What is a British thermal unit?
British thermal unit (Btu) measures the heat content of fuels or energy sources. One Btu is the amount of heat needed to raise the temperature of one pound of water by 1° Fahrenheit (F). A single Btu is very small in terms of the amount of energy a single household or an entire country uses.
Although a single Btu represents a small amount of energy, the total energy consumed by households or entire nations typically reaches quadrillions of Btu (quad). For example, the United States' total energy consumption in recent years has often been in the quadrillions. A quadrillion is a substantial number: 1,000,000,000,000,000 (a 1 followed by 15 zeros).
Why use British thermal units?
Different energy sources and fuels use different units of measure. For example, heating oil is measured in gallons and natural gas is measured in cubic feet. If you wanted to compare the two, you would need to convert them to the same unit. You can use heat content to compare energy sources or fuels.
We use the Btu as the standard unit for measuring and comparing energy content. We collect data on the volume or weight of energy sources produced, imported, exported, and consumed. We convert those amounts into Btu equivalents to compare them equally.
Using conversion factors, we can compare different fuels and fuel costs. Each year, those factors are recalculated to account for changes in the quality and composition of the fuels. For example, historical physical volumes of fossil fuels consumed in the United States and their Btu equivalents were:
Sample fossil fuel Btu conversion factors1
| Fossil fuel type | Physical amount | Btu equivalent |
|---|---|---|
| Petroleum | 7.40 billion barrels | 35.43 quads |
| Natural gas | 32.51 trillion cubic feet | 33.61 quads |
| Coal | 425.92 million short tons | 8.17 quads |
| 1You can find current tables with heat content for fuels and electricity in Appendix A of the Monthly Energy Review. | ||
Sample Btu conversion factors1
| Energy source/fuel | Physical units and Btu |
|---|---|
| Electricity | 1 kilowatthour=3,412 Btu |
| Natural gas | 1 cubic foot=1,036 Btu 1 therm=100,000 Btu |
| Motor gasoline | 1 gallon=120,214 Btu |
| Diesel fuel | 1 gallon=137,381 Btu |
| Heating oil | 1 gallon=138,500 Btu |
| Propane | 1 gallon=91,452 Btu |
| Wood | 1 cord=20,000,000 Btu |
| 1You can find current tables with heat content for fuels and electricity in Appendix A of the Monthly Energy Review. | |