How to convert gas units to kWh (UK)

Use your meter reading (m³ or ft³) plus your bill’s calorific value and correction factor to convert gas units into kWh — the unit your supplier uses to price your gas.

  • Works for metric (m³) and imperial (ft³) meters
  • Includes the exact UK conversion formula suppliers use
  • Two realistic examples with numbers and common pitfalls
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Figures are illustrative. Your bill’s calorific value and unit rates vary by supplier, region and tariff.

Fast answer: how to convert gas units to kWh

To convert gas units to kWh, use this UK billing formula: kWh = volume used × correction factor (1.02264) × calorific value ÷ 3.6. If your meter is in ft³ (imperial), first convert to m³ by multiplying by 0.0283. Use the calorific value shown on your bill.

Most important number

Correction factor is usually 1.02264 on UK gas bills.

What you need

Your opening/closing meter readings and the calorific value printed on your statement.

Why it matters

Suppliers price gas per kWh, not per m³/ft³ — conversion explains your bill and helps you check charges.

Quick caveat: Your kWh result may differ slightly from our examples because calorific value varies by day and region, and suppliers may round at different steps.

The UK gas unit-to-kWh formula (step-by-step)

UK suppliers convert gas volume into energy (kWh) using the industry standard approach. This is why two homes with the same volume used can show slightly different kWh if the calorific value differs.

  1. Work out gas used (volume). Subtract the previous reading from the latest reading.
  2. If your meter is imperial (ft³), convert to m³. Multiply the volume used by 0.0283.
  3. Apply the correction factor. This adjusts for temperature and pressure. Bills commonly show 1.02264.
  4. Multiply by the calorific value (CV). This is the energy content of the gas, shown on your bill (often around 39–41 MJ/m³).
  5. Divide by 3.6 to convert from megajoules to kWh.

Formula

kWh = volume used (m³) × 1.02264 × calorific value (MJ/m³) ÷ 3.6

If your meter is in ft³: kWh = (volume used (ft³) × 0.0283) × 1.02264 × CV ÷ 3.6

Tip: Your bill may show the conversion already (sometimes labelled “units”, “volume”, “correction”, “calorific value”). Using the same numbers from your bill is the best way to match your supplier’s kWh.

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Worked examples (with realistic numbers)

These examples show the maths end-to-end so you can sanity-check a bill. We’ve used common UK values for correction factor and calorific value; your bill may differ.

Scenario 1: Metric meter (m³)

Volume used
35.0 m³
Correction factor
1.02264
Calorific value
39.2 MJ/m³

kWh = 35.0 × 1.02264 × 39.2 ÷ 3.6

kWh ≈ 390.0 kWh (rounded)

If your unit rate is, say, 6.5p/kWh, the usage charge would be about £25.35 before standing charge and VAT.

Scenario 2: Imperial meter (ft³)

Volume used
120 ft³
Convert to m³
120 × 0.0283 = 3.396 m³
Correction factor
1.02264
Calorific value
40.0 MJ/m³

kWh = 3.396 × 1.02264 × 40.0 ÷ 3.6

kWh ≈ 38.6 kWh (rounded)

Common mismatch: many people forget the ft³ → m³ step, which can make your estimate ~35x too high or low depending on the direction of the mistake.

If your bill still doesn’t match: check whether the supplier has used a different calorific value for different days, or whether your readings were estimated. Small differences can also come from rounding and billing periods.

Metric vs imperial gas meters (what to do)

Your meter type affects whether you need the extra conversion step. If you’re unsure, the meter face usually shows m³ or ft³.

Meter type What you’ll see Extra step needed? What to do
Metric m³ on the meter No Use volume in m³ directly in the kWh formula.
Imperial ft³ on the meter (often older meters) Yes Convert ft³ to m³ (× 0.0283), then apply the kWh formula.
Smart meter May show kWh on in-home display; supplier still bills in kWh Usually no (for the user) Use the bill’s kWh to compare tariffs; use the formula if you’re auditing readings.

When converting helps

  • Checking a new bill after a price change or tariff switch
  • Spotting whether estimated readings are inflating your charges
  • Understanding how much gas you use in kWh for comparisons

When it may not be worth it

  • If your bill already shows the kWh clearly and readings are accurate
  • If you’re using this to predict exact costs (CV changes and rounding apply)
  • If your issue is likely standing charges, discounts or debt repayment

Reminder: Your total bill is typically (kWh × unit rate) + (days × standing charge), plus VAT. Even if kWh is correct, standing charges can still make bills feel higher.

