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Units and calculators explained  

Understanding energy units

Energy comes in many forms, and we use different fuels—such as natural gas, oil, coal, and electricity—for various purposes, from heating our homes to powering our vehicles. Physical units measure:

  • Distance
  • Area
  • Volume
  • Height
  • Weight
  • Mass
  • Force
  • Energy

We use different physical units to measure different types of energy or fuels. Some examples include:

Unit Energy types
Barrels (b) or gallon (g)  Gasoline, diesel fuel, jet fuel, and biofuels
Cubic feet (cf)  Natural gas
Short ton (st)  Coal
Kilowatthours (kWh)  Electricity

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Barrel equivalents for different fuel types

For example, 1 barrel of:
Crude oil or petroleum products  42 U.S. gallons
Portland cement  376 pounds
Flour  196 pounds
Pork or fish  200 pounds
U.S. dry measure (grain, for example)  3.29122 bushels or 4.2104 cubic feet

Units for comparing energy

To compare fuels with each other, we need to convert their measurements to the same unit. We can compare different types of energy using units such as British thermal units (Btu), barrels of oil equivalent, metric tons of oil equivalent, metric tons of coal equivalent, or terajoules.

In the United States, Btu is the most common unit for comparing energy sources or fuels. A Btu measures heat energy. The Btu content of fuels varies slightly from country to country because the fuels come from different places, giving them slightly different characteristics.

Using conversion factors, we can compare different fuels and fuel costs. Each year, these factors are recalculated to account for changes in the quality and composition of the fuels.

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
1Current conversion factors are updated annually in Appendix A of the Monthly Energy Review.

Examples of converting energy sources in different physical units to Btu


Example 1:

You have a natural gas furnace in your home that used 67,000 cubic feet of natural gas for heating last winter. Your neighbor’s furnace burns heating oil, which used 500 gallons last winter. You can convert the natural gas and heating oil units into Btus to find out who used more energy for heating.

  • Natural gas
  • 67,000 cubic feet (your home)
  • x
  • 1,036 Btu per cubic foot
  • =
  • 69,412,000 Btu
  • Heating oil
  • 500 gallons (neighbor's home)
  • x
  • 137,381 Btu per gallon
  • =
  • 68,690,476 Btu

Result: You used more energy to heat your home.

Example 2:

You and your same neighbor want to compare the cost of heating your homes. You can compare the average fuel prices over the winter (October through March) by dividing the average natural gas and heating oil monthly prices per unit by the Btu content of the fuels in million Btu.

  • Natural gas
  • $13.66 per thousand cubic feet
  • ÷
  • 1.036 million Btu per thousand cubic feet
  • =
  • $13.18 per million Btu
  • Heating oil
  • $4.11 per gallon
  • ÷
  • 0.137381 million Btu per gallon
  • =
  • $29.90 per million Btu

Result: The price per million Btu for natural gas is less than half the price of heating oil per million Btu.