Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. Named after its inventor. Daniel Fahrenheit

To detailed of an answer, so let me link you to the winki: http://en.wikipedia.org/wiki/Fahrenheit Me thinks the man made it far too complicated ;-)

1) Originally, Daniel Gabriel Fahrenheit (1686–1736) based his scale on *three* reference points of temperature: - 0°F was the temperature of a frigorific mixture of ice, water and ammonium chloride - 32°F was the temperature of still water as ice is just forming on the surface - 96°F was the temperature measured in the mouth or under the armpit. 2) Later, other scientists decided to redefine the scale as follows: - 32°F is the temperature of still water as ice is just forming on the surface - 212°F is the temperature of boiling water (no further point is needed) As this was done, it was possible to have a simple correnspondence with the Celsius scale, which was defined at that time using 0°C and 100°C for those two points. Source and further information: http://en.wikipedia.org/wiki/Fahrenheit 3) In the meantime, the Celsius scale is defined more accurately based on absolute zero and and on the triple point of "VSMOW", which is pure water with a specific isotopic composition. Further information: http://en.wikipedia.org/wiki/Celsius http://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water As the Fahrenheit scale is no more used for scientific use, a more accurate definition is not needed.