Gas Meter Units Explained — m³ vs kWh

Your gas meter shows one number. Your bill shows a completely different one. If you’ve ever wondered why — this is the page that explains it clearly, once and for all.

Why your meter and your bill show different numbers

Gas meters in the UK measure how much gas you physically use — in volume. But energy suppliers charge you for the energy that gas produces — in kilowatt hours (kWh). These are two different things, which is why the numbers never match directly.

Think of it like this: your meter measures how many litres of petrol went into your tank. Your bill charges you for how far that petrol took you. The conversion happens in between.

What is m³?

m³ stands for cubic metres. Most modern gas meters in the UK display usage in cubic metres. One cubic metre is the volume of a cube measuring one metre on each side — it’s purely a measurement of how much space the gas takes up.

Older meters may display in hundreds of cubic feet (ft³). If your meter shows ft³, there’s a different conversion factor involved — our calculator handles both.

What is kWh?

kWh stands for kilowatt hour. It’s a unit of energy — specifically, the amount of energy used by a one kilowatt appliance running for one hour. Your energy supplier uses kWh because it reflects the actual energy value of the gas, not just its volume.

This is the number that appears on your bill and determines what you pay.

How does the conversion work?

To convert m³ to kWh, your supplier applies a formula using two factors:

Calorific value — the amount of energy in the gas (varies slightly by region and supplier, typically around 39-40)
Volume correction factor — adjusts for temperature and pressure (standard value is 1.02264)

The full formula is:

kWh = m³ used × calorific value × volume correction factor ÷ 3.6

In practice this means every cubic metre of gas is worth roughly 11 kWh — but the exact figure varies, which is why checking your own bill matters.

Skip the maths — use our gas meter reading to kWh calculator →

Why does this matter for your bill?

If your supplier applies the wrong calorific value, or uses the wrong unit type (treating ft³ as m³ for example), your bill can be significantly wrong. This isn’t theoretical — it happens, and customers are often none the wiser because the numbers mean nothing without context.

Knowing how the conversion works means you can check your own bill figures in minutes.

How to check your own figures

Take a reading from your meter and note the unit type (m³ or ft³)
Find your calorific value on your bill (usually in small print)
Use our calculator to convert to kWh
Compare to what your supplier has charged

If the figures don’t match, you have grounds to query your bill.

Convert your gas reading to kWh now →

What if your meter shows ft³ instead of m³?

Older imperial meters display in hundreds of cubic feet. The conversion is slightly different but the principle is the same — our calculator handles both unit types automatically. Just select the correct unit when you enter your reading.

Gas meter reading to kWh calculator (m³ and ft³) →

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All advice on SmartMeterHelp is independent. We’re not affiliated with any energy supplier.