Natural gas is generally measured in one of two ways – by volume or by energy content. Gas is metered based on volume. Units typically used are cubic feet (cf), thousands of cubic feet (Mcf), millions of cubic feet (MMcf), billions of cubic feet (Bcf), and trillions of cubic feet (Tcf), or in the metric system cubic meters (cm), thousands of cubic meters (103m3), and billions of cubic meters (Bcm). But because the energy content (or heating value) of natural gas can vary, a more accurate way of measuring the ultimate value of gas is to use units based on energy content. (For example, you would need less cf of higher heating value gas for a hot shower, and conversely, more cf of lower heating value gas for the same shower.) Units commonly used include British Thermal Units (Btu), millions of Btus (MMBtu), therms (equal to 100,000 Btu), and decatherms (equal to 10 therms), or in the metric system joules or gigajoules (GJ). In some parts of the world it is also common to measure energy in kilowatt hours (kWh).
To convert volumetric units to units based on energy content, you must know the heating value of that specific gas. The heating value tells you how many MMBtus are contained in each Mcf. A common heating value is 1.015 MMBtu/Mcf. Pipelines and LDCs meter gas based on volume but then use meter factors based on average heating value to convert usage to energy content. They then bill their customers based on the energy content delivered.
bbl = Barrel
Bcm = billion cubic meters
Btu = British Thermal Unit
cm = cubic meter
Dth = decatherm
gal = Gallon
GJ = gigajoule (metric measure of energy)
Mcf = Thousand Cubic Feet
MMBtu = Million Btu
MMcf = Million Cubic Feet
toe = tons of oil equivalent
1 therm = 100,000 Btu
1 Dth = 10 therms
10 therms = 1 MMBtu
1,000,000 Btu = 1 MMBtu
1 Dth = 1 MMBtu
1000 Mcf = 1 MMcf
1000 MMcf = 1 Bcf
1 MMcf = 1,015 MMBtu*
1 MMBtu = 293 kWh
1 GJ = 0.95 MMBtu
1 bbl = 42 gal (U.S. gal)
1 bbl = 34.97 gal (Imperial gal)
1 bbl = 0.136 toe1 Bcm = 35.3 Bcf
*This conversion varies with the energy content of the gas