Gas Mileage Calculator
Calculate your car's real fuel economy in mpg and L/100 km from distance driven and fuel used.
How to measure your real mpg
- Fill the tank completely and reset the trip meter.
- Drive normally until the tank is at least half empty.
- Fill up again and note how many gallons it took.
- Divide the miles driven by the gallons added.
350 miles on 11.2 gallons is 31.3 mpg, or 7.5 L/100 km. At $3.45 a gallon, fuel costs about 11 cents a mile.
Why your mpg differs from the sticker
EPA ratings come from standardized lab tests. Real-world economy is often 10–20% lower due to highway speeds above 65 mph, cold weather, short trips, air conditioning, roof racks and heavy loads. Average several fill-ups for a reliable figure, and use the fuel cost calculator to plan trips with it.
Frequently asked questions
How do I calculate gas mileage?
Divide the miles driven by the gallons used to refill the tank.
Is the dashboard mpg accurate?
Trip computers are usually within a few percent but often read slightly optimistic. The fill-up method is the most reliable.
What reduces gas mileage most?
High speeds, aggressive acceleration, under-inflated tires, extra weight and short trips in cold weather.
Last reviewed October 2026. Results are estimates; check important decisions with a qualified professional.