How to calculate a gas bill from meter readings

1. Find the gas used

Subtract your previous reading from your current reading. For example, 12,380 − 12,345 = 35 metric units.

2. Convert the units to kWh

For a metric meter, use the volume correction and calorific value printed on the bill:

For an imperial meter, first multiply the units by 2.83 to convert hundreds of cubic feet to cubic metres.

3. Apply the unit rate

If the rate before VAT is 6.98p per kWh:

4. Add the standing charge

For 30 days at 27.66p a day, the standing charge is £8.30. Add that to the usage charge: £27.24 + £8.30 = £35.54.

5. Add VAT if needed

If the rates you used exclude VAT, add 5%. Keeping the charges at full precision until the final rounding gives £37.31. Rounding the subtotal to £35.54 first would give £37.32; this calculator rounds the final total instead. Do not add VAT twice if your rates already include it.

Why your supplier’s figure can differ

Small differences can come from rounding, the exact calorific value, an imperial conversion, a price change part-way through the bill or a tariff discount. Compare the calculation period and whether rates include VAT before assuming either total is wrong.

Worked example for an imperial gas meter

Readings of 1,234 and 1,244 give 10 imperial units. Each unit represents 100 cubic feet, so multiply by 2.83 before applying the other conversion factors:

At an illustrative 6.98p per kWh before VAT, usage costs £22.02. For 30 days at 27.66p per day before VAT, standing charges are £8.30. Including 5% VAT gives approximately £31.84.

Both examples use illustrative tariffs, not a recommended or guaranteed rate. The calculator rounds kWh to two decimal places, calculates charges at full precision and rounds displayed money to pennies. Displayed intermediate values can therefore differ slightly from the final total.

Method: Government guidance on gas bill calculation. Need help identifying the units? See gas meter types and the conversion terms.