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

The 2026 UK government emission factor for the average car (fuel unknown) is 0.26699 kg CO2e per mile, reported as Scope 1. That is 0.8% lower than the 2025 factor of 0.26915. Including well-to-tank, the full figure is 0.33778 kg CO2e per mile.

Updated 8 October 2026 by the Carbon Recycling team. Figures use the official UK government conversion factors and are checked against the current gov.uk guidance.

Work out your average car (fuel unknown) emissions

Miles in a year

= 2.67 tonnes CO2e in 2026 (Scope 1)3.38 tonnes including well-to-tank

Each mile × 0.26699 kg CO2e, the 2026 UK government (DESNZ) factor.

That is one line of your footprint. Want the whole thing done for you?

Carbon Recycling holds every UK government factor for every year, works out each line from your bills, mileage and travel, and writes your Carbon Reduction Plan and SECR report.

Start your 14-day free trial Try our free tools

No card needed for the trial.

Average car (fuel unknown) emission factor by year

Year	Scope 1 (kg CO2e per mile)	Well-to-tank	Full figure	Change
2026	0.26699	0.070790	0.33778	-0.8%
2025	0.26915	0.070790	0.33994	+0.2%
2024	0.26860	0.070790	0.33939	+0.2%
2023	0.26817	0.070270	0.33844	-2.4%
2022	0.27465	0.072550	0.34720	-0.5%
2021	0.27596	0.072550	0.34851	+0.0%
2020	0.27584	0.071100	0.34694	-3.2%
2019	0.28502	0.072790	0.35781	–

Total kg CO2e for the seven greenhouse gases, from the official DESNZ files for each year. 2026 factor ID: 4_301_3074_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 10,000 business miles a year. 10,000 miles × 0.26699 kg CO2e = 2.67 tonnes CO2e, reported as Scope 1. Adding well-to-tank brings the full figure to 3.38 tonnes CO2e; the extra 0.71 tonnes are Scope 3 category 3.

How to report it

Use this factor when you know how far a car went but not what fuel it uses, which is common for grey fleet mileage claims. It blends the UK car fleet's mix of petrol, diesel, hybrid and electric cars.

Cars the company owns or leases are Scope 1. Employees' own cars used on business (grey fleet) are Scope 3 business travel, category 6, using the same factor.

If your expenses system records the fuel type, the fuel-specific factors are more accurate.

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 diesel car: 0.27786 kg CO2e per mile
Average hybrid car: 0.20857 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.

Get your figures and reports done in an afternoon

Add a year of bills and Carbon Recycling produces your footprint, PPN 006 Carbon Reduction Plan and SECR report, with every figure traced to its government factor. Prices are on the pricing page, from £59 a month.

Start free trial See prices

14 days free. No card needed.