A car vs bike calculator is really four comparisons stacked on top of each other, and they do not all point the same way. Money and carbon dioxide usually favour the bike by a wide margin. Time almost always favours the car, sometimes by hours per week. Calories burned favours the bike, but it is the least reliable number on the page. A tool that reports only the first two is telling you half the story, which is why this one puts all four side by side and refuses to weight them for you.
Arb Digital publishes a free tools library built on the principle that a calculator should show its working. Every factor here is an editable input, because the honest answer to "how much CO2e does a car emit per mile" depends on the car, the fuel, the country and the year of the dataset. This page sits in the ecology section next to the flight carbon footprint calculator, which handles air travel with the same approach, and it deliberately overlaps as little as possible with the commute cost calculator, which prices a commute in money only and covers transit and rideshare modes this page does not.
What This Car vs Bike Calculator Does
It takes one commute — a one-way distance, a number of days a week and a number of weeks a year — and runs it twice. The car run prices fuel from your economy figure and fuel price, adds a per-mile allowance for everything else that wears out with mileage, and multiplies your chosen emission factor by the distance. The bike run charges a flat annual maintenance figure, emits nothing at the point of use, and converts riding hours into calories at a rate you set.
The headline is the difference in annual running cost. The four supporting figures are the carbon dioxide equivalent avoided in kilograms, the extra hours a year the bike costs you, the calories burned cycling across the year, and the total annual commute distance so you can sanity-check that the trip count is right. The two bars underneath show each mode's annual cost against the larger of the two.
How to Use It
- Enter the one-way distance and the trip pattern. The calculator doubles the one-way figure for the return leg automatically, so enter the distance to work, not the round trip. Days per week times weeks per year times two gives the number of legs.
- Set the car's real fuel economy. Use your trip computer's long-term average, not the window sticker. A short urban commute with a cold engine is the worst case for fuel economy, and the gap between label and reality is widest exactly here.
- Choose an emission factor and note where it came from. The default is the EPA's typical US passenger vehicle. If you are in the UK or EU, use the per-kilometre factor for your fuel and size class and convert it, then write down the year of the dataset.
- Be honest about the other cost per mile. This covers what mileage consumes: tyres, servicing, brakes and the depreciation that comes from distance rather than age. Leave insurance out unless dropping the commute would genuinely change your premium.
- Use door-to-door speeds, not moving speeds. Car time should include finding a parking space and walking from it. Cycling time should include locking up. This single correction is what turns a fantasy comparison into a usable one.
The Formula / How It's Calculated
Everything is converted to miles internally, then run through four short chains:
Annual distance = one-way distance × 2 × days per week × weeks per year. Car cost = (annual distance ÷ mpg × fuel price) + (annual distance × other cost per mile). CO2e avoided = annual distance × grams per mile ÷ 1,000. Extra hours = annual distance ÷ bike speed − annual distance ÷ car speed. Calories = annual distance ÷ bike speed × calories per hour.
Worked example using the values the page loads with. An 8-mile one-way commute, five days a week, 46 weeks a year is 8 × 2 × 5 × 46 = 3,680 miles a year. At 22.2 mpg that is 165.77 gallons; at 3.20 a gallon, 530.45 in fuel. Add 3,680 × 0.20 = 736.00 in other running costs and the car totals 1,266.45 a year. The bike costs 120, so the difference is 1,146.45. Emissions: 3,680 × 400 g = 1,472,000 g, or 1,472 kg CO2e avoided. Time: 3,680 ÷ 11 = 334.5 hours cycling against 3,680 ÷ 22 = 167.3 hours driving, so the bike costs 167.3 extra hours a year. Calories: 334.5 hours × 450 = 150,545 kcal.
Kilometres are multiplied by 0.621371 to reach miles before any of that happens, because the fuel economy and emission inputs are both per-mile quantities. Mixing a kilometre distance with a per-mile factor overstates the result by 61%, which is the most common arithmetic failure in transport footprint estimates.
