UK emissions factors: which set to use, and how
Every UK carbon report rests on the same engine: activity data multiplied by a conversion factor. The factors are published annually by DESNZ, and most reporting errors trace back to using the wrong year-set, or confusing location-based and market-based electricity. This page explains which factors to use, how to apply them, and where the official dataset lives.
What the UK conversion factors are
The UK greenhouse gas conversion factors for company reporting are a single, free dataset published every year by the Greenhouse Gas Inventory team in the Department for Energy Security and Net Zero[1].
They were historically published under DEFRA, but DESNZ now produces them. Their job is narrow and important: turn an organisation’s activity data into tonnes of carbon dioxide equivalent so it can report under Streamlined Energy and Carbon Reporting and other frameworks[3].
The factors are built primarily on the National Atmospheric Emissions Inventory, compiled to the IPCC 2006 Guidelines, which is why DESNZ describes them as a high-quality tool that can be relied on year on year[3].
They are a tool, not a statistic in themselves — but DESNZ voluntarily applies the Code of Practice for Statistics to their production, which is what gives them their authority[3].
Which year’s factors to use
The single most common error is using the wrong year-set. The rule is simple: use the factors for the year your reporting period falls in, not the year you compile or submit the report[2].
If your reporting year is 2025, you use the 2025 conversion factors — even if you are pulling the report together in 2026. A new set is published annually, so each reporting year has its own matching factors[2].
DESNZ keeps every year-set in a single collection, so older sets remain available alongside the latest one. That is deliberate: it lets you report a prior year correctly rather than forcing the newest figures onto it[2].
| Reporting period | When you report | Factor set to use |
|---|---|---|
| 2024 reporting year | Compiled in 2025 | 2024 conversion factors |
| 2025 reporting year | Compiled in 2026 | 2025 conversion factors |
| 2026 reporting year | Compiled in 2027 | 2026 conversion factors (once published) |
When a single report spans more than one year — for example, a trend comparison — each year is converted using its own set. Mixing sets within one calculation distorts the comparison you are trying to make[2].
How a conversion factor is applied
Every emissions calculation reduces to the same arithmetic: activity data multiplied by the matching conversion factor gives tonnes of CO2 equivalent[1].
Activity data is whatever you can measure from invoices and records — kilowatt-hours of electricity, cubic metres or kilowatt-hours of gas, litres of fuel, or kilometres travelled. The factor translates each unit into emissions[5].
The discipline is in the matching. The factor must align with the activity on four fronts at once: the right fuel or activity, the right unit, the right energy basis, and the right reporting year.
| Activity data | Conversion factor | Result |
|---|---|---|
| Electricity consumed (kWh) | Grid-average electricity factor | Scope 2 location-based tCO2e |
| Natural gas (kWh, gross CV) | Natural gas factor | Scope 1 tCO2e |
| Fuel purchased (litres) | Fuel-specific factor | Scope 1 fleet tCO2e |
| Distance travelled (km) | Mode-specific travel factor | Scope 3 business-travel tCO2e |
Location-based versus market-based Scope 2
Purchased electricity is the part of the calculation most often misreported, because there are two legitimate methods and they answer different questions[4].
The location-based method uses the average emissions intensity of the grid where the electricity is consumed. For UK consumption that is the DESNZ grid-average electricity factor, which reflects the average carbon intensity of the grid mix[4].
The market-based method reflects the electricity a company has contractually chosen. Its factors come from contractual instruments — renewable supply contracts, REGO-backed tariffs, or the residual mix where no specific contract applies[4].
The GHG Protocol Scope 2 Guidance requires companies that operate in markets offering contractual instruments to report both figures. This is dual reporting, and it exists so that the two views — grid reality and procurement choice — can be tracked side by side[4].
| Dimension | Location-based | Market-based |
|---|---|---|
| What it reflects | Average intensity of the grid you draw from | Electricity you have contractually chosen |
| Factor source | DESNZ grid-average electricity factor | Contractual instruments (supply contracts, REGOs) |
| Renewable contract effect | No change — grid average still applies | Can reduce the figure where criteria are met |
| GHG Protocol status | Always reported | Also reported where contractual data exists (dual reporting) |
A frequent mistake is to count the same electricity twice — claiming a renewable contract under the market-based method while also discounting the location-based figure. Each method is reported on its own terms; they are not combined[4].
The common mistakes
Most conversion-factor errors are not exotic. They cluster around a handful of recurring traps, and each has a clear fix.
| Mistake | Why it is wrong | Fix |
|---|---|---|
| Wrong year-set | A fresh set is published each year, so the wrong one misstates emissions | Match the set to the reporting period, not the submission date |
| Mixing methods on Scope 2 | Location-based and market-based answer different questions | Report each on its own terms; do not blend them |
| Double counting electricity | Claiming a renewable contract and discounting the grid figure counts it twice | Keep location-based and market-based separate |
| Wrong energy basis | UK gas is billed on gross CV; the net-CV factor gives a different result | Use the gross-CV factor where the bill is on a gross basis |
| UK factors abroad | Each country has a different grid intensity | Use the international electricity factors in the DESNZ set |
For the value-chain side of the calculation, the same matching discipline applies but the data is harder to obtain. See our guide to Scope 3 emissions reporting for how to handle business travel, purchased goods and the rest of the value chain.
