Gas Meter Reading to kWh Calculator

Your gas meter measures volume, but your bill charges energy. This calculator applies the same conversion your supplier does, so you can check a bill against your own readings or work out what a period of use actually came to.

Enter the reading at the start and end of the period. If your bill prints a calorific value, use it — that is the figure you were charged against.

Why gas is billed in kWh

Gas meters record how much gas passed through them, in cubic metres or cubic feet. But a cubic metre of gas does not always carry the same amount of energy — that depends on the composition of the gas in the network at the time, which varies by region and by season.

Billing in kilowatt hours means you pay for energy delivered rather than volume delivered, so a change in gas composition does not quietly change what you get for your money. It also puts gas and electricity in the same unit, which is what makes comparing the two possible at all.

The conversion formula

kWh = (cubic metres × 1.02264 × calorific value) ÷ 3.6

There are three steps in that line:

• The volume correction factor of 1.02264 adjusts for the temperature and pressure at which the gas was delivered, so that your cubic metre is comparable to a standard one.
• The calorific value is how much energy that gas actually carried, in megajoules per cubic metre. It is printed on your bill for the period concerned.
• Dividing by 3.6 converts megajoules to kilowatt hours, because one kilowatt hour is 3.6 megajoules.

Metric and imperial meters

Metric meters read directly in cubic metres, so the difference between two readings is the volume used.

Older imperial meters are calibrated in hundreds of cubic feet. A reading difference of 10 is 1,000 cubic feet, not 10. That factor of a hundred is the most common mistake in a manual conversion, and it understates a bill by two orders of magnitude when it is missed.

An imperial meter usually has fewer dials than a metric one and often says “cubic feet” or “ft³” on the face. If in doubt, check whether your bill quotes cubic metres or cubic feet.

Checking your bill

If your figure and your supplier's differ noticeably, the usual causes are a different calorific value, an estimated rather than actual reading, or a billing period that does not match the dates you used.

An estimated reading is worth ruling out first. Bills marked “E” rather than “A” are the supplier's guess, and submitting an actual reading corrects them.

To turn these kilowatt hours into money, use the gas bill calculator, which takes your unit rate and standing charge. For what gas costs across the market, see the gas market data page.