How this instrument works
Comparing a car trip to a bike trip on tailpipe emissions alone understates the car's footprint and overstates the bike's — a bicycle has no tailpipe, but manufacturing it still costs carbon, and the rider needs extra food energy to power the ride, which itself has a footprint. A fair comparison has to count the full life cycle on both sides: vehicle manufacture, fuel or electricity, and for cycling, that extra metabolised food energy.
The European Cyclists' Federation's 2011 report 'Quantifying CO2 savings of cycling' did exactly that, arriving at roughly 271 grams of CO2-equivalent per passenger-kilometre for an average car and about 21 grams CO2e per kilometre for cycling — both figures drawn from the same study, so the comparison is apples-to-apples rather than mixing sources with different assumptions.
This calculator multiplies those per-kilometre figures by your actual trip distance and frequency, so instead of an abstract 'cycling is greener' statement, you get a concrete kilogram figure for exactly how much CO2e your own commute or errand pattern saves by choosing the bike.
- Enter One-way trip distance — the length of a single leg of your trip, in km.
- Enter Round trips per week — how many times a week you make this trip and back.
- Enter Number of weeks — the period to total, such as 52 for a full year.
- Adjust Car footprint and Bicycle footprint if you have more specific per-km figures.
- Read CO2e saved by biking instead of driving — the total kilograms avoided over the period.
Worked example — a 10 km commute, five days a week, for a year
Using the ECF's life-cycle figures (271 g CO2e/km for a car, 21 g CO2e/km for a bike), a 10 km one-way commute made as a round trip 5 times a week for 52 weeks covers 10 × 5 × 52 = 2,600 trip-kilometres over the year.
By car, that's 2,600 × 271 ÷ 1000 = 704.6 kg CO2e for the year. By bike, it's 2,600 × 21 ÷ 1000 = 54.6 kg CO2e — a difference of 650.0 kg CO2e saved by cycling the commute instead of driving it, roughly the same as the emissions from burning about 73 gallons of gasoline.
Questions
Why does a bicycle have a carbon footprint at all if it has no engine?
Two reasons: manufacturing the bicycle itself — mining and shaping the metal frame, producing tyres and components — carries an upfront carbon cost, and riding it burns extra calories that the cyclist has to replace with food, which itself has a production and supply-chain footprint. The ECF's 21 g CO2e/km figure folds both of those in, which is why it isn't zero even though there's no fuel being burned during the ride.
Does the car figure include manufacturing the car, or just the fuel?
It includes both — the ECF's 271 g CO2e/km is a full life-cycle figure covering fuel or electricity burned per kilometre plus the vehicle's manufacturing footprint amortised over its expected lifetime distance. That's why it's higher than a simple tailpipe-emissions-only number would suggest, and why it's directly comparable to the bicycle figure, which is built the same way.
Do these figures apply to electric cars too?
Not directly — the ECF's 271 g CO2e/km average reflects the mostly-petrol and diesel European vehicle fleet as of 2011, and an EV's per-km footprint depends heavily on the carbon intensity of the electricity grid charging it, which varies enormously by country and has generally improved since 2011. If you're comparing against an EV specifically, adjust the car footprint input to a figure that reflects your local grid rather than relying on the default.
How much does trip distance change the comparison?
It scales both totals proportionally, so the relative savings percentage stays the same regardless of distance — cycling always saves about 92% of the car's CO2e per kilometre at these default figures (21 is roughly 8% of 271). What changes with distance is the absolute kilogram figure: a longer commute means both bigger totals and a bigger absolute gap between them.
Is this a realistic comparison for every car and every cyclist?
It's a population-average comparison, not a prediction for any one specific vehicle or rider — actual footprints vary with car size and fuel type, how efficiently a cyclist's diet converts into pedalling energy, and regional manufacturing practices. Both the car and bicycle inputs are adjustable specifically so you can substitute a more specific figure, such as your own vehicle's published emissions rating, if you have one.