Car Carbon Emissions Calculator
Calculate the annual CO₂ emissions from your car based on how far you drive, your fuel type, and the mix of city versus highway driving. Useful for comparing vehicles or planning emission reductions.
Last updated: September 2026
Formula below · 2 sources (epa.gov, Wikipedia) · Updated Sep 2026
Compare with similar
About this calculator
Vehicle CO₂ emissions depend on how much fuel is burned and the carbon intensity of that fuel. The formula used here is: CO₂ (lbs/year) = (milesPerYear / fuelEfficiency) × fuelEmissionFactor × (1 + (cityPercent / 100 − 0.5) × 0.2). Dividing annual miles by fuel efficiency (mpg) gives gallons consumed per year. Each gallon is then multiplied by the fuel-specific emission factor — roughly 19.6 lbs for regular gasoline, 22.4 lbs for diesel and about 13.7 lbs for E85 (85% ethanol at 12.7 lbs/gal plus 15% gasoline; tailpipe CO₂ including the biogenic share — E85 also gives fewer miles per gallon). The final term adjusts for driving conditions: city driving involves more idling and acceleration, lowering real-world fuel economy by up to 10% compared to highway driving. This correction factor shifts the result up or down by ±10% as city percentage moves from 0% to 100%.
How to use
Imagine you drive 15,000 miles per year in a gasoline car (emission factor 19.6 lbs/gallon) that gets 28 mpg, with 60% city driving. Step 1 — Gallons used: 15,000 / 28 = 535.7 gallons. Step 2 — City driving adjustment: 1 + (60/100 − 0.5) × 0.2 = 1 + 0.1 × 0.2 = 1.02. Step 3 — Total CO₂: 535.7 × 19.6 × 1.02 ≈ 10,710 lbs (≈4.9 metric tons) of CO₂ per year. Compare this with a 40-mpg hybrid doing the same miles: 15,000/40 × 19.6 × 1.02 ≈ 7,497 lbs — a saving of over 3,200 lbs annually.
Frequently asked questions
How many pounds of CO₂ does a car emit per mile on average?
At 28 mpg a gasoline car emits about 19.6 ÷ 28 = 0.70 lbs of CO₂ per mile; the EPA figure for a typical US passenger vehicle is about 400 g (0.89 lbs) per mile. Larger SUVs or trucks averaging 18 mpg exceed 1.0 lb/mile, while 50-mpg hybrids drop to about 0.40 lbs/mile. Electric vehicles produce zero tailpipe emissions, though upstream grid emissions still apply.
Does city driving versus highway driving significantly change carbon emissions?
Yes — city driving involves frequent braking and acceleration, which increases fuel consumption by roughly 10–20% compared to steady highway speeds. This calculator applies a ±10% adjustment based on your city driving percentage. For a driver covering 15,000 miles entirely in city conditions versus entirely on the highway, the difference in annual CO₂ can exceed 1,000 lbs.
How does diesel compare to gasoline in terms of CO₂ emissions per mile?
Diesel contains more carbon per gallon (~22.4 lbs CO₂ vs. ~19.6 lbs for gasoline), but diesel engines are typically 20–30% more fuel-efficient. The net result is that a diesel vehicle often emits slightly less CO₂ per mile than a comparable gasoline model, despite the higher per-gallon emission factor. However, diesel also produces higher levels of nitrogen oxides and particulates, which carry separate air-quality concerns.