|Unit system||Imperial/US customary|
|Named after||Daniel Gabriel Fahrenheit|
|x °F in ...||... is equal to ...|
|°C||(x − 32) × 5/ °C|
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by German physicist Daniel Gabriel Fahrenheit (1686–1736). °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.It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0
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 Bahamas, and Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Saint Kitts and Nevis 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 Cayman Islands, the British Virgin Islands, Montserrat, Anguilla, Bermuda and the Turks and Caicos Islands.
|from Fahrenheit||to Fahrenheit|
|Celsius||[°C] = ([°F] − 32) × 5⁄9||[°F] = [°C] × 9⁄5 + 32|
|Kelvin||[K] = ([°F] + 459.67) × 5⁄9||[°F] = [K] × 9⁄5 − 459.67|
|Rankine||[°R] = [°F] + 459.67||[°F] = [°R] − 459.67|
|For temperature intervals rather than specific temperatures,|
1 °F = 1 °R = 5⁄9 °C = 5⁄9 K
Comparisons among various temperature scales
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 — the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K.
The Fahrenheit scale uses the symbol ° to denote a point on the temperature scale (as does Celsius) and the letter F to indicate the use of the Fahrenheit scale (e.g. "Gallium melts at 85.5763 °F"), as well as to denote a difference between temperatures or an uncertainty in temperature (e.g. "The output of the heat exchanger experiences an increase of 72 °F" and "Our standard uncertainty is ±5 °F").
For an exact conversion, the following formulas can be applied. Here, f is the value in Fahrenheit and c the value in Celsius:
This is also an exact conversion making use of the identity −40 °F = −40 °C. Again, f is the value in Fahrenheit and c the value in Celsius:
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 (salis Armoniaci) °F was defined to be that stable temperature. The second point, 96 degrees, was approximately the human body's temperature (sanguine hominis sani, the blood of a healthy man).or even of sea salt". This combination forms a eutectic system which stabilizes its temperature automatically: 0
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, 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).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
Fahrenheit soon after observed that water boils at about 212 degrees using this scale. °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 98.2° (sic) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original 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
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.
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in English-speaking 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—typically during their general metrication process.
Fahrenheit is used in the United States, its territories and associated states (all served by the U.S. National Weather Service), as well as the Bahamas, the Cayman Islands and Liberia for everyday applications. For example, U.S. weather forecasts, food cooking, and freezing temperatures are typically given in degrees Fahrenheit. Scientists, such as meteorologists, use degrees Celsius or kelvin in all countries.
Early in the 20th century, Halsey and Dale suggested that the resistance to the use of 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.
Canada has passed legislation favoring the International System of Units, while also maintaining legal definitions for traditional Canadian imperial units.Canadian weather reports are conveyed using degrees Celsius with occasional reference to Fahrenheit especially for cross-border broadcasts. Fahrenheit is still used on virtually all Canadian ovens, and in reference to swimming pool temperatures and thermostats. Thermometers, both digital and analog, sold in Canada usually employ both the Celsius and Fahrenheit scales.
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.For example, the laundry symbols used in the United Kingdom follow the recommendations of ISO 3758:2005 showing the temperature of the washing machine water in degrees Celsius only. The equivalent label in North America uses one to six dots to denote temperature with an optional temperature in degrees Celsius.
Within the unregulated sector, such as journalism, the use of Fahrenheit in the United Kingdom follows no fixed pattern with degrees Fahrenheit often appearing alongside degrees Celsius. The Daily Mail , on its daily weather page, quotes Celsius first, followed by Fahrenheit in brackets, [ discuss ] In February 2006, the writer of an article in The Times suggested that the rationale was one of emphasis: "−6 °C" sounds colder than "21 °F" and "94 °F" sounds more impressive than "34 °C".The Daily Telegraph does not mention Fahrenheit on its daily weather page while The Times also has an all-metric daily weather page but has a Celsius-to-Fahrenheit conversion table. When publishing news stories, much of the UK press have adopted a tendency of using degrees Celsius in headlines and discussion relating to low temperatures and Fahrenheit for high temperatures.
Unicode provides the Fahrenheit symbol at code point U+2109℉DEGREE FAHRENHEIT. However, this is a compatibility character encoded for roundtrip compatibility with legacy encodings. The Unicode standard explicitly discourages the use of this character: "The sequence U+00B0°DEGREE SIGN +U+0046FLATIN CAPITAL LETTER F is preferred over U+2109℉DEGREE FAHRENHEIT, and those two sequences should be treated as identical for searching."
"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:
|Look up fahrenheit in Wiktionary, the free dictionary.|
Daniel Gabriel Fahrenheit FRS was a physicist, inventor, and scientific instrument maker. Fahrenheit was born in Danzig, then a predominantly German-speaking Hanseatic city in the Pomeranian Voivodeship of the Polish–Lithuanian Commonwealth, but lived most of his life in the Dutch Republic (1701–1736) and was one of the notable figures in the Golden Age of Dutch science and technology.
