Small car: carbon footprint per km
Live factor value
0.14282 kgCO2e per km
Source: UK DESNZ greenhouse-gas conversion factors, 2026 (revision 2). Factor set desnz-2026-r2.
A small car (supermini class and below in the official definitions) emits about 14% less per kilometre than the UK average car — the live DESNZ 2026 figure is below — and roughly 40% less than a large car or SUV covering the same ground.
Size is the honest lever hiding in plain sight: at typical UK mileage the small-versus-large gap is worth several hundred kilograms of CO2e a year, more than most people save through any amount of eco-driving technique. Our travel and commuting calculators let you pick the size band so the difference shows up line by line.
Worked example
Typical UK annual mileage (~10,000 km): 10,000 × 0.14282 = 1,428 kgCO2e.
Measure your own with the free travel calculator.
Frequently asked questions
- How much does car size matter?
- On the DESNZ 2026 unknown-fuel figures, a small car emits ~14% less per km than the average car and roughly 40% less than a large one — several hundred kg CO2e a year at normal mileage.