Try the formula with your own numbers
Energy equivalent
m³ × × 1.02264 ÷ 3.6
ft³ × 0.0283 × × 1.02264 ÷ 3.6
At 7.8 p/kWh*
£
*Indicative business gas unit rate
1.02264
Volume correction factor
Standard 15°C, 1013.25 mbar.
38.5–41
CV range, MJ/m³
Check the line on your bill.
÷ 3.6
MJ to kWh divisor
1 kWh = 3.6 megajoules.
Why suppliers charge in kWh, not m³
A cubic metre of gas does not deliver a fixed amount of energy. Natural gas drawn from the North Sea is slightly different from gas piped through the Interconnector or unloaded as LNG at Milford Haven. Each blend has its own calorific value, and that value also varies with how much nitrogen, propane and butane the network is dosing on a given day to keep the heating value within the regulated band of 37.5 to 43.0 MJ/m³.
Charging in cubic metres would mean two customers buying the same volume could be getting different amounts of energy. Charging in kWh fixes the problem: a kilowatt-hour is always 3.6 megajoules of heat, regardless of where the molecule came from. The conversion is what turns your raw volume reading into the energy figure your supplier actually invoices.
The formula, decomposed
Every UK supplier applies the same calculation, prescribed by The Gas (Calculation of Thermal Energy) Regulations 1996. The four factors below are the building blocks.
Metric meter (m³)
Read directly off the dial. Five-digit displays are always metric. Used in every UK new-build since the 1990s.
Imperial meter (ft³)
Four-digit displays, often labelled "cu ft". Multiply by 2.83 if the dial reads in hundreds, or 28.3 in thousands.
Worked example: a metric meter
Two readings, one subtraction, one calculation. Here is the full sequence for a typical small business.
-
1
Previous reading: 1,000 m³
-
2
Current reading: 1,100 m³
-
3
Volume used: 1,100 − 1,000 = 100 m³
-
4
Apply the formula: 100 × 39.5 × 1.02264 ÷ 3.6 = 1,122 kWh
Using a calorific value of 39.5 MJ/m³. Your result will differ slightly if your bill shows a different CV.
Worked example: an imperial meter
The imperial calculation has one extra step at the start: convert the cubic-foot reading into cubic metres, then apply the same formula as above.
- 1Volume used: 100 ft³
- 2Convert to m³: 100 × 0.0283 = 2.83 m³
- 3Apply the formula: 2.83 × 39.5 × 1.02264 ÷ 3.6 = 31.8 kWh
If the dial face shows "×100" or "×1000", multiply your raw reading by that factor before step 1.
Quick reference table
Approximate kWh equivalents at a calorific value of 39.5 MJ/m³ and the standard correction factor of 1.02264.
| Gas volume | m³ equivalent | kWh (approx.) |
|---|---|---|
| 10 m³ | 10.00 | 112 |
| 50 m³ | 50.00 | 561 |
| 100 m³ | 100.00 | 1,122 |
| 500 m³ | 500.00 | 5,612 |
| 1,000 m³ | 1,000.00 | 11,224 |
| 100 ft³ | 2.83 | 32 |
| 1,000 ft³ | 28.30 | 318 |
| 10,000 ft³ | 283.00 | 3,176 |
How to check your gas bill is correct
Once the conversion is second nature, the workflow for verifying a bill takes two minutes. Pull three numbers off the bill, the meter readings, the calorific value, and the unit rate (p/kWh), then run them through the formula. Multiply the resulting kWh by the unit rate and compare to the cash total shown.
Most discrepancies come from estimated readings, flagged with an "E" next to the figure on the bill. Estimates have to be plausible but not accurate, so a supplier can overstate consumption for 18 months before a smart meter or an in-person read corrects it. Submitting actual readings monthly removes the problem entirely.
The five conversion mistakes that show up in audits
Energy auditors see the same handful of errors on hundreds of business bills. Avoiding them keeps your conversion within 1% of the regulated figure.
- Mixing units: using the m³ formula on a cubic-foot reading throws the answer off by a factor of 35 ;
- Ignoring the multiplier: some imperial dials display readings to be multiplied by 100 or 1,000, look for the label ;
- Using a generic CV: the actual value on your bill can be 38.2 or 41.0, the difference is 7% ;
- Skipping 1.02264: omitting the correction factor understates the energy by 2.3% ;
- Trusting estimated readings: "E" markers on a bill can hide a 20% over- or under-charge.
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Frequently asked questions
Multiply your cubic-metre reading by the calorific value on your bill (around 39.5 MJ/m³ in 2026), then by the volume correction factor 1.02264, then divide by 3.6. The formula gives you the energy equivalent in kilowatt-hours, ready to multiply by your unit rate to verify the cash total on your bill.
Gas expands with temperature and shrinks with pressure. The factor 1.02264 standardises every meter reading to a reference condition of 15°C and 1013.25 millibars, so a kWh of energy bills the same in Cornwall in August as in Aberdeen in February. The number is set by The Gas (Calculation of Thermal Energy) Regulations 1996 and is identical for every UK meter, domestic or commercial.
Every gas bill carries a line marked "calorific value" or "CV", expressed in megajoules per cubic metre. In 2026 most UK regions show a CV between 38.5 and 41.0 MJ/m³, with a national average just under 39.5. National Grid publishes a daily figure for each Local Distribution Zone, and your supplier averages it over the billing period.
Metric meters display readings in m³ and show five digits. Imperial meters show readings in cubic feet (ft³) with four digits, often with a "×100" or "×1000" multiplier label. New installations have been metric-only since 1995, so imperial meters are increasingly rare and usually found in older industrial sites or pre-1990s buildings.
Yes. The inverse is: m³ = (kWh × 3.6) ÷ (calorific value × 1.02264). Plug in any kWh figure on your bill, and the result is the equivalent volume the meter would have registered. This is useful for cross-checking estimated bills, where suppliers sometimes invert the formula sloppily and produce a meter reading that does not match the meter.
Mixing up metric and imperial readings. Using the m³ formula on a ft³ value produces a result roughly 35 times too high ; the other way round, it lands 35 times too low. The second most common error is forgetting the ×100 multiplier on older imperial meters, which understates consumption by two orders of magnitude. Always check the unit label printed on the meter face before running the calculation.