Different types of energy are measured by different physical units: barrels or gallons for petroleum; cubic feet for natural gas; tons for coal; kilowatt-hours for electricity. To compare different fuels, we need to convert the measurements to the same units. Some popular units for comparing energy include: British Thermal Units (Btu), barrels of oil equivalents, metric tons of oil equivalents, metric tons of coal equivalents, and terajoules. In the United States, the British thermal unit (Btu), a measure of heat energy, is the most commonly used unit for comparing fuels. Because energy used in different countries comes from different places, the Btu content of fuels varies slightly from country to country. The Btu content used in the energy calculations reflect the average energy contents for fuels consumed in the United States.
The following table shows the BTU energy content and other factors, as published in the Federal Register on March 21, 2007:
The last column shows the equivalent Therms per the normal unit of measure used to purchase each energy source. To put it another way, the table shows that 0.9133 Therms of Natural Gas has the same BTU content as a gallon of Propane, or 1.39 Therms of Natural Gas has the same BTU content as a gallon of #2 Fuel Oil.
If I use 100 Gallons of Propane how much Natural gas would I use to equal this usage:
100 Gallons * .9133 Therms/Gallon = 91.33 Therms of Natural Gas