How to convert gas m3 to kWh (UK bill guide)

Learn the UK gas meter conversion from cubic metres (m³) to kilowatt hours (kWh), why your bill uses kWh, and how to check your supplier’s maths using the official formula.

  • Fast, step-by-step formula (with a worked example)
  • What “calorific value” and “correction factor” mean in plain English
  • Common UK pitfalls: metric vs imperial meters, smart meters, estimates
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Figures are illustrative. Your bill’s calorific value (CV) and billing period dates affect the exact kWh.

Fast answer: how to convert gas m3 to kWh

To convert gas m3 to kWh, multiply the volume used in m³ by 1.02264, then multiply by the calorific value (CV) shown on your bill, and divide by 3.6. In most UK bills this works out to roughly 11 kWh per m³, but your exact figure depends on your CV and billing period.

Official UK formula (metric meters)

kWh = m³ used × 1.02264 × CV ÷ 3.6

Your bill may show CV around 39–41 MJ/m³. Suppliers use a CV set for your area and time period.

Key takeaways (UK)

  • Suppliers bill in kWh so you can compare energy fairly (it’s the energy content, not the volume).
  • m³ vs ft³ matters: imperial meters need an extra step (× 2.83 to convert ft³ to m³).
  • Small differences are normal due to rounding, billing dates, and CV changes.
  • Always use the CV printed on your bill when checking a specific statement.

m³ to kWh: step-by-step (and what the numbers mean)

If your gas meter is metric, it measures in cubic metres (m³). Your supplier converts that volume into kWh using a standard UK approach so you’re billed for the energy content of the gas.

  1. Find your usage in m³: current meter reading minus previous reading (make sure both are actual readings where possible).
  2. Apply the correction factor (1.02264): adjusts for temperature and pressure.
  3. Multiply by calorific value (CV): the energy in the gas (shown on your bill, often around 39–41 MJ/m³).
  4. Divide by 3.6: converts megajoules into kilowatt hours (1 kWh = 3.6 MJ).
Quick sense-check: many UK households see around 10.5–11.5 kWh per 1 m³. If you’re far outside that, double-check whether your meter is imperial (ft³), whether the reading included decimals, and whether the billing period spans a CV change.

Why your CV can differ from a friend’s

Gas quality varies by network and time. The CV on your bill typically reflects the average CV for your Local Distribution Zone (LDZ) over the billing period. That’s why two homes with the same m³ usage can show slightly different kWh.

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What you need from your bill

  • Your meter unit: m³ (metric) or ft³ (imperial)
  • Your calorific value (CV) (sometimes called “cal value”)
  • The readings and dates for that statement

Worked examples (realistic UK scenarios)

These examples show the same approach your supplier uses. We’ve stated the assumptions so you can swap in your own numbers from your bill.

Scenario 1: metric meter (m³)

Gas used
45 m³
Correction factor
1.02264
Calorific value (CV)
39.5 MJ/m³

kWh = 45 × 1.02264 × 39.5 ÷ 3.6

Result (estimated): 504.9 kWh (often rounded on bills)

Assumption: CV stays at 39.5 across the billing period (some bills use an average across dates).

Scenario 2: imperial meter (ft³)

Gas used
100 ft³
Convert to m³
÷ 2.83
Correction factor
1.02264
Calorific value (CV)
40.2 MJ/m³

kWh = (100 ÷ 2.83) × 1.02264 × 40.2 ÷ 3.6

Result (estimated): 410.1 kWh

Assumption: 2.83 is used as the ft³→m³ conversion (suppliers may show more decimal places).

Why your bill might not match exactly: suppliers can round intermediate steps, apply CV averages across multiple dates, and show kWh to fewer decimal places than the calculation uses.

m³ vs ft³ (imperial): which meter do you have?

The conversion is different depending on whether your meter is metric (m³) or imperial (ft³). This table helps you identify your meter and choose the right calculation.

What you see on the meter Unit type What to do Common mistake
Labelled m³ or shows “cubic metres” Metric Use: m³ × 1.02264 × CV ÷ 3.6 Treating it as ft³ and dividing by 2.83
Labelled ft³ or “cubic feet” Imperial First convert: ft³ ÷ 2.83 = m³, then apply the metric formula Skipping ft³→m³ conversion (kWh ends up too high)
Smart meter / in-home display shows kWh Already converted Use the kWh figure for budgeting and tariff comparisons Trying to convert again (double-counting)

Decision checklist: who this guide is for

  • You’re comparing gas tariffs and want to use kWh properly.
  • Your statement shows readings in m³ and billed usage in kWh.
  • You suspect your bill is estimated and want to validate the conversion.

