British Thermal Unit

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What Does British Thermal Unit Mean?

A British thermal unit (BTU) is a standard measure of thermal energy. A single BTU is the amount of energy required to increase the temperature of one pound (avoirdupois)of water by one degree Fahrenheit (F).


The BTU is a non-metric unit of energy utilized mostly in the United States and sometimes in the United Kingdom (UK). Many other countries use the joule (J) which is a unit of energy based on the international system of units (SI). One BTU is equal to around 1055 joules (or 1055 watt-seconds).

In computers the BTU is used to measure the amount of output in heat generating devices. The heat output is conveyed in BTU’s per hour (BTU/h). One watt of heat dissipation is equal to 3.7 BTU/h.

Techopedia Explains British Thermal Unit

A British thermal unit (BTU) is the amount of energy or heat needed to increase the temperature of one pound of water by one degree Fahrenheit (F) at its maximum density. The maximum density transpires at a temperature of 39.1 degrees °F.

One BTU is about the equivalent of the following:

1055 joules
1.054 to 1.060 kilojoules (kJ)
107.5 kilogram-meters
0.293071 watt hours (W.h)
778 to 782 foot-pounds force (ft·lbf)
252 to 253 calories “little calories”
0.25 kilocalories (kcal) ‘large calories”
With many heating and cooling systems thousands of BTU’s can be produced. In order to simplify measurements when in the thousands or millions, other BTU standards are used:

MBTU: Equal to one thousand (1,000) BTU
MMBTU: Equal to one million (1,000,000) BTU
Therm: Equal to 100,000 or 10 BTU (U.S. uses BTU59°F and the European Union uses BTUIT)
Quadrillion (quad): Equal to 1,000,000,000,000,000 or 1015 BTU
The BTU is frequently used for measuring energy producing and energy transferring systems such as air conditioners, ovens, refrigerators and heaters. Often the energy output of computer devices is configured to regulate temperatures of large buildings. The heat output of computer equipment is generally measured in BTU/h with 3.7 BTU/h equal to 1 watt of energy.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.