DEFRA 2024 Emission Factors: What Changed and Why It Matters

What Are DEFRA Emission Factors?

Every year, the UK Department for Environment, Food & Rural Affairs (DEFRA), in partnership with the Department for Energy Security and Net Zero (DESNZ), publishes a comprehensive set of greenhouse gas conversion factors. These factors allow businesses to convert activity data — such as litres of fuel used, kilowatt-hours of electricity consumed, or kilometres travelled — into carbon dioxide equivalent (CO2e) emissions.

The DEFRA conversion factors are the standard reference for UK company reporting. If you are creating a carbon reduction plan, submitting data for SECR (Streamlined Energy and Carbon Reporting), or calculating your carbon footprint for any UK-focused purpose, DEFRA factors are what you should be using.

The full dataset, officially titled "UK Government GHG Conversion Factors for Company Reporting", is published as an Excel workbook containing thousands of individual factors across dozens of categories.

Why Factors Change Each Year

Emission factors are not fixed constants. They change annually because the underlying reality changes. The UK electricity grid, for example, becomes less carbon-intensive each year as more renewable generation comes online. In 2015, the grid electricity factor was approximately 0.46 kg CO2e per kWh. By 2024, it had fallen to approximately 0.21 kg CO2e per kWh — a reduction of more than 50% in less than a decade.

Other factors that drive annual changes include:

• Grid decarbonisation — as coal plants close and wind/solar capacity grows, the electricity factor drops
• Vehicle fleet updates — as average vehicle efficiency improves and EVs increase market share, transport factors shift
• Waste management improvements — changes in UK recycling rates and landfill diversion affect waste factors
• Fuel composition changes — the introduction of E10 petrol (containing 10% bioethanol) reduced the petrol emission factor
• Improved data collection — better measurement and reporting across industries refines factor accuracy

Key Changes in the 2024 Update

The 2024 edition of the DEFRA factors introduced several notable changes that affect carbon reduction plan calculations:

Electricity Factor Reduction

The UK grid electricity factor continued its downward trend, reflecting the ongoing expansion of offshore wind capacity and the retirement of remaining coal-fired generation. This means that businesses with high electricity consumption will see a lower calculated footprint compared to previous years, even if their actual consumption has not changed.

This is important context for year-on-year comparisons. A reduction in your calculated electricity emissions may reflect grid decarbonisation rather than any action your business has taken. Good carbon reporting distinguishes between these two effects.

Transport Factor Updates

Vehicle emission factors were updated to reflect the changing composition of the UK vehicle fleet. With increasing EV adoption, the average emission factor for "unknown vehicle" categories has decreased slightly. Specific factors for petrol, diesel, and hybrid vehicles were also adjusted based on updated real-world driving data.

The factors for rail travel were updated to reflect both improvements in rolling stock efficiency and changes in average passenger loading. For businesses that report business travel by rail, this affects both absolute figures and comparisons with road and air alternatives.

Well-to-Tank Factors

DEFRA provides both direct (combustion) factors and well-to-tank (WTT) factors. WTT factors account for emissions from extracting, refining, and transporting fuels before they are used. The 2024 update refined several WTT factors, particularly for natural gas and transport fuels. A complete carbon footprint should include both direct and WTT emissions — something that many basic calculators miss.

How This Affects Your Carbon Reduction Plan

If your carbon reduction plan was calculated using 2023 or earlier factors, the absolute numbers will differ from a 2024 calculation even if your underlying activity data is identical. This does not mean your old plan is wrong — it was correct for the factors available at the time. However, for new plans and annual updates, using the latest factors ensures accuracy and credibility.

Key implications:

• Baseline recalculation — if you are updating your CRP, consider whether to recalculate your baseline year using 2024 factors for consistency
• Target tracking — year-on-year comparisons should use consistent factors or clearly note which factor set was used
• Procurement compliance — government buyers expect current factors to be used in new submissions
• Credibility — using outdated factors undermines the credibility of your reporting

Using the Right Factors

Every Carbonhogs plan is calculated using the latest DEFRA 2024 emission factors. We update our calculation engine each year when new factors are published, so you can be confident that your plan reflects the most current and accurate conversion factors available.

If you are unsure which factors your existing plan uses, or if you need an updated calculation, our questionnaire takes about ten minutes to complete and produces a fully compliant carbon reduction plan instantly.