CO2 Emissions per Mile/km Calculator

Carbon emissions from transportation are calculated by combining fuel consumption with emissions factors, meaning the mass of CO2 released per unit of fuel burned.

Core driving formula:

CO2 per mile = CO2 per gallon / Fuel Economy (MPG)

Total CO2 = Distance × CO2 per mile

CO2 emissions factors by fuel type:

Diesel produces more CO2 per gallon, but diesel engines typically achieve 20–30% better fuel economy, making the per-mile emissions comparable.

That last point is why the fuel selector also changes the fuel economy, not just the emissions factor. The MPG figures in the vehicle table below are gasoline figures. Pick diesel and the calculator raises them by 25%, pick E85 and it lowers them by 27%, because those are the real-world economy differences and ignoring them gives badly wrong answers.

E85 is the one that catches people out. Ethanol carries about a quarter less energy per gallon than gasoline, so an E85 vehicle burns proportionally more of it. Comparing the per-gallon emissions factors alone makes E85 look roughly 27% cleaner than gasoline. Per mile, once the economy penalty is applied, the two come out within a few percent of each other. The genuine climate argument for ethanol is about the carbon absorbed while the corn grows, which is a whole separate accounting question and not something a tailpipe figure can answer.

Average CO2 per mile by vehicle type (US):

Worked example: A commuter drives 12,000 miles per year in an SUV averaging 22 MPG. CO2 per mile = 8,887 / 22 = 403.95 g/mile, which the calculator rounds to 404 for display Annual CO2 = 12,000 × 403.95 = 4,847 kg (10,689 lbs) That is nearly 5 metric tons of CO2 per year, just from commuting. Multiply the rounded 404 instead and you get 4,848, which is the same answer to the precision this deserves.

Putting it in perspective:

• The average American generates ~16 metric tons of CO2 per year (all sources)
• Transportation accounts for ~27% of US greenhouse gas emissions
• Each gallon of gasoline not burned saves about 19.6 lbs of CO2
• Carpooling with one other person immediately halves your per-person emissions

Electric vehicle note: Electric vehicle emissions vary dramatically by electricity source, which is why the grid selector exists. The calculator assumes 3.5 miles per kWh, roughly what a Tesla Model 3 or a Chevy Bolt manages, and multiplies by the grid intensity you choose.

On the US average grid of 386 g CO2/kWh that works out to about 110 g/mile, comfortably better than any petrol car on the list. On a coal-heavy grid it is around 234 g/mile, still ahead of a sedan but behind a good hybrid. In the Pacific Northwest or Iceland it falls under 30 g/mile, at which point the manufacturing footprint of the battery dominates the lifetime total and the driving is close to free.

None of this counts the battery itself, which is typically quoted at 6 to 10 tonnes of CO2 for a mid-size pack. Divided over 150,000 miles that adds roughly 40 to 65 g/mile, and the EV still wins on any grid except the very dirtiest.