The energy content of a natural gas depends on its composition, which means there is no universal conversion factor between volume and energy. Residential natural gas customers get a measure known as therms on their bills. One therm is equivalent to 100,000 BTUs. In the natural gas industry, MBTUs, which is the short form for one million BTUs, are also sometimes used to compare the energy content between various natural gas and fuels.

In 2009, on a daily basis, the average American home consumed 193 cubic feet of natural gas. Determining whether natural gas or heating oil is more efficient is a good exercise in energy efficiency. Assuming a 1025 BTU per cubic foot natural gas and that 81,300 cubic foot is consumed in a year, a total of 83,332,500 BTUs is consumed. Compare this to consuming 584 gallons of heating oil at 138,690 BTU per gallon, which yields 80,994,496 BTU. In this example scenario, natural gas is less efficient than heating oil at heating the home. The cost of the electricity can then be computed based on the total BTUs and a decision made on which fuel to use.