Driving Emissions Calculator
Estimate the CO₂ a car trip or year of driving produces.
Results update as you type.
How it works
Every mile you drive in a petrol car burns fuel and releases carbon dioxide, and this driving emissions calculator turns your mileage and fuel economy into a clear CO₂ figure. Enter the miles driven, your car's miles per gallon, and the carbon per gallon of fuel, and it reports the kilograms of CO₂ produced for that distance. The calculation follows the fuel: distance divided by fuel economy gives gallons burned, and each gallon of gasoline releases about 8.89 kilograms of CO₂ according to the EPA. This means two levers control your emissions — how far you drive and how efficiently your car uses fuel. A thirsty vehicle covering long distances emits far more than an efficient one on the same route. You can use the tool for a single trip or a whole year by entering the relevant mileage. Seeing the number helps you compare vehicles, decide whether to combine errands, carpool, or shift to public transport, and understand how much a fuel-efficient or electric car would cut your footprint. Commuters weighing travel choices, drivers comparing cars, and anyone building a personal carbon budget use a driving emissions calculator to make transport decisions with real numbers. Because transport is one of the largest sources of household emissions, small changes in how and how much you drive add up over a year.
CO₂ (kg) = miles ÷ mpg × CO₂ per gallon
The carbon a car emits depends on how much fuel it burns, and fuel burned equals the distance driven divided by the vehicle's miles per gallon. Multiplying that gallon figure by the carbon dioxide released per gallon of gasoline — about 8.89 kilograms according to the EPA — gives total emissions. A more efficient car covers the same miles on fewer gallons, so a higher mpg directly lowers the CO₂ result, which is why fuel economy is the key lever for cutting driving emissions.
Source:U.S. EPA greenhouse gas equivalencies
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter miles driven, fuel economy and co₂ per gallon.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
CO₂ emitted updates instantly as you type — no button to press.
Frequently asked questions
Why is the CO₂ per gallon set to 8.89?
That is the U.S. EPA's figure for the carbon dioxide released by burning one gallon of gasoline, accounting for its carbon content and complete combustion. It is a well-established standard used across official emissions tools. Diesel differs slightly at about 10.18 kilograms per gallon because it is denser and more carbon-rich, so change the value if you drive a diesel vehicle to get an accurate result.
How do I find my car's fuel economy?
Your vehicle's manufacturer rating, on the window sticker or in the manual, gives official combined miles per gallon, but real-world economy is often lower. For accuracy, calculate it yourself: fill the tank, note the odometer, drive normally, then divide the miles covered by the gallons needed to refill. Using your actual measured mpg reflects your driving style, terrain, and conditions far better than the idealised laboratory figure.
Does this work for a whole year of driving?
Yes. Simply enter your total annual mileage instead of a single trip's distance, and the result becomes your yearly driving emissions. The average driver covers roughly 12,000 to 15,000 miles a year, so you can compare your figure against that benchmark. Entering annual mileage is the best way to see how driving fits into your overall carbon footprint alongside home energy and flights.
How do electric cars compare on this measure?
A pure electric car has no tailpipe emissions, so its direct driving CO₂ here is effectively zero. However, it is not truly zero-carbon because the electricity used to charge it may come from fossil fuels. To compare fairly, estimate the emissions of the grid electricity the EV consumes. On a clean grid an electric car is dramatically lower carbon than petrol; on a coal-heavy grid the gap narrows but usually still favours the EV.
What is the easiest way to cut my driving emissions?
The two direct levers are driving fewer miles and burning less fuel per mile. Combining trips, carpooling, working from home, and choosing walking, cycling, or public transport for short journeys all reduce mileage. Keeping tyres inflated, removing roof racks, driving smoothly, and maintaining your engine improve fuel economy. When replacing a car, choosing a more efficient or electric model delivers the largest lasting reduction in the numbers shown here.