Travel · emission factor
The Carbon Footprint of a Petrol Car
231 g CO₂e / km
Driving a typical petrol car emits about 231 g CO₂e per passenger-kilometre, based on European Environment Agency and IPCC data. That makes it one of the most carbon-intensive everyday ways to travel — more than ten times the footprint of a train journey and nearly on par with flying per kilometre.
Why petrol cars emit so much
Burning one litre of petrol releases roughly 2.3 kg of CO₂, and combustion engines convert only a fraction of that fuel energy into motion — much of it is lost as heat. The 231 g figure also reflects a crucial real-world detail: occupancy. Most car trips carry just one person, often around 1.5 occupants on average, so the whole vehicle's exhaust is attributed to very few passengers. Add cold starts, stop-and-go urban traffic, air conditioning, and tyre and brake wear, and the per-kilometre footprint climbs well above what laboratory fuel-economy ratings suggest. Road transport is a major climate lever: transport accounts for roughly a fifth of global energy-related CO₂ emissions, and passenger cars are the largest slice of that.
How 231 g/km compares to other transport
Per passenger-kilometre, a petrol car (231 g) sits just below a plane (255 g) and a cruise ship (280 g), and above a diesel car (192 g). Shared and electrified modes are in a different league: a bus averages about 105 g, a train around 20 g on a low-carbon grid, and an electric car roughly 8 g — a figure that mostly reflects tyre and brake wear when charged on clean electricity. Cycling and walking are effectively zero. Concretely, a 10 km daily commute by petrol car produces about 2.3 kg CO₂e each way; the same trip by train is around 200 g, and by bike, none at all.
What actually moves the needle
The biggest gains come from driving fewer solo kilometres, not from marginal efficiency tweaks. Carpooling immediately divides the footprint: two people in the same car halves the per-passenger figure to about 115 g/km, already close to a bus. Driving style matters too — smooth acceleration, moderate motorway speeds, and properly inflated tyres can cut fuel use by 10–20%. For those replacing a vehicle, switching to an electric car on a reasonably clean grid reduces per-kilometre emissions by more than an order of magnitude, even after accounting for battery manufacturing over the car's lifetime. And for short urban trips, where cold engines are least efficient, walking or cycling replaces the most carbon-intensive kilometres a petrol car drives.
How petrol car compares
g CO₂e / km · data as used in the Decarbonr app · sources: European Environment Agency, IPCC
How to reduce this footprint
- ✓ Carpool when you can — two occupants halve the per-person footprint from 231 g to about 115 g per km.
- ✓ Swap short urban trips (under 5 km) for cycling or walking, where cold engines burn fuel least efficiently.
- ✓ Drive smoothly, keep tyres properly inflated, and ease off motorway speeds to trim fuel use by 10–20%.
- ✓ Log your regular trips in a tracker like Decarbonr to see which journeys dominate your footprint and which are easiest to shift to train or bus.
Frequently asked questions
How much CO₂ does a petrol car emit per km?
A typical petrol car emits about 231 g CO₂e per passenger-kilometre, based on EEA and IPCC data. This real-world figure accounts for average occupancy and driving conditions, so it is higher than manufacturer fuel-economy ratings suggest.
Is driving a petrol car worse than flying?
Per passenger-kilometre they are surprisingly close: 231 g for a petrol car versus about 255 g for a plane. Flights are usually worse in total because they cover far greater distances in one trip, but a solo long-distance drive can rival a flight's per-km footprint.
How much better is an electric car than a petrol car?
On a clean electricity grid, an electric car emits around 8 g CO₂e per km — mostly from tyre and brake wear — versus 231 g for petrol, roughly a 96% reduction per kilometre. Even including battery manufacturing, an EV typically repays its production emissions within a couple of years of driving.
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Sources & methodology: see Research & scientific references. Figures are averages used by the Decarbonr app; real-world values vary by production system, country, and occupancy.