One number for several gases
Your business doesn't only emit carbon dioxide. A gas boiler also gives off small amounts of methane and nitrous oxide. Air conditioning leaks hydrofluorocarbons. Reporting each gas separately would be confusing, and you couldn't add them up, because a kilogram of one gas warms the planet far more than a kilogram of another.
CO2e solves that. Each gas is converted into the amount of carbon dioxide that would cause the same warming, and then everything is added together. That is why carbon footprints, Carbon Reduction Plans and SECR reports are all in tonnes of CO2e.
Global warming potentials
The multiplier for each gas is its global warming potential, or GWP. It compares the warming from releasing 1 kg of the gas with releasing 1 kg of CO2, added up over 100 years. The values come from the Intergovernmental Panel on Climate Change (IPCC). The UK government's 2026 factors use these:
| Gas | kg CO2e per kg (2026) | Where a small business meets it |
|---|---|---|
| Carbon dioxide (CO2) | 1 | Burning gas, oil, diesel and petrol |
| Methane (CH4) | 28 | Small amounts from burning fuel; food and paper breaking down in landfill |
| Nitrous oxide (N2O) | 265 | Small amounts from burning fuel |
| HFC-32 (R32) | 677 | Most new air conditioning and many heat pumps |
| R410A (a blend of HFCs) | 1,924 | Older office air conditioning |
So releasing a tonne of methane counts as 28 tonnes of CO2e. At the top of the scale, 1 kg of sulphur hexafluoride is 23,500 kg CO2e. The GHG Protocol and the PPN 006 technical standard both cover the same seven gases named in the Kyoto Protocol: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride.
Why methane counts more, and why that matters
Methane traps much more heat per kilogram than CO2, but it doesn't last: the IPCC puts its lifetime in the atmosphere at about 12 years, while CO2 stays for far longer. The 100-year GWP weighs both: added up over a century, a kilogram of methane still causes 28 times the warming of a kilogram of CO2. Company reporting in the UK uses these 100-year values.
For a small business, the gases other than CO2 matter most in two places:
- Waste to landfill. Food, paper and card break down in landfill and give off methane, and the government's landfill factors are built from a model of that methane. See our post on waste emissions from your contractor's data.
- Refrigerants. The same idea in the extreme: 1 kg of R410A is 1,924 kg CO2e.
A worked example
A small office burns 40,000 kWh of gas a year, and its air conditioning engineer tops up 2 kg of R410A. Both are Scope 1, and the government factors are already in CO2e:
- Gas: 40,000 kWh × 0.18231 = 7.29 tonnes CO2e. The small amounts of methane and nitrous oxide from combustion are already inside the factor.
- Refrigerant: 2 kg × 1,924 = 3.85 tonnes CO2e.
2 kg of leaked gas counts for 53% as much as a year of heating. That comparison is only possible because both are in CO2e. Our post on refrigerant leaks covers where to find the top-up figures.
The values change now and then
The IPCC updates its GWPs in each assessment report, and the UK factors follow when the international reporting rules do. The government sets moved to newer values in 2023, which nudged some factors up and others down. Our post on AR5 and AR6 global warming potentials explains which values the UK uses and what a buyer might ask about them.
How Carbon Recycling helps
You never have to convert gases yourself. Carbon Recycling turns kWh, litres, miles, kilograms of refrigerant and tonnes of waste into kg CO2e using the government factor for each entry's year, and every line shows the factor it used. To try it on a bill, use the free kWh to CO2e calculator, or read Scope 1, 2 and 3 explained for where each gas lands in your footprint.