Gas units to kWh: the UK formula on every gas bill
Gas meters measure volume, but British gas is sold by the kilowatt hour. This gas units to kWh calculator turns two meter readings — or a number of units — into kWh exactly as a supplier does, then prices them with your unit rate, standing charge and VAT so you can check a bill, estimate one before it arrives or see what a cold month cost.
It handles metric meters that read in cubic metres and older imperial meters that count hundreds of cubic feet, and shows each step of the conversion so you can follow it line by line against your statement.
How to use the Gas Units to kWh Calculator (UK)
- Choose the meter type. A metric meter says m³ on its face; an imperial meter says ft³ or cubic feet and normally counts in hundreds.
- Enter the previous and current readings (black digits only), or switch to Units used if you already know the difference.
- Type the calorific value printed on your bill — the default 39.5 MJ/m³ is only an example. Leave the correction factor at 1.02264.
- Add your unit rate in pence per kWh, the daily standing charge, the number of days and VAT (5 % for households).
- Read the kWh and the cost, check each step in the table and copy the working if you want to raise a query with your supplier.
Gas Units to kWh Calculator (UK) features
The official formula
Volume × 1.02264 × calorific value ÷ 3.6 — the method suppliers must follow for household meters.
Metric and imperial meters
Hundreds of cubic feet are converted with the × 2.83 factor used on bills, and single cubic feet with × 0.0283.
A full bill estimate
Unit rate, standing charge per day, number of days and VAT give the total and the average cost per day.
Reading checks
A current reading below the previous one is flagged, because it usually means a misread digit or a replaced meter.
Copyable working
Every step, from units to pounds, can be copied as plain text.
The gas units to kWh formula
kWh = volume in m³ × 1.02264 × calorific value ÷ 3.6. The volume correction factor 1.02264 adjusts the metered volume to standard conditions (15 °C and 1,013.25 mbar); it is the conversion factor set by the Gas (Calculation of Thermal Energy) Regulations 1996 (SI 1996/439, as amended in 1997) for supply points expected to use no more than 732,000 kWh a year — every home. Larger sites use a calculated temperature, pressure and compressibility factor instead.
The calorific value (CV) is the energy in a cubic metre of gas, in megajoules. Dividing megajoules by 3.6 gives kWh, because one kilowatt hour is 3.6 MJ. Worked example with the defaults: 2,931.0 − 2,841.0 = 90 m³; 90 × 1.02264 = 92.04 m³; × 39.5 = 3,635.5 MJ; ÷ 3.6 = 1,009.9 kWh.
Imperial meters: hundreds of cubic feet
An imperial meter usually counts in hundreds of cubic feet, so the units used are first multiplied by 2.83 to get cubic metres (100 ft³ is 2.8317 m³; bills round it to 2.83). Then the same formula applies: 32 units × 2.83 = 90.56 m³, × 1.02264 × 39.5 ÷ 3.6 ≈ 1,016 kWh. If your meter counts single cubic feet, the factor is 0.0283. Picking the wrong meter type makes the result a hundred times — or almost three times — out, which is a common cause of shock bills.
Where the calorific value comes from
National Gas Transmission works out a daily average calorific value for each charging area and publishes it, rounded to one decimal place, on its data portal (data.nationalgas.com). Ofgem’s guidance to suppliers (5 August 2014) says the CV used for billing must be the average of those daily figures over the billing period, truncated — not rounded — to one decimal place. That is why the CV on your bill changes slightly from one bill to the next; values in Great Britain are typically around 38–40 MJ/m³.
| Calorific value (MJ/m³) | kWh per m³ | kWh per 100 ft³ unit |
|---|---|---|
| 38.0 | 10.79 | 30.55 |
| 39.0 | 11.08 | 31.35 |
| 39.5 | 11.22 | 31.75 |
| 40.0 | 11.36 | 32.16 |
Gas Units to kWh Calculator (UK) FAQ
How do I convert gas units to kWh?
Subtract the previous reading from the current one, convert to cubic metres if your meter is imperial (× 2.83 for hundreds of cubic feet), multiply by 1.02264 and by the calorific value on your bill, then divide by 3.6. The gas units to kWh calculator does every step and shows them.
How many kWh is one unit of gas in the UK?
On a metric meter one unit is one cubic metre: about 11.2 kWh at a calorific value of 39.5 MJ/m³. On an imperial meter one unit is 100 cubic feet: about 31.7 kWh at the same calorific value.
What is the 1.02264 on my gas bill?
It is the volume correction factor. Gas expands and contracts with temperature and pressure, so the law fixes a standard factor of 1.02264 for household meters to convert the measured volume to standard conditions before the energy is worked out.
Why does the calorific value on my bill change?
Gas from different sources holds slightly different energy. The calorific value is measured every day for each area and your supplier uses the average over your billing period, truncated to one decimal place.
Is my meter metric or imperial?
Look at the face: metric meters say m³ or “cubic metres” and usually have five black digits before a decimal point; imperial meters say ft³ or “cubic feet” and usually have four black digits. If you are unsure, ask your supplier — the bill also states the meter type.
Is this exactly what my supplier will charge?
It uses the same formula, but your supplier may use a slightly different average calorific value, estimate readings, or round at different stages, and prices change. Use it to check that a bill is in the right range, not as a guarantee.