Whilst your gas meter measures gas usage in cubic meters, your usage is actually billed in ‘megajoules’ or ‘units’ on your bill, depending on your state.
To calculate the number of megajoules, you must subtract your meter’s end read from the start read, then multiply by pressure factor and heating value.
For WA, the number of Megajoules is then divided by 3.6 to get to billed units.
A unit of gas is equivalent to 1 kilowatt hour of energy.
The pressure and speed of the natural gas delivered to your property will often vary and is based on environmental factors, such as temperature and the appliance that is consuming the gas.