ESG glossary
DEFRA conversion factors
DEFRA conversion factors are the UK government's official numbers for turning business activity, such as kWh of electricity or litres of diesel, into greenhouse gas emissions in kg CO2e. They are now published each year by DESNZ.
The official name is the UK Government GHG Conversion Factors for Company Reporting. They were originally published by DEFRA, which is why most people still call them “DEFRA factors”, but they are now produced by the Department for Energy Security and Net Zero (DESNZ). A new set comes out every year, usually in June.
What it means for a small business
If you calculate a carbon footprint in the UK, these are the factors buyers, funders and assessors expect you to use. They cover almost everything a small business does: electricity, gas, vehicle fuels, flights, rail, hotels, waste and water.
The basic calculation is always the same: activity × factor = emissions. You take your activity data in the right unit and multiply it by the matching factor to get kg CO2e.
Two things to watch:
- Use the right year. The set should match your reporting period. Using an old electricity factor can noticeably overstate your footprint, because the UK grid gets cleaner most years.
- Use the right factor. Gas billed in kWh is usually on a gross calorific value basis, and flights have separate factors with and without radiative forcing.
The 2026 set was published on GOV.UK in June 2026. Its UK electricity factor fell to about 0.131 kg CO2e per kWh, from 0.177 in the 2025 set, partly because of a cleaner grid and partly a change of method.
An example
A business uses 30,000 kWh of electricity in 2026. Using the 2026 factor, that is 30,000 × 0.13096 = about 3,930 kg, or 3.9 tCO2e. With the 2025 factor, the same use would show 5.3 tonnes.
How ESG Now handles it
The ESG Now questionnaire applies the UK government factors automatically, matching the factor year to the midpoint of your reporting period. Every factor used is listed in the report appendix. Read more in our DEFRA conversion factors 2026 guide or on the methodology page.
Guides that cover this
- Carbon footprintDEFRA conversion factors explained (2026)The 2026 UK government factors were published in June 2026, and the electricity factor dropped sharply. Here is what changed, which set to use and the handful of figures most small businesses need.Read the guide →
- Carbon footprintHow to calculate your small business carbon footprintMultiply what you use by the official UK factors and add it up. Here is exactly what to measure, a worked example, and what to do when you are missing a bill.Read the guide →
- Carbon footprintScope 1, 2 and 3 emissions explained for small businessesScope 1 is fuel you burn, Scope 2 is electricity you buy, Scope 3 is everything else. Here is how each one applies to a real small business.Read the guide →