Where the Emission Factor Comes From — and Why Yours Will Differ
The 400 grams per mile default is documented by the US Environmental Protection Agency in Greenhouse Gas Emissions from a Typical Passenger Vehicle, which builds it from two other published figures: every gallon of gasoline burned creates about 8,887 grams of CO2, and the average gasoline vehicle on the road achieves about 22.2 miles per gallon while covering roughly 11,500 miles a year. Those numbers multiply out to about 4.6 metric tons of CO2 a year, which is the figure that gets quoted in headlines.
Notice what that factor is and is not. It is a tailpipe figure, not a life-cycle figure, so it excludes extracting and refining the fuel and excludes manufacturing the car. It is also a fleet average spanning small hatchbacks and large pickups; a specific vehicle can sit at half or double it.
The other main published set is the UK's greenhouse gas reporting conversion factors 2025, issued by the Department for Energy Security and Net Zero on 10 June 2025. It publishes per-kilometre factors split by fuel type and vehicle size, and it separates the direct combustion factor from the well-to-tank factor so that reporters can choose whether upstream emissions are inside their boundary. Using a DESNZ well-to-wheel factor and an EPA tailpipe factor in the same comparison is a category error, and it is easy to make by accident when you take one number from one calculator and another from a different one.
A bicycle is not zero either, in the strict sense. Manufacturing a bike has a footprint, and so does the extra food a regular rider eats. Both are small relative to a car commute and both are outside this tool's boundary.
Time Is the Real Cost, and Most Comparisons Hide It
The default numbers produce a saving of over a thousand a year and a cost of 167 hours — roughly seven per hour. Whether that is a good trade depends on what your time is worth and on whether you value the riding time at zero, which most regular cyclists do not.
Two corrections change the picture more than people expect. The first is door-to-door speed. Average moving speed in a car on an urban commute is often quoted at 30 mph or more, but the trip also includes queuing, hunting for a space and walking from it. Measure the actual clock time from your front door to your desk and divide by the distance. The result is frequently in the low twenties, and in dense city centres it can fall below cycling speed entirely, at which point the extra-hours figure goes negative and the bike is faster.
The second is what the exercise displaces. If cycling to work replaces a gym session or a run you were doing anyway, the honest time cost is the extra hours minus the training time you no longer need. The tool cannot know that, so it reports the raw difference. Subtract the displaced time yourself before you judge the trade. The cycling calorie calculator is the better place to model the training side properly, and the time duration calculator helps if you are reconciling clock times across a week.
The Cost Per Mile You Are Probably Getting Wrong
There are two legitimate ways to cost a car mile and they differ by a factor of three. The average cost divides everything the car costs in a year — depreciation, insurance, tax, finance, servicing, fuel — by the miles driven. The marginal cost counts only what changes if you drive one more mile: fuel, tyres, a share of servicing, and mileage-driven depreciation.
For a commuting decision the marginal cost is the right one, because you keep the car either way. That is why the default other-cost input is 0.20 a mile rather than the much larger figures quoted in full ownership studies. If cycling would let you sell the car outright, the comparison changes completely: the whole of insurance, tax, finance and time-based depreciation moves into the car column, and the annual difference typically triples. The car depreciation calculator and the car insurance calculator are where you build that larger figure, and the cost per use calculator is a quick way to turn any annual total into a per-trip rate.
Being explicit about which of the two you used is what makes the result defensible. A comparison that quietly uses full ownership cost on the car side and marginal cost on the bike side will always favour the bike.
Calories Burned Is the Softest Number on This Page
Energy expenditure while cycling scales with rider mass, speed, wind, gradient, riding position and tyre choice. Doubling speed roughly quadruples aerodynamic drag, so a 15 mph commuter and an 11 mph commuter are not on the same curve. Published values for moderate cycling span a wide band, and any single figure is a midpoint of a distribution, not a measurement of you. That is why the rate is an input rather than a constant derived from your weight. Treat the annual total as an order of magnitude — useful for saying "roughly 150,000 kcal", useless for saying "150,545 kcal".
