Vehicle Emissions Calculator
Calculate your car's annual CO₂ output using driving distance, fuel efficiency, fuel type, and the share of city versus highway driving. Use it to compare vehicles or assess your personal transport footprint.
Last updated: September 2026
Formula below · 2 sources (epa.gov, Wikipedia) · Updated Sep 2026
Compare with similar
About this calculator
A vehicle's CO₂ emissions depend on how much fuel it burns and how carbon-dense that fuel is. The formula is: Annual CO₂ (lbs) = (distance / fuelEfficiency) × fuelFactor × (1 + (cityPercent / 100) × 0.15). First, distance divided by fuelEfficiency (MPG) gives gallons of fuel consumed per year. That volume is multiplied by the fuelFactor in lbs CO₂ per gallon: gasoline 19.6 (EPA: 8,887 g), diesel 22.4 (10,180 g) and E85 about 13.7 including the biogenic CO₂ from ethanol. For an electric car enter its MPGe rating: one gallon-equivalent is 33.7 kWh, which on the US-average grid (0.77 lbs/kWh, EPA eGRID2023) is about 25.9 lbs CO₂. Diesel produces more CO₂ per gallon but often delivers better fuel economy, so net annual emissions can be similar. The city driving adjustment (1 + cityPercent/100 × 0.15) adds up to 15% extra emissions at 100% city driving, reflecting stop-start inefficiency and idling losses. The final result is annual CO₂ in pounds.
How to use
Suppose you drive 12,000 miles/year in a gasoline car (19.6 lbs CO₂/gallon) getting 30 MPG, with 40% city driving. Step 1 — Fuel consumed: 12,000 / 30 = 400 gallons. Step 2 — Base CO₂: 400 × 19.6 = 7,840 lbs. Step 3 — City driving adjustment: 1 + (40/100) × 0.15 = 1 + 0.06 = 1.06. Step 4 — Final emissions: 7,840 × 1.06 = 8,310 lbs CO₂ per year, about 3.8 metric tons. A diesel car achieving 40 MPG on the same route would emit (12,000/40) × 22.4 × 1.06 = 7,123 lbs — about 14% less despite higher per-gallon CO₂. An EV rated 110 MPGe would emit about (12,000/110) × 25.9 × 1.06 ≈ 2,995 lbs on the average US grid.
Frequently asked questions
Why does city driving increase vehicle CO₂ emissions compared to highway driving?
City driving involves frequent acceleration, braking, and idling — all of which increase fuel consumption without covering proportional distance. Internal combustion engines operate least efficiently at low speeds and high load transients, so stop-and-go traffic burns significantly more fuel per mile than steady highway cruising. The calculator captures this with a 15% maximum penalty applied proportionally to your city driving share. Hybrid vehicles partially offset this penalty by recovering braking energy, which is why they often show the largest efficiency advantage precisely in city conditions. Reducing city driving or switching to a hybrid can meaningfully cut your annual CO₂ output.
What is the difference in CO₂ emissions between petrol and diesel vehicles per mile driven?
Diesel fuel contains more carbon atoms per litre than petrol, producing 2.68 kg CO₂ per litre compared to 2.31 kg for petrol — about 16% more per unit of fuel burned. However, diesel engines are typically 20–35% more fuel-efficient, meaning they travel more miles per litre. The net effect is that a well-matched diesel car often emits 10–15% less CO₂ per mile than its petrol equivalent. The trade-off is that diesel combustion produces higher levels of nitrogen oxides and particulates, which harm local air quality. From a pure CO₂ perspective, diesel remains marginally cleaner per mile, but electrification outperforms both significantly.
How do I use a vehicle emissions calculator to compare two cars before buying?
Enter your expected annual mileage, typical city/highway split, and each car's official MPG and fuel type into the calculator separately. The output gives you a direct lbs CO₂ comparison on your specific driving pattern, which is more accurate than relying on manufacturer label figures alone. If you drive mostly city miles, a hybrid will look dramatically better than its highway MPG suggests. You can also project multi-year emissions by multiplying the annual figure by your intended ownership period. Combining emissions data with fuel cost calculations gives you both the environmental and financial case for choosing the lower-emission vehicle.