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How to use the Car CO₂ Emissions Calculator
- 1Enter how far you drive and choose per week, month or year.
- 2Pick your type of car, or enter your exact fuel economy.
- 3See your yearly CO₂, the trees needed to absorb it, and how other cars compare.
How car emissions are calculated
We use the UK Government's official greenhouse gas conversion factors (DESNZ/DEFRA 2026), which companies use for carbon reporting: an average petrol car emits about 162 g CO₂e per km, an average diesel about 173 g, a hybrid about 130 g, and an electric car about 30 g including UK charging electricity.
If you enter your own fuel economy, we multiply the fuel you burn by its carbon content: about 2.08 kg CO₂e per litre of petrol and 2.51 kg per litre of diesel. For electric cars, emissions depend on how clean your electricity grid is.
Is an electric car really cleaner?
Yes, over its lifetime in almost every country. EVs have higher emissions from battery manufacturing, but much lower emissions while driving. On a clean grid like France's an EV emits a fraction of a petrol car's CO₂; even on coal-heavy grids most studies find EVs come out ahead over the car's life.
Easy ways to cut car emissions
- Keep tyres at the right pressure: under-inflated tyres raise fuel use by a few percent.
- Drive smoothly and stay near the speed limit; fuel use climbs fast above about 100 km/h (60 mph).
- Remove roof boxes and racks when you are not using them.
- Combine short trips: a cold engine uses much more fuel for the first few kilometres.
- Share rides or switch one weekly commute to public transport or cycling.
Frequently asked questions
How much CO2 does a car emit per year?
An average petrol car driven 12,000 miles (19,300 km) emits about 3.1 tonnes of CO₂e per year. Large SUVs can emit over 5 tonnes; an electric car on the UK grid emits about 0.6 tonnes.
How many trees offset a car?
A mature tree absorbs roughly 22 kg of CO₂ per year, so offsetting 3 tonnes takes about 140 trees for a year. Driving less and switching to cleaner cars cuts emissions far faster.