Gigajoules: how gas is measured
We measure natural gas by volume converted to a measure of energy. The metric standard for energy content is joules. Relating gas volume consumption to heat and temperature, approximately 4.2 joules is equal to the heat needed to raise the temperature of one gram of water by one degree Celsius at standard pressure 101.325 kPa and standard temperature (15 degrees Celsius).
Your bill is based on the amount of energy you use, measured in gigajoules or a billion joules.
- One gigajoule (GJ) equals one billion joules (J).
- A gigajoule of natural gas is about 25.5 cubic metres at standard conditions.
- One gigajoule of natural gas is approximately equivalent to 27 litres of fuel oil, 39 litres of propane, 26 litres of gasoline or 277 kilowatt hours of electricity.
- The energy content of natural gas varies because of minor variations in the amount and types of energy gases (methane, ethane, propane, butane) it contains — the more non-combustible gases in a natural gas, the lower the gigajoule value.
- The more carbon atoms in a hydrocarbon gas, the higher its gigajoule value.
Why does the energy content of natural gas vary?
Energy content of natural gas varies because natural gas has minor variations in the amount and types of energy gases (methane, ethane, propane, butane) it contains: the more non-combustible gases in the natural gas, the lower the gigajoule value. In addition, how much of any energy gas that is present in a natural gas accumulation — the mix of combustible gases — also influences the gigajoule value of natural gas. The more carbon atoms in a hydrocarbon gas, the higher its gigajoule value.
Other heating measures
Natural gas is also commonly measured in imperial units, especially in reference to gas barbecues and fireplaces. A British thermal unit (Btu) is the imperial cousin of the metric joule. A Btu is the amount of energy required to raise one pound of water one degree Fahrenheit.
Gas is sometimes measured in cubic feet at a temperature of 60 degrees Fahrenheit and an atmospheric pressure of 14.7 pounds per square inch.
Gas production from wells is discussed in terms of thousands or millions of cubic feet (Mcf and MMcf). Resources and reserves are calculated in trillions of cubic feet (Tcf).
Fast fact: How much is a trillion cubic feet? Enough to fill a cube with sides two miles long!
Note: Equipment operates at varying efficiencies. These conversion factors are strictly for the commodity, and efficiency factors are not included.