Who it may not suit (or needs extra care)

  • You have an imperial meter and aren’t sure about ft³ vs m³ (check the label first).
  • Your bill spans multiple CV values or shows multiple “gas units” lines.
  • You’re on prepayment: the display may show kWh or £, not m³—your supplier’s statement is the best reference.

Common UK pitfalls (and how to avoid them)

1) Mixing up metric and imperial

If your meter is in ft³ and you treat it as m³, your kWh will be far too high. Check the unit printed on the meter face.

2) Reading the wrong digits

Some meters have red digits or decimals. Many suppliers ask you to submit only the black digits. If you include decimals when you shouldn’t, usage can look wildly wrong.

3) CV changes across the bill

Long billing periods can cover multiple CV averages. If your bill lists more than one CV, use the bill’s breakdown rather than a single “average” you found online.

4) Estimated readings and catch-up bills

If one bill is estimated and the next is actual, the “actual” bill can look unusually high or low because it corrects earlier estimates. The conversion may be fine even when the usage pattern looks odd.

5) Unit rate vs standing charge confusion

You’re billed for kWh used (unit rate) plus a daily standing charge. Converting m³ to kWh won’t include standing charges—so it won’t match the total bill on its own.

6) Regional & payment method differences

Tariff prices can differ by region and payment method (direct debit, cash/cheque, prepayment). Converting usage to kWh helps comparison, but your actual price depends on tariff terms and eligibility.

If you think your bill is wrong: first take an up-to-date meter reading and compare it with your last statement. If the readings are correct but the conversion looks off, ask your supplier to explain the CV and correction factor used for your billing dates.

FAQs

What is the standard formula to convert gas m3 to kWh in the UK?

For a metric (m³) meter: kWh = m³ × 1.02264 × CV ÷ 3.6. Your supplier prints the calorific value (CV) on your bill and uses it for the billing period.

Why do UK gas bills use kWh instead of m3?

Because kWh measures energy, not volume. The energy you get from a cubic metre can vary slightly with gas composition and conditions, so converting to kWh allows fairer billing and easier tariff comparison.

What’s a typical kWh per 1 m3 of gas in the UK?

A common rough guide is around 11 kWh per 1 m³, but it varies with your bill’s CV and rounding. For checking a specific bill, always use the exact CV shown on that statement.

How do I convert gas ft3 to kWh if my meter is imperial?

Convert cubic feet to cubic metres first: m³ = ft³ ÷ 2.83. Then use the metric formula: kWh = m³ × 1.02264 × CV ÷ 3.6. Your bill may show a more precise conversion factor.

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

Small differences are common due to rounding, bills spanning multiple CV averages, and suppliers rounding at different stages. If the difference is large, double-check meter units (m³ vs ft³) and whether you included decimals you shouldn’t.

Does the conversion affect how much I pay for gas?

The conversion itself doesn’t change your price—it’s how usage is measured. What you pay depends on your kWh used multiplied by your unit rate, plus your standing charge, and any tariff terms (for example, fixed-term exit fees may apply).

Where can I find the calorific value (CV) on my UK gas bill?

It’s usually listed in the “how we calculated your gas usage” section, often labelled calorific value, CV or cal value. Some bills show a single CV for the period; others show an average or multiple lines.

If I’m on a smart meter or prepayment meter, do I still need to convert m3 to kWh?

Often no—many smart and prepayment displays show kWh or cost. However, your supplier statement may still reference meter readings and the conversion. If your meter shows m³, the same formula applies.

Trust, methodology and sources

Page ownership

Last updated
July 2026

How we assess this (and limitations)

  • Formula: We use the standard UK supplier approach for converting gas volume to kWh (including correction factor 1.02264, CV in MJ/m³, and ÷ 3.6).
  • Examples: Our scenarios use realistic CV values (around 39–41) and show rounding as “estimated”.
  • Limitations: Your supplier may apply CV averages over multiple dates and round at different steps, so your manual calculation may differ slightly.
  • Not financial advice: This page explains conversion, not what tariff you should pick. Tariff eligibility, regional rates and exit fees vary by supplier.

Sources (UK)

We link to official and consumer guidance so you can cross-check terminology and billing rights.

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Updated on 2 Jul 2026