How to convert a gas meter reading to kWh (UK)
Work out the kWh your gas use represents for your bill, a smart meter check, or to compare tariffs. We’ll show the exact UK formula, how it differs for metric vs imperial meters, and two realistic worked examples.
- Includes metric (m³) and imperial (ft³) meter steps
- Explains calorific value, correction factor and unit rates
- Common pitfalls that cause “my bill looks wrong” moments
Figures are estimates. Your bill uses your supplier’s calorific value and billing period dates.
Fast answer: how to convert gas meter reading to kWh
To convert gas meter reading to kWh, take the units used (m³ or ft³), multiply by 1.02264, multiply by the calorific value (typically ~39–40 MJ/m³), then divide by 3.6. If your meter is in ft³ (imperial), multiply the units by 2.83 first to convert to m³.
Most important detail: the calorific value and the exact dates on your bill can slightly change the final kWh.
Key takeaways
- Metric meter: kWh = m³ × 1.02264 × calorific value ÷ 3.6
- Imperial meter: kWh = ft³ × 2.83 × 1.02264 × calorific value ÷ 3.6
- Only use the black digits (ignore red digits/decimals) unless your supplier states otherwise.
- Your bill’s kWh may differ slightly due to rounding and average calorific value.
Step-by-step: convert your gas units to kWh
You need two meter readings (start and end) and the calorific value used for billing. You’ll find calorific value on your gas bill (often shown as “CV”). If you can’t find it, use an estimate (we show a typical range below).
1) Work out units used
Units used = latest reading − previous reading. Use the black numbers only (ignore red digits and digits after a decimal point).
2) Identify meter type: metric (m³) or imperial (ft³)
If the meter shows m³, it’s metric. If it shows ft³ or “cubic feet”, it’s imperial (older style).
3) Convert to kWh using the UK billing formula
Metric (m³): kWh = units × 1.02264 × calorific value ÷ 3.6
Imperial (ft³): kWh = units × 2.83 × 1.02264 × calorific value ÷ 3.6
Why those numbers? 1.02264 is the volume correction factor. 3.6 converts megajoules to kWh. 2.83 converts cubic feet to cubic metres.
4) Estimate your gas cost (optional)
Estimated cost = (kWh × unit rate) + standing charges for the days in the period. Unit rate and standing charge are on your tariff/bill. VAT is usually included on domestic bills; check your breakdown.
Typical calorific value (CV) in the UK
Many suppliers use a CV around 39.0 to 40.0 MJ/m³ (often shown to 1–3 decimal places). Always use the CV printed on your bill for the closest match.
Get a whole-of-market quote (and check your tariff)
If you’re converting readings to understand your bill or compare unit rates, we can help you compare options across the market. No promises—availability and prices vary by postcode, meter type and payment method.
Two worked examples (realistic UK scenarios)
Example 1: Metric meter (m³)
Assumptions: Previous reading 01234, latest reading 01274 → 40 m³ used. Calorific value 39.4. Correction factor 1.02264.
kWh = 40 × 1.02264 × 39.4 ÷ 3.6 = ≈ 447.2 kWh
If your unit rate were 6.5p/kWh, usage cost would be roughly £29.07 (447.2 × £0.065), plus standing charges for the period.
Example 2: Imperial meter (ft³)
Assumptions: Previous reading 53210, latest reading 53310 → 100 ft³ used. Calorific value 39.2.
kWh = 100 × 2.83 × 1.02264 × 39.2 ÷ 3.6 = ≈ 315.0 kWh
Imperial conversions often surprise people because the “units” look smaller/larger than kWh. The formula bridges that gap.
If your result doesn’t match your bill exactly
- Your supplier may use a slightly different CV (often averages across the billing period).
- Your bill may split usage across price changes or different dates.
- Rounding can occur at multiple steps (meter read, kWh, pence).
Metric vs imperial: what changes in the calculation?
| What you see on the meter | Meter type | Extra step before kWh | kWh formula (summary) |
|---|---|---|---|
| m³ | Metric | None | m³ × 1.02264 × CV ÷ 3.6 |
| ft³ / cubic feet | Imperial | Convert ft³ to m³ (× 2.83) | ft³ × 2.83 × 1.02264 × CV ÷ 3.6 |
Decision checklist: when converting to kWh helps
- You want to sanity-check a bill after a meter reading or move-in.
- You’re comparing tariffs and need your consumption in kWh.
- You have an imperial meter and your “units” don’t look like kWh.
- You’re tracking usage manually between smart meter updates.
When a simple conversion may not match your bill
- Your bill spans a price change (two unit rates in one period).
