Calculator help

Help using Gas Bill Calculator

Where to find each figure, what to enter and what to check when a result does not look right.

1. Choose the meter type

Select metric if the meter is marked m³. Select imperial if it is marked ft³ or cubic feet. Choosing the wrong one makes a large difference because imperial units need an extra conversion.

See photos and instructions for each meter type →

2. Enter two readings

Use an earlier reading and a later, higher reading. Enter the main whole-number digits only; ignore red digits and anything after the decimal point. The readings can come from the meter or from two bills, provided they cover the same meter.

Example entries: previous reading 12345, current reading 12380. Select metric for a meter marked m³. That is 35 metric units used.

3. Enter your tariff

Look for the gas unit rate in pence per kWh and the gas standing charge in pence per day. Use the number of days between the two readings, not necessarily the number of days in a calendar month.

VAT check: the calculator adds 5% VAT. Enter rates before VAT if your bill lists VAT separately. If the rates already include VAT, divide them by 1.05 before entering them.

For example, a VAT-inclusive rate of 7.35p per kWh becomes 7.00p before VAT: 7.35 ÷ 1.05 = 7.00. Apply the same conversion to a VAT-inclusive standing charge.

Advanced conversion factors

Most people should leave these alone. The volume correction adjusts gas volume for temperature and pressure. The calorific value is the energy contained in the gas and is normally printed on the bill. The imperial factor converts hundreds of cubic feet to cubic metres.

Understanding the result

The result shows the converted kWh, cost of gas used, standing charge and VAT. Monthly or annual projections simply scale the daily usage in your selected period; a short winter period will usually produce an unrealistically high annual projection.

Common problems

“Current reading must be higher”: Check that the older reading is first. If a meter has rolled over to zero, the calculator cannot currently handle that reading pair.
The result is far too high: Check the meter type and make sure you did not include decimal or red digits. Also check that prices are entered in pence, not pounds.
It does not match the supplier bill: Check dates, tariff changes, estimated readings, the calorific value and whether VAT has been counted twice.

Open the calculator

See the full calculation. If the website itself is not working, report a problem.