How to Estimate Your Car's Carbon Footprint

Every liter or gallon of fuel a car burns releases a predictable amount of carbon dioxide. That makes your car's CO2 emissions surprisingly easy to estimate.

CO2 per unit of fuel

The US Environmental Protection Agency estimates:

• Gasoline: about 8.89 kg of CO2 per gallon (roughly 2.35 kg per liter)
• Diesel: about 10.18 kg per gallon (roughly 2.69 kg per liter)

These figures cover the CO2 from burning the fuel itself, not the emissions from producing and transporting it.

The formula

A gasoline car averaging 30 MPG and driven 12,000 miles a year uses 400 gallons: 400 × 8.89 ≈ 3,556 kg, about 3.6 tonnes of CO2 a year.

In metric: 15,000 km at 7 L/100 km uses 1,050 liters, and 1,050 × 2.35 ≈ 2,470 kg.

Electric cars

An electric car has no tailpipe emissions, but the electricity it uses may come partly from fossil fuels:

A car using 18 kWh per 100 km for 15,000 km uses 2,700 kWh. On a grid emitting 0.4 kg of CO2 per kWh, that's about 1,080 kg, and less on a cleaner grid. Grid emissions vary widely by country, region and time of day.

Ways to cut emissions

• Drive smoothly and keep tires properly inflated.
• Remove roof racks and extra weight when you don't need them.
• Combine errands into one trip, share rides, or swap short drives for walking or cycling.

Putting it in context

Comparing your car's number with other parts of your footprint, such as home heating, electricity and flights, shows where changes make the biggest difference.