About the Gas Meter Reading to kWh Calculator
This gas meter reading calculator converts the units on your gas meter into kilowatt hours (kWh) — the unit your gas is billed in — and estimates the cost. Enter your previous and current readings, say whether your meter is metric (cubic metres) or imperial (hundreds of cubic feet), and add the calorific value from your bill. The calculator applies the same legal formula UK suppliers use and then multiplies by your unit rate and daily standing charge.
Use it to check an estimated bill, to work out what you have used since your last reading, or to keep track of usage between monthly statements. It also shows the volume in cubic metres and the energy in therms, which helps if you are comparing with a US-style bill.
Defaults use the Ofgem price cap gas rates for 1 October–31 December 2026 (7.97p per kWh and 29.68p per day, GB average Direct Debit including 5% VAT) and a typical calorific value of 39.5 MJ/m³. The calorific value varies slightly by area and month — it is printed on your bill, usually between about 37.5 and 43 MJ/m³. If your reading has gone down because the meter rolled over past all nines, the calculator allows for that.
With the default inputs, the gas used is 1,122.1 kWh. Change any value above to recalculate instantly.
How to use the gas meter reading to kwh calculator
- 1Choose whether your meter reads in cubic metres (usually says m³) or cubic feet (ft³).
- 2Enter the previous and current readings — whole numbers only, ignoring red digits after the decimal point.
- 3Enter the calorific value from your bill (or keep 39.5).
- 4Enter your unit rate, standing charge and the days between readings.
- 5Read the kWh used and the total cost.
Formula and method
Under the Gas (Calculation of Thermal Energy) Regulations 1996, the energy billed is the corrected volume of gas multiplied by its calorific value and divided by 3.6 to convert megajoules to kilowatt hours. For household meters the volume is corrected to standard temperature (15°C) and pressure (1013.25 mbar) with a fixed factor of 1.02264.
Metric meters read in cubic metres, so the units used are the volume. Imperial meters read in hundreds of cubic feet, so the units are multiplied by 2.8317 to get cubic metres. Cost is kWh × unit rate plus days × standing charge. Therms are kWh ÷ 29.3071 (one therm is 100,000 Btu).
- 1.02264
- Volume correction factor for temperature and pressure
- CV
- Calorific value of the gas in MJ per m³ (on your bill)
- 3.6
- Megajoules per kilowatt hour
- 2.83
- Cubic metres per 100 cubic feet (imperial meter unit)
Worked examples
100 m³ on a metric meter over 30 days
100 m³ × 1.02264 × 39.5 ÷ 3.6 = 1,122 kWh. At 7.97p per kWh the gas costs £89.43, and 30 days of 29.68p standing charge adds £8.90, for £98.33 in total.
Imperial meter, 40 units
An imperial meter counts hundreds of cubic feet, so 40 units is 4,000 ft³ or 113.27 m³. Applying the correction factor and a 39.5 MJ/m³ calorific value gives about 1,271 kWh.
A winter quarter in London
250 m³ at a calorific value of 39.2 is 250 × 1.02264 × 39.2 ÷ 3.6 = 2,784 kWh. At London’s capped 8.15p per kWh that is £226.88, plus £27.48 for 91 days of standing charges.
Frequently asked questions
How do I convert gas units to kWh?+
For a metric meter, multiply the cubic metres used by 1.02264 and by the calorific value (about 39.5), then divide by 3.6. As a rule of thumb, one cubic metre of gas is roughly 11.2 kWh. For an imperial meter, first multiply the units by 2.83.
How do I know if my gas meter is metric or imperial?+
Metric meters show “m³” next to the reading and usually have five digits before a decimal point. Imperial meters show “ft³” or “cubic feet” and typically have four digits. Older meters are more likely to be imperial.
What is the calorific value on my gas bill?+
It measures how much energy is in each cubic metre of gas, in megajoules. Gas transporters measure it daily and suppliers bill an average. In Great Britain it is usually around 38–41 MJ/m³ and is printed on your bill.
What is the 1.02264 correction factor?+
It adjusts the measured volume to standard conditions of 15°C and 1013.25 millibars so everyone pays for the same quantity of gas. It is set in the Gas (Calculation of Thermal Energy) Regulations 1996 for household-sized meters.
Should I include the red numbers on my meter?+
No. Suppliers only use the whole numbers — the black or white digits before the decimal point. Red digits or those after the decimal point show fractions of a unit and are ignored for billing.