📋 What This Guide Covers
- What "gas units" actually means and why the conversion is needed
- How to identify whether you have a metric or imperial gas meter
- The official Ofgem formula — explained in plain English
- Step-by-step conversion for metric meters (m³ → kWh)
- Step-by-step conversion for imperial meters (ft³ → kWh)
- Full worked examples for both meter types
- Quick estimate shortcuts for mental arithmetic
- 7 common mistakes and how to avoid them
- UK regional calorific values
What Are Gas Units?
A "gas unit" is simply the volume of natural gas your meter measures as it flows into your home. Your gas meter is essentially a volume counter — it measures how much physical gas passes through the pipe, not how much heat energy that gas delivers. The unit of measurement depends on the type of meter you have.
📊 Metric Meter (m³)
- 1 unit = 1 cubic metre (m³)
- Display shows 5 digits before decimal
- Labelled "m³", "M" or shows ³ symbol
- Standard in UK homes since mid-1990s
- 1 m³ ≈ 11.18 kWh (at avg CV)
- Most common type in UK today
🔢 Imperial Meter (ft³)
- 1 unit = 1 cubic foot (ft³)
- Display shows 4 digits, often with dials
- Labelled "ft³", "CF", "cubic feet" or "Hcf"
- Common in pre-1990s UK homes
- 1 ft³ ≈ 0.317 kWh (at avg CV)
- Must convert ft³ → m³ first
Your energy bill always charges you in kilowatt hours (kWh) — not in m³ or ft³. This is because the same volume of gas can contain slightly different amounts of heat energy depending on its composition, temperature and pressure. The conversion from volume to energy ensures every household is billed for the actual heat energy delivered, not just the physical volume of gas. All UK suppliers are legally required by Ofgem to use the same conversion formula.
The Official Ofgem Conversion Formula
Ofgem mandates a single conversion formula used by every UK domestic gas supplier — British Gas, Octopus Energy, EDF, Scottish Power, E.ON Next and all others. Understanding this formula means you can independently verify any gas bill in under two minutes.
Why the Formula Has Four Parts
- Calorific Value (CV) — Natural gas isn't uniform. Its heat content varies by source, season and region. The CV (printed on your bill) tells you how many kWh of heat are contained in exactly 1 m³ of your local gas supply. It typically ranges from 37.0 to 43.0 kWh/m³ across the UK.
- Volume Correction Factor (1.02264) — Gas expands in warm weather and contracts in cold. Your meter measures gas at local ambient conditions. The VCF of 1.02264 adjusts this to standard reference conditions (15°C, 1.01325 bar) so your bill is fair regardless of season or meter location.
- Division by 3.6 — By definition, 1 kWh = 3.6 megajoules (MJ). The CV × VCF calculation produces a result in MJ. Dividing by 3.6 converts this to the kWh figure shown on your bill.
- × 0.0283168 (imperial only) — This converts cubic feet to cubic metres before the rest of the formula is applied (1 ft³ = 0.0283168 m³).
How to Convert Gas Units to kWh — Metric Meter (m³)
Follow these five steps if your gas meter display shows m³, M or a ³ symbol. This covers the vast majority of UK homes with meters installed since the mid-1990s.
Find Your Gas Meter Readings
Locate your current gas meter reading — either on the physical meter or in your supplier's app if you have a smart meter. Write down the number shown before the decimal point (ignore any red digits). Your previous reading will be on your last bill or in your account's billing history.
Find Your Calorific Value
Look for "calorific value", "CV" or "energy content" in the billing breakdown section of your gas bill. Your supplier is legally required to print it. It will be a number between 37.0 and 43.0 — either in kWh/m³ (preferred) or MJ/m³. If shown in MJ/m³, divide by 3.6 to convert.
Multiply m³ by Calorific Value
Multiply your units used by the calorific value. This gives you the energy in the gas before correction for pressure and temperature conditions at your meter.
Multiply by Volume Correction Factor (1.02264)
Multiply the result by 1.02264 — Ofgem's standardised volume correction factor. This is always 1.02264 for UK domestic gas bills. You never need to calculate or look up this number.
Divide by 3.6 to Get kWh
Divide by 3.6 to convert from the megajoule intermediate value to kilowatt hours. This is your final answer — the kWh figure that should match your bill's "energy used" line.
How to Convert Gas Units to kWh — Imperial Meter (ft³)
Use these steps if your gas meter shows ft³, CF, cubic feet or Hcf. Imperial meters are common in UK homes built before the 1990s, particularly terrace houses, flats and older semi-detached properties. The process has one extra step compared to a metric meter — you must first convert cubic feet to cubic metres.
Read Your Imperial Gas Meter
Note down the current reading in cubic feet. Imperial meters typically have four dials or a digital display showing four main digits. Read dials left to right, taking the lower number when a needle sits between two digits. Ignore any red dials. Subtract your previous reading to find units used.
