Btu conversion factors
|Energy source||Physical units and Btu
|Electricity||1 kilowatthour = 3,412 Btu
|Natural gas|| 1 cubic foot = 1,025 Btu
1 therm = 100,000 Btu
|Motor gasoline||1 gallon = 120,524 Btu²|
|Diesel fuel||1 gallon = 138,690 Btu|
|Heating oil||1 gallon = 138,690 Btu|
|Propane||1 gallon = 91,333 Btu|
|Wood||1 cord = 20,000,000 Btu³|
1Weighted averages across different contexts of each fuel such as imports, exports, production, and consumption.
2Gasoline sold at retail in the United States, with about 10% ethanol content by volume.
3This is estimated. 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.
The Btu conversion factors above are approximations. The U.S. Energy Information Administration also provides specific heat contents for fuels and electricity.
What is a British thermal unit?
A British thermal unit (Btu) is a measure of the heat content of fuels. It is the quantity of heat required to raise the temperature of 1 pound of liquid water by 1 degree Fahrenheit at the temperature that water has its greatest density (approximately 39 degrees Fahrenheit).
Why use British thermal units?
Energy or heat content can be used to compare different 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. EIA uses British thermal units as a unit of energy content.
Using British thermal units to compare fuels for electricity generation
Fuels are sold in different physical units, but prices can be compared in dollars per million Btu by dividing the price per unit by the energy content per unit. This shows which fuel is the least expensive.
|Price||Btu (energy content)||$/Million Btu|
|Coal||$47.51 per ton||19.59 million per short ton||$2.43|
|Oil||$133.44 per barrel||6.04 million per barrel||$22.11|
|Natural gas||$3.81 thousand cubic feet (Mcf)||1.02 million per Mcf||$3.74|
Based on the unit prices and heat contents in the table above, coal is the least expensive fuel on a price-per-energy content basis.
Of course, fuel price is not the only factor to consider when selecting a particular fuel. The efficiency of the device (generator, car engine, or household combustion appliance) burning the fuel will determine how much of the fuels heat content is converted to useful energy (electricity, horsepower, or space heat). Environmental emissions and equipment costs are other factors that should also be taken into account.
British thermal unit quick facts
A single Btu is insignificant in terms of the amount of energy used by a single household or by an entire country. In 2013, the United States used about 98 quadrillion (written out, 1 quadrillion is a 1 followed by 15 zeros) Btu of energy.