The intensity classification also matters if you are checking activity guidelines rather than energy balance. The US Centers for Disease Control and Prevention's Adult Activity: An Overview guidance describes leisurely cycling as moderate intensity and fast cycling as vigorous, with adults advised to accumulate 150 minutes of moderate or 75 minutes of vigorous activity a week. A commute of the length modelled here clears that on riding time alone, but the guidance is about minutes at an intensity, not about calories, and the two are not interchangeable.
Where This Comparison Breaks Down
Three situations make the arithmetic misleading. Mixed weeks: most people who switch do not switch every day, so run the tool at the number of days you would realistically ride. Trip chaining: if the drive also drops children at school or collects shopping, the bike does not replace the whole trip, and the distance to enter is only the part that genuinely disappears. Seasonality: riding eight months and driving four is 30 weeks, not 46.
A single commuter switching removes their own tailpipe emissions and nothing else. Claims about congestion, road wear or air quality operate at a population scale and cannot be attributed to one rider.
Arb Digital builds calculators and content that stand up to scrutiny — sourced, transparent about method, and fast enough to rank. Browse the free library, or tell us what you need.
Browse Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Entering the round-trip distance — the calculator already doubles the one-way figure, so entering 16 for an 8-mile commute doubles every result.
- Using the window-sticker fuel economy — short urban trips with a cold engine run well below the label figure, which understates the car's fuel cost and its emissions.
- Mixing a kilometre distance with a per-mile factor — that overstates the answer by 61%. Use the unit selector rather than converting in your head.
- Comparing full car ownership cost with marginal bike cost — pick average or marginal costing and apply the same basis to both modes, or the comparison means nothing.
- Using moving speed instead of door-to-door speed — parking, walking and locking up are part of the journey, and leaving them out is what makes driving look faster than it is.
Related Free Tools From Arb Digital
The commute cost calculator prices a commute across driving, transit and rideshare without touching emissions, while the fuel cost calculator handles a single journey's fuel spend and the MPG calculator works out your real fuel economy from tank fills. For air travel use the flight carbon footprint calculator, and for household resource use the electricity bill calculator. Everything else is in the free online tools hub.
Frequently Asked Questions
From the US Environmental Protection Agency's published figure for a typical American passenger vehicle. It is derived from about 8,887 grams of CO2 per gallon of gasoline burned and an average on-road fuel economy of about 22.2 miles per gallon. It is a tailpipe figure for an average vehicle, not a life-cycle figure for yours.
Usually not. For a commuting decision the relevant figure is the marginal cost of driving one more mile, and insurance and tax are paid whether or not you drive to work. They belong in the comparison only if cycling would let you sell the car entirely, in which case the annual difference roughly triples.
Because in dense urban traffic, once parking and walking are counted, door-to-door cycling speed can exceed door-to-door car speed. A negative value means the bike is the faster mode on the numbers you entered, not that the calculation has failed.
It is the softest figure on the page. Energy expenditure while cycling depends on rider mass, speed, wind, gradient and position, and published values span a wide band. Treat the annual total as an order of magnitude rather than a measurement, and replace the hourly rate with your own power or heart-rate data if you have it.
Not in a full life-cycle sense. Manufacturing the bike has a footprint, and a regular rider eats somewhat more food. Both are small relative to a car commute and both sit outside this tool's boundary, which reports emissions avoided at the point of use only.
Distance can be entered in kilometres and is converted to miles internally. Fuel economy and fuel price are per US gallon, so convert a litre price first, or convert an L/100 km figure to miles per gallon before entering it. The unit converter in the tools library will do both conversions.
Enter the number of days you would realistically ride rather than modelling a full switch. The days-per-week and weeks-per-year inputs exist precisely so that a three-day-a-week, eight-month pattern can be represented directly instead of being estimated afterwards.
This tool performs arithmetic on figures you supply. It is not financial, medical or transport advice, the calorie estimate is not a clinical measurement, and any emissions figure should be checked against the original published factor set and its year before it is reported anywhere that matters.
