UK GHG Conversion Factors 2026: DESNZ Factors Explained

Written by Calvin Lo, Founder of Aphelios Software | August 2026 | 6 min read

Every SECR report in the UK is built on the same foundation: the UK Government’s Greenhouse Gas Conversion Factors for Company Reporting, published by the Department for Energy Security and Net Zero (DESNZ). These factors turn activity data - kilowatt-hours of electricity, litres of diesel, miles of business travel - into tonnes of CO2 equivalent (CO2e).

If you have ever opened the DESNZ "flat file" spreadsheet, you know the challenge: it contains thousands of rows across worksheets, with columns for each gas and unit, and one header row that determines the data year. This guide explains what the factors are, how to apply them, and why getting the version right matters more than getting the arithmetic right.

What Are the DESNZ Conversion Factors?

The factors are published annually (typically each June) and cover:

• Electricity - the UK grid average factor, which changes every year as the grid decarbonises
• Fuels - natural gas, diesel, petrol, LPG, biomass and more, with separate factors for combustion CO2, methane and nitrous oxide
• Transport - business travel by car, rail, air, sea and bus
• Scope classifications - each row is labelled Scope 1, 2 or 3 as printed by DESNZ

The figures are expressed in kgCO2e per unit of activity, and use IPCC AR5 Global Warming Potential (GWP-100) values, per the Environmental Reporting Guidelines (SECR chapter).

How to Calculate Emissions from Activity Data

The calculation is always the same shape:

Example: 12,400 kWh of electricity in 2025 multiplied by the 2025 grid factor of 0.11406 kgCO2e/kWh gives approximately 1,414 kgCO2e - about 1.41 tonnes. Divide by 1,000 to convert from kg to tonnes, and that figure goes into your report.

Why the "Flat File" Is a Trap for Spreadsheet Users

The official DESNZ publication ships as a large workbook with a "Factors by Category" worksheet and a header layout that carries the data year (for example "GHG Conversion Factor 2026"). Common spreadsheet failures include:

• Copying a factor from last year’s file into this year’s report (grid factors fall every year, so this overstates emissions)
• Using the wrong unit column - kWh vs MWh, litres vs tonnes, miles vs km
• Missing the biogenic CO2 rows, which must be reported separately and excluded from totals
• No record of which factor version a number came from, which an auditor cannot verify

Software removes all of these failure modes. Aphelios imports the official flat file directly: a System Admin uploads the workbook once, the data year is read from the file header, and the factor set is versioned and archived automatically. Every activity you record then pulls from the correct set for its year, so a "factor drift" error is impossible.

Factor Versioning and Archiving

Because factors change annually, good records keep every set. In Aphelios, one factor set is marked current at a time and the others are archived - so last year’s report can still be reconstructed with exactly the factors that were current when it was prepared. That is the kind of detail that survives an audit unscathed.

UK GHG Conversion Factors FAQ

This guide is a planning aide, not legal advice. Confirm your reporting approach with your accountant before filing.