What is a British thermal unit?
British thermal unit (Btu) is a measure of the heat content of fuels or energy sources. One Btu is the quantity of heat required to raise the temperature of one pound of liquid water by 1° Fahrenheit (F) at the temperature that water has its greatest density (approximately 39° F).
A single Btu is very small in terms of the amount of energy a single household or an entire country uses. In 2021, the United States used about 97.33 quadrillion Btu of energy. Written out, 1 quadrillion is a 1 followed by 15 zeros: 1,000,000,000,000,000.
Why use British thermal units?
You can use energy, or heat content, to compare energy sources or fuels on an equal basis. Fuels can be converted from physical units of measure (such as weight or volume) to a common unit of measurement of the energy or heat content of each fuel. The U.S. Energy Information Administration (EIA) uses Btu as a unit of energy content.
EIA collects data on the physical amounts (volume or weight) of energy sources produced, imported, exported, and consumed. EIA converts those amounts into Btu equivalents to compare the sources on an equal basis.
For example, the physical volumes of fossil fuels consumed in the United States in 2022 and Btu equivalents were:
- Petroleum—7.40 billion barrels—35.85 quadrillion Btu
- Natural gas—32.31 trillion cubic feet—33.41 quadrillion Btu
- Coal—512.64 million short tons—9.85 quadrillion Btu
Sample Btu conversion factors
| Energy source/fuel | Physical units and Btu1 |
|---|---|
| Electricity | 1 kilowatthour = 3,412 Btu |
| Natural gas | 1 cubic foot = 1,036 Btu2 1 therm = 100,000 Btu |
| Motor gasoline | 1 gallon = 120,214 Btu3 |
| Diesel fuel | 1 gallon = 137,381 Btu4 |
| Heating oil | 1 gallon = 138,500 Btu5 |
| Propane | 1 gallon = 91,452 Btu |
| Wood | 1 cord = 20,000,000 Btu6 |
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1 Btu factors are for end-use consumption in 2022 from Monthly Energy Review, May 2023, excluding wood; preliminary data for 2022. 2 Natural gas consumed by end-use sectors (excluding electric power sector). 3 Finished motor gasoline sold at retail in the United States, including fuel ethanol content. 4 Distillate fuel with 15 parts per million (ppm) sulfur or less sulfur content. 5 Distillate fuel with 15 ppm to 500 ppm sulfur content. 6 This conversion is an estimate. A cord of wood is a volume unit and does not take wood density or moisture content into account. Wood heat content varies significantly with moisture content. |
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The Btu conversion factors above are approximate. Tables with heat content for fuels and electricity are available in the appendices of the Monthly Energy Review.
Last updated: June 29, 2023, with preliminary data for 2022.