In the UK, energy is priced per kilowatt-hour (kWh). However, your gas meter might record your consumption by volume, in cubic metres (m³) or cubic feet (ft³).
Therefore, when doing a meter reading to submit to your energy supplier, you may need to convert the reading from volume into kWh. Knowing how many kilowatt-hours of gas you’ve consumed allows your supplier to bill you accurately.
You only have to worry about doing the conversion and submitting the readings to your supplier if you have an older gas meter. Next-generation smart meters, currently being rolled out to all homes and small businesses in Great Britain, submit readings automatically to your energy supplier, with no need for any arithmetic from you.
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Many gas meters in the UK have a large “m³” printed on them. These are metric gas meters, introduced in 1995. Today, most gas meters that haven’t been replaced by smart meters are metric meters. They display your natural gas consumption by volume in cubic metres, or m³.
The other type of old gas meter is an imperial meter. Imperial meters are no longer being installed, but there are still a few of them hanging around. They should have “cubic feet”, or “ft³”, on the front.
To convert gas units on a metric meter (m³) to kilowatt-hours (kWh), follow these steps:
The formula is:
cubic meters of gas used x calorific value (usually 40.0) x correction factor (1.02264) ÷ 3.6 = kWh of gas
As an example, here are the calculations if you used 100 cubic metres of gas:
100m³ x 40 x 1.02264 ÷ 3.6 = 1,136kWh
To convert gas units on an imperial meter (ft³) to kilowatt-hours (kWh), follow these steps:
The formula is:
value your meter says you’ve used (in hundreds of cubic feet) x 2.83 x calorific value (usually 40.0) x correction factor (1.02264) ÷ 3.6 = kWh of gas
As an example, here are the calculations if you used 100 cubic feet of gas:
1 x 2.83 x 40.0 x 1.00264 ÷ 3.6 = 32.156kWh
You pay for gas by the kilowatt-hour. If you multiple your gas usage in kilowatt-hours by your per-unit charge, you’ll get the amount you’ll pay for your gas.
That won’t be the only line item on your gas bill. You’ll also pay a standing charge, which reflects the cost of maintaining your supply and servicing your account. Standing charges vary between suppliers, from 25p to £1.30 per day.
But your per-unit gas rate will make up a large part of your bill. Finding a cheaper rate can therefore reduce your energy costs.
Businesses, with widely differing energy consumption, often see energy prices represented as pence per kilowatt-hour. But households all have roughly similar energy usage and will usually see energy tariffs prices represented as the annual cost for a household with typical usage or the annual price for their projected consumption, based on their previous use.
Running an energy comparison can give you a survey of the tariffs available to you. If you’re a domestic customer, the tariffs will likely be represented as an overall annual cost, but you may be able to find the price per kilowatt-hour for with each.
However, you shouldn’t automatically jump on the cheapest per unit rate: it might come with a high daily standing charge that will erode your savings, especially if you don’t use a lot of energy.