How the factors support SECR and UK SRS S2
The conversion factors are not an end in themselves — they are the input that makes carbon reporting frameworks work.
Under SECR, qualifying companies report energy use and the resulting greenhouse gas emissions, and the DESNZ factors are the standard tool DESNZ provides for that conversion[3].
Under UK SRS S2, the UK climate disclosure standard, in-scope companies must report gross Scope 1, Scope 2 and Scope 3 emissions measured in line with the GHG Protocol Corporate Standard[4].
Because the DESNZ factors are a recognised input for the GHG Protocol calculation, the same dataset that has long served SECR also feeds the newer UK SRS S2 reporting — one factor source, two regimes[4].
Downloading the official dataset
There is one authoritative home for the figures, and it is not a third-party summary: the DESNZ publication on GOV.UK. The 2025 set is provided as a condensed set for most users, a full set for advanced users, and a flat file for automated processing, alongside the methodology and major-changes papers[1].
New users are pointed to the introductory worksheet in the condensed set; regular users are directed to the “what’s new” sheet that flags the significant changes for that update, which is how you keep year-on-year reporting consistent[1].
Every year-set lives in the DESNZ collection, so once the next set is published it appears there alongside the previous ones. Bookmark the collection rather than a single year’s file[2].
Download the 2025 conversion factors from GOV.UK or browse the full annual collection.
UK emissions factors: frequently asked questions
Who publishes the UK greenhouse gas conversion factors?
The UK greenhouse gas conversion factors for company reporting are published annually by the Greenhouse Gas Inventory team in the Department for Energy Security and Net Zero (DESNZ). They were historically badged under DEFRA, but DESNZ now produces them. They are a free resource that lets organisations convert activity data into tonnes of carbon dioxide equivalent (tCO2e), and they underpin Streamlined Energy and Carbon Reporting (SECR). The factors are based primarily on the National Atmospheric Emissions Inventory, compiled to the IPCC 2006 Guidelines.
Which year of conversion factors should I use?
Use the conversion factors for the year your reporting period falls in, not the year you happen to be submitting the report. If you are reporting emissions for the 2025 reporting year, use the 2025 conversion factors — even if you are compiling the report in 2026. A new set is published each year, so mixing years within a single report, or defaulting to the latest set because it is the most recent file, is a common source of error.
What is the difference between location-based and market-based Scope 2?
The location-based method uses the average emissions intensity of the grid where the electricity is consumed — for UK consumption, the DESNZ grid-average electricity factor. The market-based method reflects the electricity a company has contractually chosen, using emission factors derived from contractual instruments such as renewable supply contracts or REGO-backed tariffs. The GHG Protocol Scope 2 Guidance requires companies with operations in markets that offer contractual instruments to report both figures — known as dual reporting.
How are the conversion factors actually used in a calculation?
The core calculation is activity data multiplied by the relevant conversion factor. For example, kilowatt-hours of electricity, litres of fuel or kilometres travelled are each multiplied by the matching factor to give tonnes of CO2 equivalent. The discipline is in matching the factor to the activity exactly: the right fuel, the right unit, the right energy basis (gross versus net calorific value), and the right reporting year.
How do the conversion factors relate to SECR and UK SRS?
SECR requires qualifying companies to report energy use and the resulting greenhouse gas emissions, and the DESNZ conversion factors are the standard tool for that conversion. UK SRS S2, the UK climate disclosure standard, requires gross Scope 1, Scope 2 and Scope 3 emissions measured in line with the GHG Protocol Corporate Standard. The DESNZ factors are a recognised input for the GHG Protocol calculation, so the same factor set supports both the existing SECR regime and the emerging UK SRS S2 reporting.
- Greenhouse gas reporting: conversion factors 2025 — GOV.UK / Department for Energy Security and Net Zero · Condensed, full and flat-file sets, plus methodology and major-changes papers
- Government conversion factors for company reporting of greenhouse gas emissions — GOV.UK / DESNZ · Annual collection — each year-set sits here once published
- Conversion factors 2025: statement of voluntary compliance with the Code of Practice for Statistics — GOV.UK / DESNZ · Confirms annual publication by the GHGI team, use for SECR, and NAEI / IPCC 2006 basis
- GHG Protocol Scope 2 Guidance — Greenhouse Gas Protocol · Defines location-based and market-based methods and the dual-reporting requirement
- Environmental reporting guidelines: including Streamlined Energy and Carbon Reporting requirements — GOV.UK / DESNZ · How the factors are applied under SECR