Calculate the estimated CO2 emissions from your driving, based on distance traveled, fuel consumption rate, and fuel type.
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Every liter of petrol or diesel burned in a car's engine releases a predictable amount of carbon dioxide (CO2), since the carbon contained in the fuel combines with oxygen during combustion in a fixed, well-understood chemical ratio. This calculator estimates the CO2 emissions from your driving by multiplying the amount of fuel your trip or annual driving would use — calculated from the distance traveled and your car's fuel consumption rate — by a standard emission factor for the fuel type: roughly 2.31 kg of CO2 per liter of petrol, or 2.68 kg per liter of diesel, since diesel is denser and carbon-richer per liter even though diesel engines often use less fuel for the same distance. The result includes both a total figure for the distance entered and a standardized grams-of-CO2-per-kilometer (g CO2/km) rate, the same style of metric used in official vehicle emissions ratings, which makes it easy to compare against other cars or published figures. This calculator estimates only tailpipe combustion emissions, not the broader lifecycle emissions from producing and transporting the fuel itself.
Every time an internal combustion engine burns fuel, it converts the carbon stored in that fuel into carbon dioxide (CO2) through a chemical reaction with oxygen from the air. Unlike many aspects of a car's performance, this particular reaction is remarkably predictable: for a given fuel type, the amount of CO2 released depends almost entirely on how much fuel was actually burned, not on the engine, the driving style, or the vehicle model. That predictability is what makes it possible to estimate a trip's or a car's carbon footprint from just two numbers — distance driven and fuel consumption rate — without needing any information about the specific engine involved.
The conversion itself relies on standard emission factors that chemists and regulators have established for each common fuel type. Petrol (gasoline) releases approximately 2.31 kilograms of CO2 for every liter burned, while diesel releases about 2.68 kilograms per liter — a meaningfully higher figure, because diesel fuel is denser and contains more carbon atoms packed into each liter. This is why comparing two cars purely by liters of fuel used can be misleading if they run on different fuel types: a diesel car burning fewer liters than a petrol car over the same distance might still produce a similar, or even higher, total CO2 figure, depending on exactly how much less fuel it used.
Multiplying the emission factor by the fuel consumed per kilometer produces a standardized metric — grams of CO2 per kilometer (g CO2/km) — which is the same style of figure used in official vehicle emissions labeling and fuel economy comparisons around the world. Typical passenger cars on the road today commonly fall somewhere between roughly 120 and 200 g CO2/km, with smaller and more fuel-efficient vehicles toward the lower end of that range and larger vehicles or older, less efficient engines toward the higher end. Expressing the result this way makes it straightforward to compare a specific car's real-world driving against manufacturer-published figures or against other vehicles being considered.
It's worth being clear about what this kind of calculation does and doesn't capture. It measures only tailpipe emissions — the CO2 released directly from burning fuel in the engine — and doesn't account for the additional emissions generated earlier in the fuel's life cycle, including crude oil extraction, refining into petrol or diesel, and transportation to the pump. A full lifecycle analysis, which some more detailed carbon-footprint tools attempt, typically reports meaningfully higher total figures once those upstream emissions are included. This calculator also doesn't apply to electric vehicles, whose emissions depend entirely on how the electricity used to charge them was generated, which varies enormously by region and power grid.
Practically, this kind of estimate is useful in a few common situations: understanding the rough carbon footprint of a specific road trip, comparing the emissions implications of two different cars or fuel types before a purchase decision, or estimating an annual driving footprint by entering a yearly mileage figure instead of a single trip's distance. Because real-world fuel consumption varies with traffic, terrain, driving style, and weather, the most accurate results come from using a fuel consumption rate measured from your own vehicle's actual recent driving rather than a manufacturer's official rating, which is typically measured under standardized laboratory conditions that don't always match everyday driving.
CO2 emissions are calculated by multiplying the amount of fuel burned (in liters) by a standard emission factor for that fuel type — roughly 2.31 kg CO2 per liter of petrol (gasoline) or 2.68 kg CO2 per liter of diesel — since burning a fixed amount of fuel of a given type always releases essentially the same amount of carbon dioxide.
Diesel fuel is denser and contains more carbon atoms per liter than petrol, so burning one liter of diesel releases more CO2 than burning one liter of petrol — even though diesel engines are often more fuel-efficient overall (using fewer liters for the same distance), which can partly offset the difference.
It varies by vehicle and fuel type, but many modern cars fall somewhere in the range of roughly 120 to 200 g CO2/km, with smaller, more efficient cars near the lower end and larger vehicles or older engines near the higher end.
No. This calculator only estimates tailpipe emissions from burning the fuel, based on standard combustion emission factors — it doesn't include the additional emissions from extracting, refining, and transporting the fuel before it reaches your tank, which is why more comprehensive lifecycle analyses often report somewhat higher total figures.
Yes — enter your typical annual distance instead of a single trip's distance, along with your car's usual fuel consumption rate, to get an estimated yearly CO2 figure; just keep in mind that real-world fuel consumption can vary with driving conditions, so treat the result as a reasonable estimate rather than an exact figure.