Look at your gas meter and you'll see a number in cubic metres (m³) — not kilowatt-hours, not pounds. Your supplier does a real conversion behind the scenes to turn that volume reading into the energy figure your bill is actually based on, and the exact conversion factor shifts slightly day to day. Here's what's really happening, and what it means for a typical UK household.
Gas meters measure volume because that's what physically flows through the pipe. To convert that into energy (kWh), suppliers apply:
kWh = m³ × 1.02264 (volume correction factor) × calorific value ÷ 3.6
The 1.02264 factor corrects for temperature and pressure. The calorific value — how much energy a given volume of gas actually releases when burned — is published daily by National Grid for each network area, typically sitting between 39 and 40.5 MJ/m³ depending on where the gas in the network originated. This is the part that makes your bill impossible to predict to the penny from a generic calculator: the exact value your supplier used that day is on your bill, not in any general formula.
Ofgem publishes standard usage bands (Typical Domestic Consumption Values) so households can compare tariffs on a like-for-like basis. At the current price cap (7.33p/kWh, 29.04p/day standing charge):
| Usage band | Annual kWh | Annual cost | Monthly average |
|---|---|---|---|
| Low | 7,500 kWh | £656 | £55 |
| Medium | 12,000 kWh | £986 | £82 |
| High | 17,000 kWh | £1,352 | £113 |
A medium-usage household's 12,000 kWh converts to roughly 1,069 m³ on the meter over a year — the number that actually turns on your dial.
Enter two meter readings and get the exact kWh and cost, or estimate your bill directly from usage.
Use the Gas Calculator →At 29.04p/day, the standing charge alone is £106/year — before a single m³ is burned. It's identical whether you're a low or high user, which is why the gap between the low and high bands above (£656 vs £1,352) is driven almost entirely by usage, not the fixed portion.
At the current price cap, gas is 7.33p/kWh against electricity's 26.11p/kWh — gas costs roughly a third of electricity per unit of energy. That's the entire economic case for gas central heating over electric heaters, and why a heat pump's efficiency has to clear a real bar to compete on running cost alone.