Car vs. Bike Calculator

Compare the CO2 emissions and fuel cost of driving vs. biking a trip, and see your weekly and yearly savings from switching.

Quick Facts

Method
EPA gasoline emissions factor: 8,887 g CO2 per gallon burned
Car CO2 = (distance ÷ MPG) × 8,887 g. Biking is treated as a zero-tailpipe-emission substitute for the same trip.

Your Results

Calculated
CO2 saved per week
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By biking instead of driving
CO2 saved per year
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Based on 52 weeks
Fuel cost saved per week
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Gasoline not purchased
Fuel cost saved per year
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Based on 52 weeks

Ready

Enter your trip details and click Calculate.

Frequently Asked Questions

What formula does this calculator use?
It converts your driving distance into gallons of gasoline burned (miles ÷ MPG), then applies the EPA's emissions factor of 8,887 grams of CO2 per gallon of gasoline combusted. Biking the same distance is treated as producing zero tailpipe CO2, so the full amount is counted as "saved" when you choose the bike instead of the car. Fuel cost savings are calculated as gallons not burned × your local gas price.
Why 8,887 grams of CO2 per gallon of gasoline?
This is the EPA's standard emissions factor for motor gasoline, based on the carbon content of the fuel (a gallon of gasoline weighs about 6.3 lb and is roughly 87% carbon by mass, which oxidizes fully to CO2 when burned). It's the same constant the EPA uses in its "Greenhouse Gas Emissions from a Typical Passenger Vehicle" reference and is the standard used across most car-emissions calculators.
Does this account for the bike's own emissions?
This calculator counts direct (tailpipe) emissions only, which is the standard, most-cited comparison and is why the bike side of the equation is zero. A full lifecycle comparison would also include the manufacturing footprint of the car and bike and the emissions from producing the extra food a cyclist eats to fuel the ride — commonly estimated at roughly 15-40 g CO2e per mile depending on diet, far below a car's 300-450+ g CO2e per mile, but not literally zero. For a simple "should I drive or bike this trip" decision, tailpipe-only is the standard and most useful comparison.
How accurate is the default 25 MPG?
25 MPG is close to the EPA's reported average fuel economy for the U.S. light-duty vehicle fleet (new passenger cars and light trucks combined average is roughly in the low-to-mid 20s to low 30s depending on model year). Replace it with your own vehicle's combined MPG rating (found on its window sticker or fueleconomy.gov) for a result specific to your car.

The formula: converting miles driven into CO2 emitted

Every gallon of gasoline burned in a car engine releases about 8,887 grams (19.6 lb) of CO2 into the atmosphere, regardless of the vehicle — this comes directly from the carbon content of the fuel itself, per the EPA. To find the CO2 from a trip, this calculator first converts distance into fuel burned: gallons = miles ÷ MPG, then multiplies by the emissions factor: CO2 (g) = gallons × 8,887. A bike ride covering the identical distance is counted as zero tailpipe emissions, so that full amount becomes your savings from choosing to pedal instead of drive.

Why this matters: transportation is a major emissions source

Transportation is the largest source of U.S. greenhouse gas emissions, and light-duty vehicles (cars, SUVs, pickups) make up the majority of that share. Short trips are disproportionately wasteful: a cold engine runs less efficiently for the first mile or two, so a car's real-world grams-per-mile on a 2-3 mile commute is often worse than its rated average. Because roughly half of all car trips in the U.S. are under three miles — well within comfortable biking or e-biking range — the potential emissions savings from mode-shifting short trips is large relative to the effort involved.

Reference points for common vehicles and trip lengths

A typical gasoline sedan (around 30 MPG) emits about 296 g CO2 per mile; a typical SUV or pickup (around 20 MPG) emits about 444 g CO2 per mile. At the EPA's fleet-average fuel economy of roughly 25 MPG, that works out to about 356 g (0.78 lb) of CO2 per mile driven. A 4-mile round-trip commute (8 miles total) made 5 days a week therefore produces on the order of 31 lb of CO2 weekly from driving alone — the same trip by bike produces none.

What the numbers don't capture

This calculator compares tailpipe emissions and fuel spend only — it doesn't include the embodied carbon of manufacturing a car or a bike, road wear, or the marginal calories a cyclist burns and later eats to replace. It also doesn't account for time, weather, safety, or cargo-carrying needs, all of which are legitimate reasons a car may still be the right choice for a given trip. Use the dollar and CO2 figures as one input among several, not the only one.

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