We think it’s important you know how we work out the prices you pay for your energy, so we've put together this article to help explain how we calculate your gas usage.

Your meter records how many gas units you’ve used, and works out how much you owe. It does this by calculating the amount of units you’ve used in Kilowatt Hours (kWhs) against the price of gas you pay.

What you need to work it out

Your meter automatically does this for you, but if you’d like to work it out, it’s easy to do. You’ll need:

  • Two meter readings (taken on different days)
  • The calorific value and the correction factor (we’ll tell you more about this below!)
  • Your meter type
  • The amount you pay for each kWh of gas you use

You can find this information on your meter. On the front, it’ll show if you have an imperial meter (it’ll have the letters ‘ft3’ on it) or a metric meter (it’ll have ‘m3’ instead). You can get all the other information by cycling through the different display screens on your meter (there’ll be a little button on the front to do this).

How to work it out

1. Take away your last reading from your current reading.

This is how many units you’ve used.

2. If you’ve got a metric meter (m3), you can ignore this step. If you’ve got an imperial meter (ft3), we need to convert your units from cubic feet to cubic metres.

To do this, we multiply the units you’ve used by 2.83.

3. Multiply this number by the calorific value.

A typical value example is 39.2.

4. Multiply this number by 1.02264.

This is the correction factor.

5. Divide this number by 3.6.

This converts it to kWh.

6. Multiply this number by the price-per-kWh.

You might have a daily standing charge or a set price for an initial amount of units used, then a lower price for any extra units used after this.

What is the calorific value?

The calorific value is the amount of energy which gets released when gas is burned. It’s measured regularly by the National Grid and it’s the same for all suppliers. A typical example is 39.2, but you can see the current value by cycling through the display screens on your meter.

What is the correction factor?

The correction factor converts gas units into kWh by working out the volume of gas based on temperature and pressure. It can vary slightly, but all suppliers use a standard factor of 1.02264. This makes sure we all get the same number of kWh for each cubic metre of gas.

If something doesn’t seem quite right

Don’t worry, just get in touch and we’ll be happy to help.