Free gas bill check

Gas units to kWh calculator

Turn m³ or imperial gas readings into kWh, price the gas used and compare it with the kWh on your bill. The unit selector distinguishes hundreds of cubic feet from actual cubic feet, which prevents a hundredfold conversion mistake.

Reviewed 8 October 2026 · BillDecoded editorial team · Formulas and testing

Convert your gas volume and check the charge

Use the units and calorific value printed on the same bill. Enter prices including any applicable VAT; the tool does not add VAT again. Calculator inputs stay in your browser.

What do you have?

Unit of that volume or reading difference

Gas volume used

A traditional imperial meter’s main reading is normally in hundreds of cubic feet. Actual ft³ is a separate option for a volume explicitly stated that way. Do not treat an electricity kWh reading as gas volume.

Calorific value on the bill (MJ/m³)

Volume correction factor on the bill

Gas unit rate including VAT (p/kWh)

Gas standing charge including VAT (p/day)

Billed days

Gas kWh shown on bill (optional)

The price defaults are dated October–December 2026 GB direct-debit averages. The 39.5 calorific value is an illustration; replace it with the value from your bill. Enter zero standing charge when checking usage cost alone.

Calculated gas kWh

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Usage cost

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Standing charge

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Gas charge subtotal

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Billed kWh minus calculation

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Enter a gas volume or two readings to calculate.

Which gas unit should you choose?

What the figure means	Choose	Conversion to m³
A metric meter marked m³ or a billed metric volume	Cubic metres	Volume × 1
The difference between the main readings of a traditional imperial meter	Hundreds of cubic feet	Reading difference × 2.83
A volume explicitly given in individual cubic feet	Actual cubic feet	Volume × 0.0283

Read the meter unit and the bill’s conversion line together. Do not choose a factor only because the meter label says ft³. A replaced meter, rollover or different register cannot be checked by simply subtracting the two readings; use separate periods and the supplier’s exchange readings.

The GOV.UK gas-bill calculation guide sets out the distinction between individual cubic feet and the hundreds of cubic feet used for imperial meter readings.

Worked example: 100 m³ of gas over 30 days

This is BillDecoded’s own arithmetic using an illustrative calorific value of 39.5, correction factor 1.02264 and dated October–December 2026 average gas prices of 7.97p/kWh plus 29.68p/day.

Line	Calculation	Result
Gas energy	100 × 1.02264 × 39.5 ÷ 3.6	1,122.063 kWh
Usage charge	1,122.063333… × 7.97 ÷ 100	£89.43
Standing charge	30 × 29.68 ÷ 100	£8.90
Subtotal	Unrounded usage + standing charge	£98.33

If the bill instead reports 1,200 kWh for exactly these readings and factors, the difference is 77.937 kWh, equivalent to about £6.21 in usage cost at that example rate. That is a calculation to reconcile, not proof of a supplier error or a refund entitlement.

If the bill’s kWh does not match

Match the opening date, closing date and whether readings are actual or estimated.
Check the meter serial number and whether the supplier has recorded a metric or imperial meter.
Use the calorific value and volume correction factor printed for the billed period.
Ask whether the supplier rounded or split the readings, rates or conversion lines.
Compare usage charges separately from account credit, debt, discounts and payments.

If the supplier has applied the imperial 2.83 volume factor to a metric reading, the calculated kWh will be 2.83 times the metric calculation when all other factors match. Check the bill’s actual conversion line before alleging this mistake.

Request a gas-conversion breakdown

Please explain the gas kWh calculation for [bill dates]. My opening and closing readings are [readings], from meter [serial number] marked [m³ / imperial]. Please confirm the volume units, metric conversion, calorific value, correction factor and any rounding used. My calculation gives [kWh], compared with [billed kWh] on the statement. I have attached dated readings and the calculation. Please reconcile the difference and issue a corrected bill if an error is confirmed.

Full wrong-reading complaint template · Meter identity check · Complaint timing.

Use the right tool for the bill

Already have gas kWh? Use the kWh cost calculator without converting it again.
Rate changes during the bill? Convert each reading segment, then use the split-period bill calculator.
Electricity meter readings? Use the bill-from-readings calculator; electricity registers already measure kWh.
A payment increase? After checking the charge, review the monthly direct debit.

Frequently asked questions

Is one gas unit one kWh?

No. Gas meters measure volume. A metric m³ and an imperial meter unit representing 100 ft³ convert to different kWh totals; the bill’s calorific value also affects the result.

Should I multiply cubic feet by 2.83?

Use 2.83 for hundreds of cubic feet, such as the main imperial meter reading difference. For individual cubic feet, the factor is 0.0283. Choose the unit actually represented by the number.

Which calorific value should I enter?

Enter the calorific value printed on the bill for the same period. The 39.5 default is an example, not a value guaranteed for your supply.

Does a difference prove I was overcharged?

No. First reconcile the period, reading type, volume units, conversion values, rates and rounding with the supplier. The tool checks arithmetic and cannot decide liability.

Sources and limits

This tool holds one unit rate and one daily standing charge constant. It does not reproduce a supplier’s billing system, predict future tariffs or cover LPG, heat-network bills, meter replacements or multi-tier tariffs. Currency is rounded for display; intermediate arithmetic remains unrounded. Use your own tariff outside the GB cap reference, including Northern Ireland.

Information and arithmetic checks only. BillDecoded is independent of suppliers and regulators.