What are conversion factors?
A conversion factor turns something you can measure, such as kWh of electricity or litres of diesel, into the greenhouse gas emissions it causes, in kg of carbon dioxide equivalent (CO2e). The UK government publishes a new set every year for company reporting. They are what PPN 006 Carbon Reduction Plans and SECR reports expect you to use.
What changed in 2026?
| Activity | Per | 2025 (kg CO2e) | 2026 (kg CO2e) | Change |
|---|---|---|---|---|
| UK grid electricity | kWh | 0.17700 | 0.13096 | -26.0% |
| Natural gas | kWh (gross CV) | 0.18296 | 0.18231 | -0.4% |
| Diesel (forecourt) | litre | 2.57082 | 2.58354 | +0.5% |
| Petrol (forecourt) | litre | 2.06916 | 2.07500 | +0.3% |
| Average car, unknown fuel | mile | 0.26915 | 0.26699 | -0.8% |
| National rail | passenger km | 0.03546 | 0.03092 | -12.8% |
Values are the total kg CO2e factors for the seven greenhouse gases, taken from the official DESNZ flat files.
The big story is electricity. The grid factor reflects how the UK's electricity is generated, and with more wind and solar and less gas, it has fallen sharply. Fuels like gas and diesel are chemically the same each year, so their factors only shift slightly with the biofuel blend and method updates.
Why your footprint may drop without you doing anything
If your electricity use stayed the same, your Scope 2 emissions will fall by about 26% when you move from the 2025 to the 2026 factors. For an office using 50,000 kWh a year, that is 8.85 tonnes in 2025 and 6.55 tonnes in 2026. It is a genuine change in the carbon intensity of your electricity, but it isn't a reduction your business made. Say so in your report, and show your own reductions separately. Our kWh to CO2e calculator shows both years side by side.
Which year's factors should I use?
- Use the set for the year your reporting period falls in. A January to December 2026 year uses the 2026 set.
- If your year spans two calendar years, use the set for the calendar year that most of it falls in. An April 2026 to March 2027 year uses 2026; a July 2025 to June 2026 year uses 2026 as well.
- Keep the same rule every year, and say which set you used in your methodology.
- Don't recalculate past years with new factors unless you are correcting an error or your business has changed shape, for example through an acquisition.
How Carbon Recycling handles it
We load every DESNZ set from 2019 to 2026 straight from the official files. Each entry uses the set for its own reporting year, and every figure shows the factor's ID, year and value, so anyone can check it. Read the details in our methodology.