DEFRA conversion factors 2025: how to use them for SECR

What the DEFRA conversion factors are

The UK Government GHG conversion factors for company reporting are the default emission factors for UK greenhouse gas reporting, including SECR and ESOS. They are published annually — originally by DEFRA, now jointly with DESNZ (the Department for Energy Security and Net Zero). The current set is the 2025 edition, published in June 2025 for reporting 2025 emissions.

An emission factor is the greenhouse gas produced per unit of activity — kgCO₂e per kWh of electricity, or per litre of diesel. You multiply your activity data by the matching emission factor to convert consumption into carbon emissions. These emission conversion factors give every UK organisation one consistent basis to report greenhouse gas emissions, and let you calculate your carbon footprint from real consumption data — the foundation of credible carbon accounting and carbon footprinting.

The publication is a single Excel workbook covering:

• Fuels — natural gas, oil products, biofuels, hydrogen, coal (per kWh or per litre)
• UK grid electricity — location-based, per kWh
• Transport and freight — road, rail, air, sea, by vehicle type and distance
• Refrigerants — per kg, using IPCC global warming potentials
• Water, waste, materials, hotel stays and homeworking
• Scope 3 categories such as well-to-tank and transmission and distribution (T&D) losses

Why the 2025 DEFRA emission factors matter for SECR

Under the GHG Protocol Corporate Standard used for SECR you may use any credible emission factor, but in UK practice the DEFRA conversion factors are the de facto choice for three reasons: auditors and the FRC are familiar with them; they cover virtually every UK emission source; and they are the factors the UK Government uses in its own reporting. There is no legal mandate to use DEFRA factors specifically, but deviating is rare and must be justified in your methodology statement.

This catches more companies than expected. The April 2025 Companies Act uplift raised the general "large" company test to turnover of £54M and a balance sheet of £27M — but the SECR thresholds did not move. SECR still applies if you meet two of three: turnover of £36M or more, a balance sheet of £18M or more, or 250 or more employees. A company that is now "medium" under the new accounting limits can still be in SECR scope — and still needs the 2025 factors. Not sure where you stand? The free SECR eligibility checker settles it in about 30 seconds.

What changed in the 2025 factors

The annual update follows a predictable pattern. The directions below are illustrative — confirm the exact figures in the official 2025 publication before relying on them.

The headline trend, and the most significant change year on year, is the continued fall in the UK grid electricity factor as more generation comes from renewables and energy efficiency improves. That steady decline in carbon intensity rewards genuine carbon reductions, but it also means a like-for-like year-on-year comparison needs the right factor year on both sides.

Where to download the 2025 factors

The factors are a free Excel download at gov.uk. You get five files:

• Full set — the comprehensive workbook for advanced users
• Condensed set — simplified for typical SECR users
• Flat file — one row per factor, for databases
• Methodology paper — how each factor is derived, and which variant to pick
• User guide

DEFRA also publishes prior-year factors going back 10+ years, so you can recalculate historical data on a consistent basis. A new set lands each year in late May or early June, so the timing is predictable.

How the factors are calculated

The UK Government compiles each emission factor from measured fuel chemistry, the UK electricity generation mix, transport efficiency data and IPCC global warming potentials, then publishes them with a methodology note. Most are expressed as carbon dioxide equivalent (CO2e, also written CO₂e) — a single metric that rolls up carbon dioxide, methane and nitrous oxide. You don't reproduce the calculation; you apply the published factor. The set spans the average carbon intensity of grid power through to specific freight movements, so almost any activity can be converted to carbon emissions.

How to apply the factors to SECR — four rules

Rule 1 — Match the factor year to the data year

The single most common SECR error. Data for calendar year 2025 uses the 2025 factors. For a financial year spanning two calendar years, apply one factor set consistently and document the choice. Because new factors arrive around June, an earlier accounts deadline may force you to use the previous year's set and restate next year — record that decision.

Rule 2 — Use the correct factor variant

Many sources offer several options. Nail down: natural gas — gross or net calorific value (UK utility bills are usually gross); UK electricity — generation only for scope 2 (T&D losses are scope 3 category 3); refrigerants — direct GWP only; diesel — average biofuel blend or 100% mineral.

Rule 3 — Match the unit

DEFRA factors are typically per kWh or per litre (fuels), per kWh (electricity), per kg (refrigerants), per km or passenger.km (transport), per m³ (water) and per tonne (waste). If your activity data is in different units (mpg, gallons, US tons), convert first, then sense-check against an order-of-magnitude expectation.

Rule 4 — Document the application

The audit trail must let an auditor reproduce your calculation. For each source, record the activity data and its source, the factor used and its reference (e.g. "DEFRA 2025, UK grid electricity"), the calculation, and the result in kgCO₂e and tCO₂e.

Worked example

A logistics group has the following 2025 activity data. Factors are illustrative — use the current published values.

These totals feed straight into the SECR report tables. Sanity-check your own figures with the free SECR carbon calculator, then build the disclosure with the SECR report generator.

Five common factor mistakes

1. Wrong year. Using 2025 factors for the previous year's data, or vice versa.
2. Gross/net confusion. Mixing gross and net calorific-value factors in one calculation.
3. Double-counting electricity. Adding scope 3 T&D losses into the scope 2 total — T&D belongs in scope 3 category 3 separately.
4. Outdated GWPs. Refrigerant calculations must use the GWP values DEFRA references for the year being applied.
5. Ignoring the methodology paper. Some factors carry application caveats — for example the air-travel radiative-forcing multiplier.

Annual refresh — what to expect

DEFRA and DESNZ publish a new set of conversion factors each year, so annual changes are predictable. The update typically lowers the UK grid electricity factor, refreshes biofuel content for road fuels, updates air-travel factors, adds or refines scope 3 categories, and keeps backward-compatible historical tables. Watch the gov.uk collection page each year for the latest conversion factors so your carbon accounting stays current.

How the DEFRA factors fit with other standards

For international operations — imported electricity outside the UK, for example — you'll need country-specific factors alongside the DEFRA set.

Get a specialist to apply the factors

Choosing and applying the right factors across a multi-source inventory is simple in theory and fiddly in execution: the wrong factor on a high-volume source can swing your SECR result by 10–20%. We don't file your report or sell software — we match you with a vetted, IEMA-qualified SECR specialist who can apply the 2025 emission factors across your full data set, get your carbon accounting right and document every choice. Check your eligibility and we'll connect you, free and with no obligation. You can also try the DEFRA factor explorer or read what SECR is.