Driving CO2 Emissions Calculator

How it works

Almost all the carbon in a fuel leaves the tailpipe as CO2, so tailpipe CO2 is the fuel burned times a fixed amount of CO2 per gallon. The fuel burned is the distance divided by the fuel economy.

EPA puts the CO2 from a gallon of gasoline at 8,887 grams and from a gallon of diesel at 10,180 grams. For E85, the factor is blended by volume from EPA's per-gallon factors for pure ethanol (5,750 g) and motor gasoline (8,780 g) at the ethanol share you enter. Ethanol carries less carbon per gallon, but an E85 vehicle also gets fewer miles per gallon, so enter the MPG it achieves on E85.

A fuel consumption figure in L/100 km is converted to miles per US gallon, and kilometres to miles, with exact unit definitions. Annual CO2 is shown in kilograms, metric tons (1,000 kg) and US short tons (2,000 lb).

Formula

gallons        = miles ÷ MPG
MPG from L/100 km = (100 ÷ L/100 km) × 3.785411784 ÷ 1.609344
CO2 (g)        = gallons × factor
factor         = 8,887 g/gal gasoline; 10,180 g/gal diesel
factor (E85)   = e × 5,750 + (1 − e) × 8,780 g/gal,   e = ethanol share
CO2 per mile   = factor ÷ MPG

Example

A 300-mile trip in a gasoline car that gets 25 mpg burns 300 ÷ 25 = 12 gallons and emits 12 × 8,887 g = 106.6 kg of CO2.

Driving 11,500 miles a year in the same car burns 460 gallons: 460 × 8,887 g = 4,088 kg, or 4.09 metric tons (4.51 short tons) of CO2, about 355 g per mile.

Assumptions and limitations

• Tailpipe CO2 only. Emissions from producing and delivering the fuel, other greenhouse gases (methane, nitrous oxide, refrigerant leaks) and the vehicle's manufacture are not included.
• Per-gallon factors are EPA's: gasoline and diesel from EPA-420-F-23-014 (June 2023); E85 blended from ethanol and motor gasoline in EPA's Emission Factors for Greenhouse Gas Inventories (15 January 2025), Table 2. EPA notes most U.S. gasoline is E10 and that its tailpipe CO2 per mile is similar to gasoline's.
• The E85 figure counts the CO2 from burning ethanol at the tailpipe. Greenhouse gas inventories often report that biogenic CO2 separately; it is included here because it leaves the tailpipe.
• Fuel economy is held constant; real mileage, and so real CO2, varies with speed, load, weather and traffic. Results are estimates, not a measured or certified emissions figure.

Frequently asked questions