Average diesel car emission factor 2026 (UK, kg CO2e per mile)

The 2026 UK government emission factor for average diesel car is 0.27786 kg CO2e per mile, reported as Scope 1. That is 0.2% lower than the 2025 factor of 0.27849. Including well-to-tank, the full figure is 0.34459 kg CO2e per mile.

Updated 3 October 2026 by the Carbon Recycling team. Figures use the official UK government conversion factors and are checked against the current gov.uk guidance.

Average diesel car emission factor by year

Year	Scope 1 (kg CO2e per mile)	Well-to-tank	Full figure	Change
2026	0.27786	0.066730	0.34459	-0.2%
2025	0.27849	0.066730	0.34522	+1.9%
2024	0.27334	0.066730	0.34007	+0.0%
2023	0.27332	0.066700	0.34002	-0.6%
2022	0.27492	0.066040	0.34096	+1.4%
2021	0.27108	0.066040	0.33712	0.0%
2020	0.27108	0.065160	0.33624	-2.8%
2019	0.27901	0.066550	0.34556	–

Total kg CO2e for the seven greenhouse gases, from the official DESNZ files for each year. 2026 factor ID: 4_301_3069_9_1. Where a factor jumps sharply between two years, it is usually because DESNZ changed its method or data source, not because the activity itself changed.

Worked example

Take one company car driven 15,000 business miles a year. 15,000 miles × 0.27786 kg CO2e = 4.17 tonnes CO2e, reported as Scope 1. Adding well-to-tank brings the full figure to 5.17 tonnes CO2e; the extra 1.00 tonnes are Scope 3 category 3.

How to report it

Use this factor when you know the distance but not the fuel bought. For a car the company owns or leases it is Scope 1. For an employee's own car used on business, often called grey fleet, the same factor is Scope 3 business travel.

If you know the car's size, the small, medium and large car factors are more accurate than the average.

Where the data comes from

You'll usually find it in mileage logs, expenses claims or telematics, in miles. Keep the source documents: anyone checking your Carbon Reduction Plan or SECR report may ask how each figure was worked out.

Read more about how the factors change each year in our guide to the 2026 conversion factors, or see how we apply them in our methodology.

Related emission factors

Average petrol car: 0.25993 kg CO2e per mile
Average hybrid car: 0.20857 kg CO2e per mile
Average battery electric car: 0.043220 kg CO2e per mile
All UK emission factors

Frequently asked questions

Which year's factor should I use?

The set for the year your reporting period falls in. If your financial year spans two calendar years, use the set for the calendar year most of it falls in, and keep the same rule every year. Don't restate past years with new factors unless you are correcting an error.

Is this the DEFRA factor?

Yes. The UK government conversion factors used to be published by DEFRA, then BEIS, and since 2023 by the Department for Energy Security and Net Zero (DESNZ). Many people still call them the DEFRA factors.

Do I need to include well-to-tank emissions?

They are Scope 3 category 3 (fuel- and energy-related activities). SECR doesn't require them, and PPN 006 doesn't list category 3 among its required Scope 3 categories, but including them gives a more complete footprint and some customers ask for them.

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