Gas conversion factor
What is the gas conversion factor?
Gas meters record volume. UK gas bills are priced in energy. Bridging the two needs a conversion, and the working figure that does the job is the gas conversion factor. It bundles the volume correction factor (around 1.02264, to adjust for temperature and pressure at the meter) and the calorific value (around 39.5 MJ/m³, divided by 3.6 to get kWh) into a single multiplier that converts cubic metres straight to kWh. The typical UK value is around 11.1 kWh per m³, though the exact figure for your bill depends on your Local Distribution Zone, the daily CV applied, and whether your meter is imperial or metric.
Conversion factors are applied on every business gas bill in Great Britain to turn the cubic metres your meter records into the kWh you actually pay for.
On this page
- What the gas conversion factor does
- The two components inside the factor
- Typical UK conversion factor value
- How the factor is shown on bills
- Conversion for imperial gas meters
- Worked example of the conversion
- How daily CV variation affects the factor
- Why the conversion factor matters
- Auditing the conversion on your bill
- How the factor relates to AQ and SOQ
- FAQs
The gas conversion factor is sometimes referred to on bills as a combined number, sometimes broken out into volume correction and CV separately. Either way, understanding how it works helps when you are checking a gas bill, planning an energy budget, or comparing gas usage across periods.
What the gas conversion factor does
The conversion factor turns the volume reading on your gas meter into the energy value used to bill you.
- Volume from the meter is in cubic metres (m³) for modern meters or hundreds of cubic feet for older imperial meters.
- The conversion factor multiplies the volume to produce kilowatt-hours (kWh).
- The kWh figure is then multiplied by the unit rate to give the variable cost on the bill.
Without the conversion factor, a UK gas bill could not connect what the meter records to what the customer pays.
The two components inside the factor
The gas conversion factor is built from two separate pieces.
- Volume correction factor (VCF). Adjusts the raw meter reading for temperature and pressure differences between the meter location and standard reference conditions. The UK default VCF is 1.02264.
- Calorific value (CV). Reflects the energy content of the gas being delivered, in megajoules per cubic metre. Typical UK gas CV is around 39.5 MJ/m³.
Multiplying VCF by CV and dividing by 3.6 (to convert MJ to kWh) gives the combined gas conversion factor in kWh per cubic metre.
Typical UK conversion factor value
Plugging the typical UK numbers into the formula.
| Component | Typical UK value |
|---|---|
| Volume correction factor | 1.02264 |
| Calorific value | 39.5 MJ/m³ |
| Conversion (VCF × CV ÷ 3.6) | (1.02264 × 39.5) ÷ 3.6 = 11.221 kWh/m³ |
The combined factor sits in a narrow range of 10.9 to 11.4 kWh/m³ for almost every UK gas supply, day to day and LDZ to LDZ.
How the factor is shown on bills
UK gas bills handle the conversion in a few different ways.
- Itemised conversion chain. The bill shows volume, volume correction, CV, and the final kWh separately, with the arithmetic visible.
- Combined factor. Some bills show a single “Conversion factor: 11.1 kWh/m³” line that bundles everything.
- Volume-to-kWh only. A minimal bill shows volume used and total kWh, with the conversion not explained.
Itemised bills are easier to validate. Combined-factor bills are quicker to scan but harder to audit. If your supplier offers a bill format choice and you want to validate regularly, choose the itemised format.
Conversion for imperial gas meters
Older UK gas meters measure in hundreds of cubic feet rather than cubic metres. The conversion chain has an extra step.
- Multiply the hundreds-of-cubic-feet reading by 2.83 to get cubic metres.
- Apply the volume correction factor (1.02264).
- Multiply by the CV in MJ/m³.
- Divide by 3.6 to get kWh.
So 100 cubic feet of UK gas works out to about 31.7 kWh after the full conversion chain. Imperial meters are now uncommon but still in service in some older premises.
Worked example of the conversion
Illustrative example. A small commercial site records 800 cubic metres of gas in a quarter. The published CV for the LDZ that quarter averaged 39.4 MJ/m³.
| Step | Calculation | Value |
|---|---|---|
| Volume from meter | 800 m³ | 800 m³ |
| Volume correction | 800 × 1.02264 | 818.11 m³ |
| Energy in MJ | 818.11 × 39.4 | 32,233 MJ |
| Convert to kWh | 32,233 ÷ 3.6 | 8,953.6 kWh |
| Effective conversion factor | 8,953.6 ÷ 800 | 11.19 kWh/m³ |
| Variable cost at 8 p/kWh | 8,953.6 × 0.08 | £716.29 |
Example only. Real bills apply the daily CV to the share of volume consumed each day rather than the quarterly average. The point is the structure of the conversion, not the precise number.
How daily CV variation affects the factor
The combined conversion factor changes day to day because CV changes day to day.
- A CV of 38.5 MJ/m³ gives a conversion of 10.94 kWh/m³.
- A CV of 39.5 MJ/m³ gives 11.22 kWh/m³.
