Gas meter readings convert to kWh by taking the volume of gas you used, multiplying it by the calorific value on your bill and a fixed correction factor of 1.02264, then dividing by 3.6. This guide explains each step of the gas meter reading to kWh conversion for UK homes, including the extra step for older imperial meters, so you can check your supplier’s bill line by line and work out what the gas actually cost.
Quick answer: Subtract your previous reading from the latest one to get the gas used. For a metric meter, multiply the cubic metres by the calorific value on your bill (about 39.5), then by the correction factor 1.02264, and divide by 3.6. Imperial meters: multiply units by 2.83 first. One cubic metre is roughly 11.2 kWh.
What is the formula to convert a gas meter reading to kWh?
The formula is: kWh = cubic metres used × calorific value × 1.02264 ÷ 3.6. British Gas and E.ON Next both publish this same formula, and it comes from the way UK law defines the energy content of gas sold to homes.
- Find the gas used. Latest reading minus previous reading, recording only the digits your supplier asks for in its meter reading guide.
- Convert to cubic metres if needed. Imperial meters measure in hundreds of cubic feet, so multiply the units by 2.83.
- Multiply by the calorific value (CV) shown on your bill, in megajoules per cubic metre.
- Multiply by the correction factor 1.02264.
- Divide by 3.6 to turn megajoules into kilowatt hours.
Then multiply the kWh by your unit rate to get the cost, and add the daily standing charge for the number of days in the period.
What does each number in the gas conversion mean?
Each of the three fixed or published numbers has a specific job, and knowing them helps you spot errors on a bill.
Calorific value (usually 37 to 43)
The calorific value tells you how much heat the gas produces when it burns, in megajoules per cubic metre. British Gas gives a typical range of 37 to 43 MJ/m³, and your bill shows the figure actually used, normally in the section that explains how your gas was converted to kWh. It varies slightly over time, which is why each bill shows the figure that was used.
Correction factor (1.02264)
Gas expands and contracts with temperature and pressure, so the same amount of energy can take up a slightly different volume. The Gas (Calculation of Thermal Energy) Regulations 1996 require volumes to be converted to standard conditions of 15°C and 1013.25 millibars. Suppliers account for this on household bills with a fixed correction factor of 1.02264, as British Gas and E.ON Next explain.
Dividing by 3.6
One kilowatt hour equals 3.6 megajoules, so dividing by 3.6 converts the energy from megajoules into the kWh units that appear on your bill. The same regulations use 3.6 for kilowatt hours and 105.505 for therms.
How many kWh are in a cubic metre of gas?
One cubic metre of gas is roughly 11 kWh, and about 11.2 kWh at a calorific value of 39.5. The exact figure depends on the CV on your bill, as the table shows.
| Calorific value (MJ/m³) | kWh per 1 m³ | kWh per 100 m³ |
|---|---|---|
| 37.0 | 10.51 | 1,051.0 |
| 38.5 | 10.94 | 1,093.7 |
| 39.0 | 11.08 | 1,107.9 |
| 39.5 | 11.22 | 1,122.1 |
| 40.0 | 11.36 | 1,136.3 |
| 41.0 | 11.65 | 1,164.7 |
| 43.0 | 12.21 | 1,221.5 |
All figures use the 1.02264 correction factor and the divisor of 3.6. Use this as a quick sense check: if your bill shows far more than about 11 kWh for every cubic metre you used, ask your supplier to explain.
How do you convert an imperial gas meter reading to kWh?
Multiply the units used on an imperial meter by 2.83 to get cubic metres, then use the normal formula. Imperial meters record gas in cubic feet, and British Gas describes the conversion as multiplying cubic feet by 0.0283. Imperial readings are usually recorded in hundreds of cubic feet, which is why E.ON Next gives a multiplier of 2.83 for that unit.
Your bill normally states whether the meter is metric or imperial, and the meter face shows the unit it measures in. Using the wrong one is an easy mistake to make, and it matters because it changes the answer by a factor of almost three. If in doubt, ask your supplier to confirm the meter type.
For example, if an imperial meter moved by 35 units, that is 35 × 2.83 = 99.05 m³. At a CV of 39.5, that gives 99.05 × 39.5 × 1.02264 ÷ 3.6 = about 1,111 kWh.
How do you work out the cost from kWh?
Multiply the kWh by your unit rate, then add the standing charge for every day in the billing period. Under the Ofgem energy price cap for 1 October to 31 December 2026, the average direct debit gas rates in England, Scotland and Wales are 7.97p per kWh and a 29.68p daily standing charge. Your own tariff may be different, and the cap is reviewed every 3 months, so use the rates on your bill.
Example: a metric meter read 4520 at the last bill and 4620 thirty days later. That is 100 m³ used. The bill shows a calorific value of 39.5.
- Energy: 100 × 39.5 × 1.02264 ÷ 3.6 = 1,122.06 kWh
- Gas used: 1,122.06 kWh × 7.97p = £89.43
- Standing charge: 30 days × 29.68p = £8.90
- Total for the period: about £98.33
You can reproduce this in our gas bill calculator, which takes the two readings, the meter type, the calorific value, the number of days and your rates. If your bill lists VAT separately, check whether the rates you entered already include it. The other energy bill calculators use the same price cap figures.
Why might your own calculation not match your bill?
Small differences of a few kWh are normal, but large gaps usually come from one of five causes.
- Estimated readings. If the bill says a reading was estimated, the supplier has guessed it rather than read your meter. Submit a real reading.
- Wrong meter type. Treating an imperial meter as metric, or the reverse, changes the result by nearly three times.
- Different calorific value. Use the CV printed on that bill, not a generic figure.
- Extra digits. Recording more digits than your supplier’s reading guide asks for inflates the reading.
- Rate changes mid-period. If the price cap or your tariff changed during the billing period, part of the gas is charged at each rate.
Smart meters send readings automatically, but a gas meter still records the volume of gas, so you can take the readings from the meter and check them with the same formula.
Gas meter reading to kWh FAQs
How do I convert gas units to kWh?
Subtract the previous reading from the latest one, convert to cubic metres if your meter is imperial (multiply by 2.83), then multiply by the calorific value and 1.02264 and divide by 3.6. The answer is the energy you used in kWh.
What calorific value should I use?
Use the calorific value printed on your gas bill for that period. It typically sits between 37 and 43 megajoules per cubic metre, according to British Gas. If you do not have a bill, 39.5 is a reasonable example figure for a rough estimate.
Why is the correction factor 1.02264?
UK rules convert gas volumes to standard conditions of 15°C and 1013.25 millibars, because gas volume changes with temperature and pressure. Suppliers allow for this on household bills with the fixed factor 1.02264, as British Gas and E.ON Next explain.
How do I know if my gas meter is metric or imperial?
Check your gas bill, which normally states the meter type, or look at the unit shown on the meter face. Metric meters measure in cubic metres and imperial meters in cubic feet. Imperial readings need multiplying by 2.83 before using the kWh formula.
How many kWh of gas does a house use a day?
It varies widely with the season, the size of the home, insulation and how you heat water. The best way to find your own figure is to take two readings a few days apart, convert the difference to kWh and divide by the number of days.
Do smart meters convert gas to kWh?
A smart gas meter still records the volume of gas used and sends it to your supplier automatically. Your bill is still worked out in kWh, so you can check the figures yourself using the formula in this guide.
Checked October 2026. Sources: The Gas (Calculation of Thermal Energy) Regulations 1996, British Gas: How to convert gas m3 to kWh, E.ON Next: Convert gas units to kWh, Ofgem: Energy price cap unit rates and standing charges.