Costs, exclusions and common pitfalls (UK)

Conversion is straightforward, but these are the usual reasons people get different numbers from their supplier — or misunderstand what kWh means for their costs.

1) Using a generic calorific value

CV changes slightly by time and network area. For the closest match, use the exact CV printed on your bill for that period.

2) Mixing up m³ and ft³

Imperial meters need the ft³ × 0.0283 step before the main formula. This is the biggest source of major errors.

3) Rounding differences

Suppliers may round volume, CV and final kWh at different steps. Expect small variations (often a few decimal places).

4) Estimated readings

If a reading is estimated, your kWh might look “wrong” because the input data is wrong. Submitting a new reading can correct this.

5) Standing charge and billing days

Even with low usage, bills can be higher than expected due to standing charge × number of days in the period.

6) Payment method differences

Direct Debit, prepayment and credit tariffs can differ. Unit rate and standing charge vary by tariff and region (and can change at different times).

If you think your gas bill is wrong

  • Check the reading on your meter matches the reading on the bill (and the correct units: m³ vs ft³).
  • Confirm the bill uses actual readings, not estimated.
  • Recalculate kWh using the bill’s CV and correction factor.
  • If it still looks off, contact your supplier and keep a record of readings and dates. Citizens Advice has practical guidance on billing issues.

External help: Citizens Advice energy supply guidance

FAQs

Why does my gas bill show kWh when my meter shows m³ or ft³?

Your meter measures gas volume, but suppliers bill for energy used (kWh). The volume is converted using a correction factor and calorific value so the bill reflects the energy content of the gas supplied.

What is the correction factor 1.02264 on UK gas bills?

It’s an industry standard factor used to account for temperature and pressure so volume can be converted into an equivalent energy figure. Many UK bills use 1.02264, but use the value shown on your statement if it differs.

Where do I find the calorific value to convert gas to kWh?

It’s usually printed on your gas bill near the usage calculation and may be labelled “calorific value” or “CV”. It can vary slightly by day and location, so using the bill’s CV is the best way to match the supplier’s kWh.

How do I convert an imperial gas meter reading (ft³) to kWh?

First convert ft³ to m³ by multiplying by 0.0283. Then use: kWh = m³ × 1.02264 × calorific value ÷ 3.6. Small differences from your bill can happen due to rounding or a different calorific value.

Why doesn’t my calculation exactly match my supplier’s kWh?

The most common reasons are: you used a different calorific value, the supplier applied multiple CVs across the billing period, readings were estimated, or rounding was applied at different steps. Using the exact values printed on your bill usually gives the closest match.

Does converting gas units to kWh help me compare tariffs?

Yes. Tariffs are priced per kWh plus a standing charge, so understanding your kWh usage helps you compare unit rates more meaningfully. But total cost still depends on standing charges, billing days, and whether you’re on credit, Direct Debit or prepayment.

Can I use kWh to estimate my monthly gas cost?

You can estimate by multiplying expected kWh by your unit rate and adding the standing charge for the number of days. Treat it as an estimate: weather, heating habits, tariff changes, and bill rounding can all affect the final amount.

Is the gas kWh conversion the same across the UK?

The method is the same, but your calorific value can vary slightly by location and over time, and unit rates/standing charges vary by region and supplier. Always use the figures on your bill for the most accurate conversion for your address.

Trust, methodology and sources

Page details

Last updated
July 2026

How we assess this (and limitations)

  • Method: We explain the standard UK bill conversion: volume → corrected volume → energy (kWh) using correction factor, calorific value and MJ-to-kWh conversion.
  • Assumptions in examples: Correction factor 1.02264; calorific value around 39–40 MJ/m³; rounding to one decimal place for readability.
  • Limitations: Suppliers may apply different calorific values across a billing period and round at different stages; smart meter/IHD displays may not match bill timing; tariff costs also depend on standing charges, VAT and any credits/debits.
  • What we do not do: We do not estimate your personal bill total without your tariff rates and billing dates.

Sources (UK)

We link to general UK guidance pages; suppliers may present calculations differently on statements.

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Updated on 2 Jul 2026