- Your supplier used estimated reads or later corrected them.
- You’re on prepayment (top-ups vs billing periods can differ).
- You have a smart meter but the in-home display shows costs using tariff data that’s out of date.
Common pitfalls (and how to avoid them)
Including the red digits
Most UK gas meters have red digits (or digits after a decimal) for extra precision. For billing reads, you usually submit black digits only. Including red digits can inflate usage.
Using the wrong meter type
If your meter is imperial (ft³) but you use the metric formula, your kWh will be way off. Check for m³ vs ft³ on the meter face.
Calorific value mismatch
CV varies slightly by location and over time. If you use a generic CV instead of the one on your bill, expect a small difference.
Billing period vs calendar month
Standing charges are charged per day. If you’re checking a bill, use the exact number of days on the statement (not “roughly a month”).
Estimated reads and corrections
If your supplier estimated a read, the kWh figure can be corrected later when an actual read is received. This can make one bill look unusually high/low.
Comparing tariffs using £ only
To compare tariffs fairly, use kWh (consumption) and include standing charges. Two tariffs can have similar unit rates but very different standing charges.
If you think your bill is wrong: start by checking the readings and meter type, then check the bill’s CV and dates. If it still doesn’t add up, contact your supplier and ask them to explain the calculation (and whether the bill includes estimated reads).
FAQs
- What is the formula to convert gas to kWh in the UK?
- UK suppliers typically use: kWh = units × correction factor (1.02264) × calorific value ÷ 3.6. If your meter measures in cubic feet (imperial), convert to cubic metres first by multiplying units by 2.83.
- How do I know if my gas meter is metric or imperial?
- Look at the unit printed on the meter: m³ means metric, while ft³ (or “cubic feet”) means imperial. Imperial meters are often older with a mechanical dial display, but the printed unit is the reliable check.
- Do I include the red numbers when taking a gas meter reading?
- Usually, no. For most UK meters you submit the black digits only and ignore red digits and any numbers after a decimal point. If your supplier wants decimals (rare), they’ll say so on your bill or in your online account instructions.
- Why doesn’t my kWh calculation match my gas bill exactly?
- Small differences are common because bills can use an average calorific value over the billing period, apply rounding, split usage across tariff changes, or correct earlier estimated readings. Using the CV and exact dates shown on your bill will usually get you closest.
- What calorific value should I use for a quick estimate?
- If you can’t see CV on your bill, a reasonable UK estimate is around 39.0–40.0 MJ/m³. For a close match to your statement, use the CV shown on your bill, as it can vary slightly by region and over time.
- Does this conversion work for smart meters and prepayment meters?
- Yes—the underlying conversion from volume to kWh is the same. What can differ is how readings are collected (automatic vs manual) and how charges appear (top-ups and standing charges on prepayment). Always check the dates and whether any reads were estimated.
- Can I use kWh from my bill to compare energy tariffs?
- Yes. The kWh figure on your bill is the best starting point for comparisons because it already reflects the supplier’s conversion factors. For the most accurate comparison, use annual usage (kWh per year) and include standing charges, payment method, and any fixed-term exit fees.
- What should I do if my meter reading seems to have gone backwards or jumped?
- If a reading looks wrong, re-check you’re reading the correct meter (gas vs electric), using black digits only, and reading left-to-right. If it still looks incorrect, contact your supplier promptly—billing errors can happen after meter exchanges, incorrect account details, or misreads.
Trust, methodology and sources
How we assess this (and limitations)
- Formula: We use the standard UK billing approach: volume used × correction factor × calorific value ÷ 3.6, with an additional ft³→m³ conversion for imperial meters.
- Correction factor: We reference the commonly used 1.02264 value shown on UK bills. Suppliers may display it rounded.
- Calorific value: Our examples use realistic CV values (around 39–40 MJ/m³). Your supplier’s CV can differ by region and day, and bills may use period averages.
- Rounding: Bills may round at several stages (reads, kWh, pence). Our example outputs are therefore approximate.
- Tariff costs: Any cost figures shown are illustrative and exclude factors like tiered prices, discounts, debt repayments or changes during the billing period.
Helpful UK sources
- Ofgem: checking your energy bill
- Citizens Advice: check your energy bill
- GOV.UK: smart meters guidance
EnergyPlus is a whole-of-market comparison service for UK homes. We aim to explain calculations clearly so you can sense-check your bills and compare tariffs with confidence.
Ready to compare energy prices using your kWh?
Use your bill’s kWh (or the conversion above) to compare tariffs more accurately. Results depend on your postcode, meter type, and payment method.
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