- A CV of 40.5 MJ/m³ gives 11.50 kWh/m³.
Over a year the variation within an LDZ is typically within a couple of per cent. For most operational uses this is noise. For very large industrial consumers or precision reporting it can move the kWh totals enough to matter.
Why the conversion factor matters
The conversion factor sits inside three different bill questions.
- Bill arithmetic. The factor is the link from meter volume to billed kWh. Wrong factor produces wrong kWh, which produces wrong cost.
- Year-on-year comparisons. Comparing this year’s gas consumption to last year’s in kWh involves the conversion factor for both periods. If CV has moved, the kWh comparison shifts even if real consumption has not.
- Cross-site comparisons. Comparing two sites in different LDZs in kWh involves slightly different conversion factors at each end. Comparing volumes (m³) is more apples-to-apples than comparing kWh in this case.
Auditing the conversion on your bill
A simple sanity check on any gas bill.
- Take the volume in cubic metres from the bill.
- Multiply by 11.2 (the typical UK combined conversion).
- The result should be within a couple of per cent of the kWh on the bill.
- If the gap is wider, look at the daily CV figures and volume correction applied.
The deeper gas billing article on the Clearsight site, How Gas Is Converted to kWh, walks through the same calculation in more detail.
How the factor relates to AQ and SOQ
The conversion factor sits underneath several other gas-billing concepts.
- Annual Quantity (AQ). The annual kWh estimate for a meter. AQ is calculated by Xoserve from actual reads converted via the same conversion chain.
- SOQ (Supply Offtake Quantity). The daily maximum kWh on larger sites, again derived from volume measurements via the conversion factor.
- Standing charge. Independent of the conversion factor. The factor only affects the variable kWh element of the bill.
Related entries. kWh, calorific value, volume correction, Annual Quantity (AQ), therm, MPRN, bill validation.
Frequently asked questions
What is the gas conversion factor?
The multiplier UK gas suppliers use to convert the volume of gas your meter records into the kilowatt-hours of energy you are billed for. It bundles volume correction and calorific value into a single working number, typically around 11.1 kWh per cubic metre.
What goes into the conversion factor?
Two components. Volume correction factor (1.02264, adjusting for temperature and pressure at the meter) and calorific value (typically 39.5 MJ/m³ for UK gas). Multiplying and dividing by 3.6 gives the combined factor in kWh per cubic metre.
What is the typical UK conversion factor?
Around 11.2 kWh per cubic metre. The exact value depends on the daily calorific value published for the Local Distribution Zone and varies slightly day to day.
How is the conversion factor shown on my bill?
Three common formats. Some bills itemise volume, volume correction, CV, and kWh separately. Some show a combined “Conversion factor: 11.1 kWh/m³” line. Some show only the volume and total kWh without explanation.
How do I convert hundreds of cubic feet to kWh?
Multiply by 2.83 to convert to cubic metres, then apply volume correction (1.02264), then CV in MJ/m³, then divide by 3.6. The combined factor works out to about 31.7 kWh per 100 cubic feet of UK gas.
Why does the conversion factor change?
Because the calorific value of UK gas varies day to day with the mix of gas being delivered (North Sea, interconnectors, LNG, biomethane, storage). Daily CV updates feed into the daily conversion factor.
Does my standing charge depend on the conversion factor?
No. The standing charge is a fixed daily amount independent of consumption and unaffected by the conversion factor. The factor only affects the variable kWh element of the bill.
Can I check the conversion factor used on my bill?
Yes. Multiply your volume in m³ by 11.2 (the typical UK combined factor). The result should be within a couple of per cent of the kWh on the bill. Wider gaps warrant looking at the daily CV figures and the volume correction applied.
What is the difference between volume correction and calorific value?
Volume correction adjusts for temperature and pressure at the meter (so the measured volume reflects gas at standard conditions). Calorific value reflects the energy content of the gas. Both are needed to convert raw meter readings into billable kWh.
How does the conversion factor relate to therms?
A therm is a fixed energy unit (29.31 kWh). The conversion factor decides how many cubic metres of gas equal one therm. At a conversion factor of 11.2 kWh/m³, 1 therm equals about 2.62 m³ of gas.
Is the conversion factor the same across the UK?
No. Each LDZ has its own published CV that reflects the gas mix in that area. The combined conversion factor varies slightly between LDZs and day to day within each LDZ.
Does AQ use the conversion factor?
Yes. Annual Quantity (AQ) is the kWh estimate for a meter, derived from actual reads converted via the same chain (volume correction times CV divided by 3.6). The factor is implicit in the AQ calculation.
Why does the kWh on my smart gas meter sometimes differ from the bill?
Smart meters apply an internal conversion factor that may use slightly different defaults to the supplier’s bill calculation. Small differences are normal. Material gaps warrant raising a query with the supplier.
Can I see the daily CV used in my bill?
Most UK suppliers will provide the daily CV figures on request, and the National Gas data portal publishes them per LDZ. They are not usually itemised on the customer bill but are available to anyone who asks.