Gas conversion formula

What is the formula?

Cubic meters to kilowatt hours

If your meter has m3 on the reading display, then gas is delivered in cubic meters.

To convert gas usage from cubic meters (m3) to kilowatt hours (kWh), you would take 2 readings and the difference between the two readings would be the usage. For example, if the reading on 10th April is 00455 and the reading on 10th May is 00575, the difference is 120, which indicates the usage during that period.

You would then multipy the number for usage by the volume correction factor, which is typically 1.022640, then multiply again by the calorific value, which is between 37.5 and 43, but we would simply use 40, and then you would divide by the kWh conversion factor, which is always 3.6.

In this example, we would calculate the kWh used as:

00575 – 00455 = 120

120 x 1.022640 x 40 / 3.6 = 1,364

This means that 120 cubic meters have been used or that 1,364 kilowatt hours have been used.

Cubic feet to kilowatt hours

If your meter has ft3 on the reading display, then gas is delivered in cubic feet.

There are 2.83 cubic feet to a cubic meter.

Therefore, you would calculate as above, then multiply by 2.83 to get to the correct figure for kilowatt hours if your gas is delivered in cubic feet (ft3).

What is the volume correction factor?

The volume correction factor takes into consideration the temperature, pressure and atmospheric conditions at a given property. This factor is typically 1.02264 unless your property has unusual atmospheric conditions. 

What is the calorific value?

The calorific value (CV) is a measure of how much heat the gas creates when it burns. It is measured in megajoules per cubic meter (MJ/m3). A gas supply generally has a CV of between 37.5 and 43.0 MJ/m3. Gas transporters are required by Ofgem to maintain this figure within 38 MJ/m³ to 41 MJ/m³ as figures outside of this range may cause problems with gas burning appliances. You can use 40.0 as a default number for calculations if you don’t know the exact figure.

What is the kWh conversion factor?

The kWh conversion factor converts gas from m3 to kWh. The figure is always 3.6.