Fahrenheit Fahrenheit ( symbol °F ) is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit ( 1686 – 1736 ) , after whom the scale is named . Within this scale , the freezing of water into ice is defined at 32 degrees , while the boiling point of water is defined to be 212 degrees — on Fahrenheit ' s original scale the freezing point of brine was zero degrees . By the end of the 20th century , most countries used the Celsius scale rather than the Fahrenheit scale , though Canada retains it as a supplementary scale that can be used alongside Celsius . Fahrenheit remains the official scale in several countries : United States , Cayman Islands , Palau , Bahamas and Belize . The Rankine temperature scale was based upon the Fahrenheit temperature scale , with its zero representing absolute zero instead . Definition and conversions . On the Fahrenheit scale , the freezing point of water is 32 degrees Fahrenheit ( °F ) and the boiling point 212 °F ( at standard atmospheric pressure ) . This puts the boiling and freezing points of water exactly 180 degrees apart . Therefore , a degree on the Fahrenheit scale is 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 degrees Celsius . The Fahrenheit and Celsius scales intersect at −40° ( −40 °F and −40 °C represent the same temperature ) . 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 . Like Celsius , the Fahrenheit scale uses the symbol ° to denote a point on the temperature scale 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 " ) . History . Fahrenheit proposed his temperature scale in 1724 , basing it on three reference points of temperature . In his initial scale ( which is not the final Fahrenheit scale ) , the zero point is determined by placing the thermometer in brine : he used a mixture of ice , water , and ammonium chloride , a salt , at a 1 : 1 : 1 ratio . This is a frigorific mixture which stabilizes its temperature automatically : that stable temperature was defined as 0 °F ( −17 . 78 °C ) . The second point , at 32 degrees , was a mixture of ice and water without the ammonium chloride at a 1 : 1 ratio . The third point , 96 degrees , was approximately the human body temperature , then called " blood - heat " . 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 increase the granularity of the scale . 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 observed that water boils at about 212 degrees using this scale . Later , other scientists decided to redefine the scale slightly to make the freezing point exactly 32 °F , and the boiling point exactly 212 °F or 180 degrees higher . It is for this reason that normal human body temperature is approximately 98° ( oral temperature ) on the revised scale ( whereas it was 90° on Fahrenheit ' s multiplication of Rømer , and 96° on his original scale ) . Usage . 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 ( known until 1948 as " centigrade " ) replaced Fahrenheit in almost all of those countries , typically during their metrication process . Fahrenheit is used in the United States , Belize , Palau and the United States territories of Puerto Rico , Guam and the U . S . Virgin Islands 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 Celsius or Kelvin in all countries . In some nations , both measures are quoted . Early in the twentieth 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 favouring 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 trans border broadcasts . Virtually all Canadian ovens make legal use of the Fahrenheit scale . Thermometers , both digital and analogue , sold in Canada usually employ both the Celsius and Fahrenheit scales . Also , in some instances , ( swimming pool temperature or cooking temperatures in Québec for example ) temperatures are still expressed in Fahrenheit . Fahrenheit also remains in occasional use in the United Kingdom , with some newspaper and online weather reports quoting temperatures in both Celsius and Fahrenheit ( or having an option to enable this ) , especially during record - breaking weather . However , TV weather reports are primarily conveyed using degrees Celsius . Cooking instructions on some ( but not all ) packaged food retain dual temperature scales for the benefit of consumers using older ovens , and dual - unit thermometers are readily available . Unicode representation of symbol . The Fahrenheit symbol has its own Unicode character : " ℉ " ( U + 2109 ) . This is a compatibility character encoded for roundtrip compatibility with legacy CJK encodings ( which included it to conform to layout in square ideographic character cells ) and vertical layout . Use of compatibility characters is discouraged by the Unicode Consortium . The ordinary degree sign ( U + 00B0 ) followed by the Latin letter F ( " °F " ) is thus the preferred way of recording the symbol for " degree Fahrenheit " .