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Institute of Chemistry: Conversion of Units

About the units:

Temperature may be defined as the condition of a body which determines the transfer of heat to or from other bodies. Particularly, it is a manifestation of the average translational kinetic energy of the molecules of a substance due to heat agitation.

The customary unit of temperature is the Centigrade degree, 1/100 of the difference between the temperature of melting ice and that of water boiling under standard atmospheric pressure. The Celsius temperature scale is a designation of the scale also known as the centigrade scale. The degree Fahrenheit is 1/180, and the Réaumur 1/80 the same difference in temperature.

The fundamental temperature scale is the absolute, thermodynamic, or Kelvin scale in which the temperature measure is based on the average kinetic energy per molecule of a perfect gas. The zero of the Kelvin scale is -273.15 degrees C. The temperature scale adopted by the International Bureau of Weights and Measures is that of the constant volume hydrogen gas thermometer. The magnitude of the degree in both these scales is defined as 1/100 the difference between the temperature of melting ice and that of boiling water at 760mm pressure. Frequently, the Kelvin scale is defined as degrees C + 273.15 and the Rankine scale as degrees F + 459.6.

For more details on unit conversion, see the Chemical Rubber Company's Handbook of Chemistry and Physics.