Your gas meter measures the amount of gas you use. However, your supplier charges you in kilowatt-hours (kWh). So, your meter reading must first be converted into kWh.
Why Is Gas Different?
Electricity meters usually measure energy use directly in kWh.
Gas meters work differently. Instead, they measure the volume of gas you use.
Most newer gas meters measure this in cubic metres (m³). However, some older meters measure gas in cubic feet.
So, there are a few extra steps before you can work out the cost.
Start With Your Readings
First, take your current gas meter reading.
Then, subtract your previous reading.
For example:
Current reading: 8,450
Previous reading: 8,350
So:
8,450 − 8,350 = 100 m³
You have used 100 cubic metres of gas.
However, this is not 100 kWh.
You now need to convert the gas into kWh.
Check Your Meter Type
Before you calculate anything, check whether your meter is metric or imperial.
A metric meter measures gas in:
Cubic metres (m³)
An imperial meter measures gas in:
Cubic feet (ft³)
The unit should be shown on your meter. Also, you can check your energy bill.
If you have an imperial meter, you need one extra step.
Imperial Gas Meters
If your meter measures gas in hundreds of cubic feet, first multiply the amount used by 2.83.
For example:
35 × 2.83 = 99.05 m³
You can then continue with the normal calculation.
If your meter already measures gas in cubic metres, you can skip this step.
Convert Gas to kWh
For a metric meter, use this formula:
Gas used (m³) × 1.02264 × calorific value ÷ 3.6 = kWh
The 1.02264 figure adjusts the gas volume for temperature and pressure.
The calorific value tells you how much energy the gas contains.
This value can change. So, for the most accurate result, use the figure shown on your bill.
Worked Example
Suppose you used:
100 m³ of gas
and the calorific value on your bill is:
39.5
The calculation is:
100 × 1.02264 × 39.5 ÷ 3.6
This gives about:
1,122 kWh
So, 100 m³ of gas in this example contains about 1,122 kWh of energy.
Work Out the Cost
Once you know the kWh, the rest is much simpler.
Suppose your gas unit rate is:
6.5p per kWh
Then:
1,122 × £0.065 = £72.93
So, the gas you used costs about £72.93.
However, this is not the full cost because you may also pay a standing charge.
Add the Standing Charge
Suppose your standing charge is:
32p per day
and the bill covers:
30 days
Then:
30 × £0.32 = £9.60
Now add this to the cost of the gas:
£72.93 + £9.60 = £82.53
So, the estimated gas cost is £82.53.
These figures are examples only.
The Full Calculation
The whole process is:
Meter readings → Gas used → kWh → Unit rate → Cost
For a metric meter:
Current reading − Previous reading
Then:
Gas used × 1.02264 × calorific value ÷ 3.6 = kWh
Then:
kWh × unit rate = gas use cost
Finally:
Gas use cost + standing charges = estimated gas cost
Why Doesn’t My Bill Match?
Your gas meter measures volume, while your bill shows energy in kWh.
So, the number of kWh on your bill will not normally match the change in your meter reading.
For example, using 100 m³ of gas could equal well over 1,000 kWh.
Therefore, a much larger kWh figure on your bill does not by itself mean something is wrong.
A Quick Estimate
If you only need a rough figure, 1 m³ of natural gas is often around 11 kWh.
So:
50 m³ × 11 ≈ 550 kWh
However, this is only a quick estimate.
If you are checking a bill, use the full calculation and the calorific value shown on that bill.
What Do You Need?
To check your gas cost, find:
- your previous meter reading
- your current meter reading
- your meter type
- the calorific value
- your gas unit rate
- your standing charge
- the number of days covered
Most of this information should be on your bill.
Key Points
Your gas meter measures gas volume. However, you pay for gas in kWh.
So, the meter reading must first be converted.
Metric and imperial meters need slightly different calculations.
Also, the calorific value can change. Therefore, use the figure on your bill when you want a more accurate result.
Finally, add your standing charge to the cost of the gas you used.
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