Convert Cubic Feet to Cubic Metres
Multiply your cubic feet reading by 0.0283168 to convert to cubic metres. This is the standard conversion factor (1 cubic foot = 0.0283168 m³). Your bill may show this step as "multiply by 2.83 and divide by 100" — it's the same thing.
Find Your Calorific Value
Locate the calorific value on your gas bill — exactly as described for metric meters above. The same CV applies regardless of your meter type. UK average is 39.5 kWh/m³.
Apply the Ofgem Formula
Now your reading is in m³, apply the same formula as a metric meter: multiply by the calorific value, then by 1.02264, then divide by 3.6.
Verify Against Your Bill
Your calculated kWh should match the energy used figure on your bill. A difference of up to 2–3 kWh is normal due to rounding in the calorific value. A larger difference usually means your supplier used an estimated reading or applied a different CV for part of the billing period.
⚡ Skip the Maths — Use Our Free Calculator
Our calculators apply the full Ofgem formula automatically. Just enter your readings and get your kWh result instantly — with a complete formula breakdown showing every calculation step.
Quick Estimate Shortcuts (No Calculator Needed)
When you need a rough figure without going through the full formula — for a quick sanity check on your bill or a mental estimate — these simplified multipliers work within 2–4% for most UK regions.
⚡ Quick Conversion Shortcuts (UK 2026)
Actual: 964.98 kWh (error: 0.2%)
Actual: 136.62 kWh (error: 0.06%)
Use for reverse estimates only
UK avg: 31–40 kWh/day in winter
UK Regional Calorific Values 2026
The calorific value (CV) is the single most important variable in the gas-to-kWh conversion. Using the wrong CV — or ignoring it entirely and just multiplying by a round number — introduces billing errors. The table below shows typical ranges by UK region. Always use your bill's stated CV for exact results.
| UK Region | CV Range (kWh/m³) | Band | kWh per m³ (avg) | kWh per ft³ (avg) |
|---|---|---|---|---|
| 🇬🇧 UK National Average | 38.5 – 40.5 | Average | ≈ 11.18 kWh | ≈ 0.317 kWh |
| London & South East | 39.0 – 41.5 | Above Avg | ≈ 11.44 kWh | ≈ 0.324 kWh |
| South West England | 38.8 – 41.0 | Average | ≈ 11.34 kWh | ≈ 0.321 kWh |
| East Anglia & East Midlands | 39.0 – 40.8 | Average | ≈ 11.34 kWh | ≈ 0.321 kWh |
| West Midlands | 38.5 – 40.5 | Average | ≈ 11.18 kWh | ≈ 0.317 kWh |
| Yorkshire & Humber | 38.0 – 40.2 | Average | ≈ 11.11 kWh | ≈ 0.315 kWh |
| North West England | 37.8 – 40.0 | Below Avg | ≈ 11.06 kWh | ≈ 0.313 kWh |
| North East England | 37.5 – 39.8 | Below Avg | ≈ 10.98 kWh | ≈ 0.311 kWh |
| Scotland (Central) | 37.5 – 40.0 | Below Avg | ≈ 11.01 kWh | ≈ 0.312 kWh |
| Scotland (North) | 37.2 – 39.5 | Below Avg | ≈ 10.90 kWh | ≈ 0.309 kWh |
| Wales | 38.0 – 40.2 | Average | ≈ 11.11 kWh | ≈ 0.315 kWh |
| Northern Ireland | 38.0 – 40.0 | Average | ≈ 11.08 kWh | ≈ 0.314 kWh |
kWh per unit values calculated using mid-range CV, VCF 1.02264 and dividing by 3.6. ft³ values additionally apply 0.0283168 ft³→m³ conversion. Source: National Grid Gas Transmission. Seasonal variation ±1.5 kWh/m³ typical.
7 Common Mistakes When Converting Gas Units to kWh
These are the errors that most frequently cause a calculated kWh to differ significantly from the bill figure — and in some cases, cause people to miss genuine billing errors.
How to Read Your Gas Meter
Reading a Digital Metric Meter
Digital metric meters display a row of digits on an LCD or LED screen. Read the 5 digits shown in black or white from left to right — these are your cubic metre reading. Ignore any digits shown in red, after a decimal point, or labelled as "× 10". If your display cycles through multiple readings, the gas consumption reading is usually labelled "V1" or shown first in the cycle.
Reading an Old-Style Imperial Dial Meter
Imperial dial meters have a row of dials, each numbered 0–9. Read them left to right. For each dial: if the needle is between two numbers, write down the lower number. If the needle appears to be exactly on a number, write it down but check the dial to the right — if that dial hasn't yet reached zero, subtract one from your reading. Ignore any red dials. The result is your reading in hundreds of cubic feet (Hcf) or cubic feet (ft³) depending on the meter model.
Reading a Smart Meter
Smart meters have a digital display that automatically sends readings to your supplier. Your In-Home Display (IHD) unit shows gas usage in kWh directly — the conversion has already been done by the meter's software. If your IHD shows m³ instead of kWh, press the "B" button or cycle through screens until you find the kWh view. For manual verification, note the m³ reading shown and apply the steps in this guide.