DEFRA conversion factors explained (2026)

The DEFRA conversion factors are the UK government’s official figures for turning business activity, like kWh of electricity or litres of diesel, into greenhouse gas emissions. The 2026 set was published on 11 June 2026 by the Department for Energy Security and Net Zero (DESNZ) and is intended for reporting activity that takes place in 2026. The headline change is electricity: the UK grid factor fell by about 26%, to 0.13096 kg CO2e per kWh.

If you’re putting together a carbon footprint for a customer, a grant or a tender, these are the factors to use. Here’s what they are, what changed this year and how to pick the right set.

Who publishes the conversion factors, and why are they still called DEFRA factors?

The official title is the UK Government GHG Conversion Factors for Company Reporting. They were first published by DEFRA, moved to BEIS, and have been published by DESNZ since 2023. The old name stuck, which is why most people still search for DEFRA conversion factors.

A new set comes out every year, usually in early June, on the government conversion factors collection page. Each release includes:

• The full set, an Excel workbook with a worksheet for each type of activity and guidance notes. This is the one most people should use.
• The flat file, the same factors in a single table for software and automatic processing.
• A methodology paper explaining how every factor is calculated.
• A major changes report listing anything that moved by more than 5% (Scope 1 and 2) or 10% (Scope 3).

They’re designed for UK organisations of every size and are the basis of SECR reporting for large companies. For a small business, they’re simply the most credible factors you can cite.

What changed in the 2026 conversion factors?

According to the 2026 major changes report, the changes most likely to affect a small business are:

• Electricity is down about 26%. DESNZ changed the method so the data now lags the publication year by one year instead of two. That means this year’s drop captures two years of grid changes at once. Changes in the generation mix, grid losses and calculation improvements also play a part.
• Electric vehicle factors are down 23% to 26% for most cars, following the electricity change.
• National rail is down 13%, reflecting updated passenger numbers and fleet data that had last been refreshed using pre-pandemic figures.
• Homeworking office equipment is down about 31%, again because of electricity. The homeworking heating factor is unchanged since 2022.
• Aviation and water factors were held constant from 2025.
• Natural gas, petrol and diesel moved only slightly.

There was also a small correction on 31 July 2026. The flat file was republished because some well-to-tank and hotel values had shown as zero rather than blank. The full set wasn’t affected.

Which year’s conversion factors should you use?

Use the set that matches when the activity happened. The 2026 factors are for activity in 2026, the 2025 factors for activity in 2025, and so on.

If your reporting period crosses two calendar years, a common approach is to use the set for the year containing the midpoint of the period. That’s what the ESG Now questionnaire does:

• January to December 2026: midpoint in 2026, so the 2026 set.
• April 2025 to March 2026: midpoint around the end of September 2025, so the 2025 set.
• October 2025 to September 2026: midpoint around April 2026, so the 2026 set.

Whatever you choose, state the factor year in your report. Anyone checking your figures will look for it.

The 2026 factors most small businesses need

You won’t need most of the workbook. These are the figures that come up for a typical office, shop or service business, rounded and approximate. Always take exact values from the full set.

Activity	Approximate 2026 factor	Scope
UK grid electricity	0.131 kg per kWh	2
Natural gas	0.182 kg per kWh	1
Diesel (average biofuel blend)	2.58 kg per litre	1
Petrol (average biofuel blend)	2.08 kg per litre	1
Average petrol car	0.26 kg per mile	1 or 3
Average diesel van (up to 3.5 tonnes)	0.41 kg per mile	1
Battery electric car, charging	0.043 kg per mile	2
National rail	0.031 kg per passenger km	3
Domestic flight, with radiative forcing	0.229 kg per passenger km	3
Short-haul economy, with radiative forcing	0.126 kg per passenger km	3
Long-haul economy, with radiative forcing	0.117 kg per passenger km	3
Water supply and treatment combined	0.36 kg per cubic metre	3
Commercial waste to landfill	521 kg per tonne	3
Commercial waste to energy recovery	4.7 kg per tonne	3

If you need homeworking emissions, the combined 2026 factor is about 0.324 kg CO2e per full-time equivalent working hour, reported in Scope 3. Our working-from-home guide explains the method.

A car is Scope 1 if the business owns or leases it, and Scope 3 if it’s an employee’s own car on a mileage claim. Our guide to Scope 1, 2 and 3 emissions explains the split.

Your electricity emissions dropped. Is that real?

Partly. If you used the same 10,000 kWh in 2025 and 2026, your location-based electricity emissions would fall from about 1.77 tonnes to about 1.31 tonnes, without you changing anything. The grid really has got cleaner, but you haven’t done anything to earn that reduction, and a careful reader will know it.

Three habits keep your reporting honest:

• Show kWh alongside tonnes. If your kWh went down, that’s your achievement. If it didn’t, the reader can see the factor did the work.
• Mention the method change if you’re comparing 2026 with earlier years. The 2026 methodology paper notes that users should decide whether to adjust earlier figures for a consistent time series.
• Report market-based Scope 2 too. If you’re on a REGO-backed renewable tariff, your market-based figure is zero regardless of the grid factor. See location-based vs market-based.

How do you use the factors in practice?

The sum is always the same: activity × factor = kg CO2e. Divide by 1,000 for tonnes of CO2e.

A few tips from the workbook itself:

• Use the kg CO2e column, which combines all the greenhouse gases. The separate CO2, methane and nitrous oxide columns are there for detailed reporting.
• Check the unit. Gas comes in kWh (gross calorific value), cubic metres or tonnes. Mixing them up is the most common mistake.
• Use gross CV for gas in kWh, which matches what UK bills show.
• Well-to-tank and transmission and distribution factors are separate, optional Scope 3 extras. Leave them out unless someone asks, and say so.

If you’d rather not touch the spreadsheet at all, the ESG Now questionnaire applies the correct factor year automatically and shows every line of working in the appendix. It covers heating fuels, company vehicles, refrigerants, electricity, EV charging, water, waste, deliveries, business travel, commuting and homeworking. Most small businesses finish in under 30 minutes. Start your free report, or see how it fits on our small businesses page.