Gas mileage calculator
Your car’s real fuel economy from odometer readings at each fill-up.
About this calculator
This gas mileage calculator works out your car's real fuel economy from your fill-ups. Enter the odometer reading and the fuel added each time you fill the tank.
It shows the average, the best and worst tanks, the economy in mpg and L/100 km, and what fuel costs you per mile or kilometre.
How it works
Fill the tank to full and note the odometer. At each later fill-up, the distance since the last one ÷ the fuel added gives the economy for that tank. The average divides the total distance by the total fuel.
Last reviewed:
Worked example
- Units: Miles and gallons
- One fill-up per line: odometer reading, then fuel added: 42150 0; 42468 11.2; 42790 11.6; 43105 10.9
- Fuel price per gallon: $3.50
Average fuel economy: 28.3 mpg (8.3 L/100 km)
Common questions
How do I calculate my gas mileage?
Fill the tank and note the odometer. At the next fill-up, divide the miles driven by the gallons added: 320 miles on 10 gallons is 32 mpg.
How do I convert mpg to L/100 km?
Divide 235.21 by the mpg figure. 30 mpg (US) is about 7.84 L/100 km.
Why is my real mileage lower than the official figure?
Short trips, high speeds, cold weather, under-inflated tyres and air conditioning all use more fuel than standard tests.
Sources and further reading
The story behind it
Where the idea came from: The US Environmental Protection Agency has rated the fuel economy of new cars since the 1970s, and since 2008 its tests include faster driving, air conditioning and cold weather.
Real mileage still varies with traffic, speed, tyres and load. Tracking your own fill-ups is the most accurate way to know what your car uses.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
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