Natural gas can be measured in a number of different ways. As a gas, it can be measured by the volume it takes up at normal temperatures and pressures, commonly expressed in cubic feet. Production and distribution companies commonly measure natural gas in thousands of cubic feet (Mcf), millions of cubic feet (MMcf), or trillions of cubic feet (Tcf). While measuring by volume is useful, natural gas can also be measured as a source of energy. Like other forms of energy, natural gas is commonly measured and expressed in British thermal units (Btu). One Btu is the amount of natural gas that will produce enough energy to heat one pound of water by one degree at normal pressure. To give an idea, one cubic foot of natural gas contains about 1,027 Btus. When natural gas is delivered to a residence, it is measured by the gas utility in ‘therms’ for billing purposes. A therm is equivalent to 100,000 Btu, or just over 97 cubic feet, of natural gas.

In terms of using compressed natural gas for vehicular fuel, it is commonly converted to a “gas gallon equivalent” (GGE) to put it into a unit of measure that consumers can easily relate to. One GGE equals 5.660 lbs of natural gas, or 1.14 Therms, or 114, 118.8 Btus, or 127 standard cubic feet. One Mcf (one thousand cubic feet) of natural gas will make approximately 7.9 GGE of vehicular fuel. Typically a vehicle will travel the same distance on one GGE of natural gas as it would have on one gallon of gasoline.