Encyclopedia  |   World Factbook  |   World Flags  |   Reference Tables  |   List of Lists     
   Academic Disciplines  |   Historical Timeline  |   Themed Timelines  |   Biographies  |   How-Tos     
Sponsor by The Tattoo Collection
British thermal unit
Main Page | See live article | Alphabetical index

British thermal unit

The British thermal unit (Btu, BTU) is a nonmetric unit of energy, used in the United States and, to a certain extent, the UK. The SI unit is the joule (J), which is used by most other countries. 1 Btu is defined by the amount of heat required to raise the temperature of one pound avoirdupois of water from 63 F to 64 F. It is often used to describe the heat value of fuels and heating and cooling system capacities.

1 Btu is approximately:

252 calories,
778 ft.·lbf.,
1,055 joules

A unit called the quad is defined as 1015 BTUs, which is about 1.055 × 1018 joules, and the therm is defined in the United States and European Union as 100,000 BTU.

The Btu should not be confused with the Board of Trade Unit (B.O.T.U.), which is a much larger quantity of energy.

See also: conversion of units, metrication