Vehicle GHG Emissions Calculator
Transportation is the largest source of greenhouse gas emissions in the US, accounting for about 29 percent of total US GHG emissions (EPA 2023). Personal vehicles (cars, trucks, SUVs) account for the majority of transportation emissions. This calculator estimates CO2 emissions from gasoline consumption using the EPA emission factor of 8.887 kg CO2 per gallon of gasoline burned. You can enter either your annual fuel consumption directly or your miles driven and vehicle fuel economy, and the calculator will compute annual CO2 emissions in kilograms and metric tons.
Vehicle emissions formula (EPA)
Gallons/yr = Miles/yr / MPG
CO2 (kg/yr) = Gallons/yr * Emission factor (kg CO2/gal)
CO2 (metric tons/yr) = CO2 (kg/yr) / 1000
CO2/mile (g/mile) = CO2 (kg/yr) / Miles/yr * 1000
The emission factor of 8.887 kg CO2/gallon for gasoline is from EPA's GHG Emission Factors Hub (2024). It represents tailpipe CO2 only. The carbon content of gasoline is approximately 2,421 g C per gallon, which combusts to produce 8,887 g (8.887 kg) of CO2 per gallon (EPA).
Reducing vehicle emissions
- Improving fuel economy by 10 MPG (e.g., from 20 to 30 MPG) reduces annual emissions by about 33 percent.
- Switching from a 25 MPG car to a plug-in hybrid (50 MPGe) cuts emissions roughly in half, even before considering electric miles.
- Remote work eliminating one 30-mile daily commute saves about 1.5 to 2 metric tons of CO2 per year.
- Proper tire inflation (recommended PSI) can improve fuel economy by 0.5 to 3 percent (DOE).
- Transportation accounts for 29 percent of US GHG emissions (EPA 2023 inventory), more than any other sector.
Frequently asked questions
What is the EPA emission factor for gasoline?
The EPA emission factor for gasoline is 8.887 kg of CO2 per gallon burned (EPA GHG Emission Factors Hub, 2024). This is for tailpipe CO2 only and does not include upstream (extraction, refining, transport) emissions, which add roughly 20 to 25 percent more on a lifecycle basis.
What are the emission factors for other fuels?
Per EPA's 2024 GHG Emission Factors: diesel: 10.180 kg CO2/gallon; ethanol (E85): ~5.75 kg CO2/gallon (blended); compressed natural gas: 5.444 kg CO2/GGE. Diesel has higher CO2 per gallon but much better fuel economy, so per-mile emissions can be similar to or lower than gasoline.
How do I calculate annual vehicle emissions?
Annual emissions = annual miles driven / MPG * 8.887 kg CO2/gallon. For example, driving 12,000 miles per year at 30 MPG = 400 gallons * 8.887 = 3,554.8 kg = 3.55 metric tons of CO2 per year.
What is the average US car CO2 emission per mile?
Based on the EPA average new light-duty vehicle fuel economy of about 28 MPG and the gasoline factor of 8.887 kg/gallon, the average is about 8.887/28 = 0.317 kg CO2/mile, or approximately 317 g/mile. The EPA uses 0.404 kg CO2/mile for the average fleet including older vehicles.
Do electric vehicles have zero tailpipe emissions?
Electric vehicles produce zero direct tailpipe CO2 emissions. However, generating the electricity to charge them does produce emissions (unless using 100% renewables). The EPA's Power Profiler tool estimates per-kWh emissions for your regional grid. The emissions per mile of an EV are typically 50 to 70 percent lower than a gasoline vehicle, even on the average US grid.
Official sources
- EPA: GHG Emission Factors Hub (2024).
- EPA: EPA Green Vehicle Guide.
- DOE: fueleconomy.gov (EPA MPG ratings).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.