss of life, money, property, etc could result from inaccurate unit conversions.

For more information: please see our full disclaimer.

“Fahrenheit.” Wikipedia, Wikimedia Foundation, 4 Apr. 2020, en.wikipedia.org/wiki/Fahrenheit.