British thermal unit

British thermal units, or BTUs, are a unit of energy. It is the amount of energy required to heat a pound of water by one degree Fahrenheit at one atm.

The BTU is defined as 251.9958 calories, and due to the calorie having many different accepted values, so does the BTU. These different values of the BTU include:[1]

thermochemical Btu 1 Btu = 1054.35 J
59 °F (15 °C) Btu 1 Btu = 1054.80 J
International Table Btu 1 Btu = 1055.06 J
mean Btu 1 Btu = 1055.87 J

The International Table BTU is the value that is most commonly accepted in most modern energy publications,[2] so this will be the value being used whenever the BTU is referred to anywhere in this website.

BTU per hour (BTU/hr) is a measurement of power, and is more commonly used than BTU. Most house furnaces are rated in BTU/hr.


For Further Reading


  1. American Physical Society. Energy Units [Online]. Available:
  2. U.S. Department of Energy, Annual Energy Review 1995, Energy Information Administration Report DOE/EIA-0384(95) (Washington, D.C.: U.S. DOE, 1996).

Authors and Editors

Allison Campbell, Jordan Hanania, James Jenden, Ellen Lloyd, Jasdeep Toor, Jason Donev
Last updated: June 25, 2018
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