The Rankine scale is an absolute scale of thermodynamic temperature named after the Glasgow University engineer and physicist William John Macquorn Rankine, who proposed it in 1859. It may be used in engineering systems where heat computations are done using degrees Fahrenheit.
A thermometer is a device that measures temperature or a temperature gradient. A thermometer has two important elements: (1) a temperature sensor in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value. Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.
Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics.
Timeline of temperature and pressure measurement technology. A history of temperature measurement and pressure measurement technology.
The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen gas or it may be at less than atmospheric pressure, a partial vacuum.
The Réaumur scale, also known as the "octogesimal division", is a temperature scale for which the freezing and boiling points of water are defined as 0 and 80 degrees respectively. The scale is named for René Antoine Ferchault de Réaumur, who first proposed a similar scale in 1730.
The Rømer scale, also known as Romer or Roemer, is a temperature scale named after the Danish astronomer Ole Christensen Rømer, who proposed it in 1701. It is based on the freezing point of pure water being 7.5 degrees and the boiling point of water as 60 degrees.
The Delisle scale (°D) is a temperature scale invented in 1732 by the French astronomer Joseph-Nicolas Delisle (1688–1768). Delisle was the author of Mémoires pour servir à l'histoire et aux progrès de l'Astronomie, de la Géographie et de la Physique (1738).
The Newton scale is a temperature scale devised by Isaac Newton in 1701. He called his device a "thermometer", but he did not use the term "temperature", speaking of "degrees of heat" instead. Newton's publication represents the first attempt to introduce an objective way of measuring temperature . Newton likely developed his scale for practical use rather than for a theoretical interest in thermodynamics; he had been appointed Warden of the Mint in 1695, and Master of the Mint in 1699, and his interest in the melting points of metals are likely inspired by his duties in connection with the Royal Mint.
The term degree is used in several scales of temperature. The symbol ° is usually used, followed by the initial letter of the unit, for example “°C” for degree(s) Celsius. A degree can be defined as a set change in temperature measured against a given scale, for example, one degree Celsius is one hundredth of the temperature change between the point at which water starts to change state from solid to liquid state and the point at which it starts to change from its gaseous state to liquid.
The International Temperature Scale of 1990 (ITS-90) published by the Consultative Committee for Thermometry (CCT) of the International Committee for Weights and Measures (CIPM) is an equipment calibration standard for making measurements on the Kelvin and Celsius temperature scales. ITS-90 is an approximation of the thermodynamic temperature scale that facilitates the comparability and compatibility of temperature measurements internationally. It specifies fourteen calibration points ranging from 0.65±0 K to 1357.77±0 K and is subdivided into multiple temperature ranges which overlap in some instances. ITS-90 is the latest of a series of International Temperature Scales adopted by CIPM since 1927. Adopted at the 1989 General Conference on Weights and Measures, it supersedes the International Practical Temperature Scale of 1968 and the 1976 "Provisional 0.5 K to 30 K Temperature Scale". CCT has also adopted a mise en pratique in 2011. The lowest temperature covered by ITS-90 is 0.65 K. In 2000, the temperature scale was extended further, to 0.9 mK, by the adoption of a supplemental scale, known as the Provisional Low Temperature Scale of 2000 (PLTS-2000).
A medical thermometer is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue, under the armpit, into the rectum via the anus, into the ear, or on the forehead.
A degree of frost is a non-standard unit of measure for air temperature meaning degrees below melting point of water. "Degree" in this case can refer to degree Celsius or degree Fahrenheit.
The Celsius scale, also known as the centigrade scale, is a temperature scale used by the International System of Units (SI). As an SI derived unit, it is used worldwide. In the United States, the Bahamas, Belize, the Cayman Islands and Liberia however, Fahrenheit remains the preferred scale for everyday temperature measurement. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and gradus, which means steps.
The kelvin is the base unit of temperature in the International System of Units (SI), having the unit symbol K. It is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907).
Temperature is a physical quantity that expresses the subjective sensations of hot and cold. Temperature is measured with a thermometer.
An absolute scale is a system of measurement that begins at a minimum, or zero point, and progresses in only one direction. An absolute scale differs from an arbitrary, or "relative," scale, which begins at some point selected by a person and can progress in both directions. An absolute scale begins at a natural minimum, leaving only one direction in which to progress.
Scale of temperature is a way to measure temperature quantitatively. Empirical scales measure the quantity of heat in a system in relation to a fixed parameter, a thermometer. They are not absolute measures, that is why scales vary. Absolute temperature is thermodynamic temperature because it is directly related to thermodynamics. It is the Zeroth Law of Thermodynamics that leads to a formal definition of thermodynamic temperature.
Jean-Pierre Christin was a French physicist, mathematician, astronomer and musician. His proposal in 1743 to reverse the Celsius thermometer scale was widely accepted and is still in use today.