How it works
To measure your real fuel economy, fill the tank and reset the trip odometer. Next time you fill up, enter the miles on the trip meter and the gallons it took to refill.
Averaging over several tanks gives a steadier number, because pumps shut off at slightly different levels each time.
The result is also shown as liters per 100 km, the measure used in most countries, and as gallons per 100 miles, which makes it easier to compare how much fuel two cars actually use.
Formula
MPG = miles ÷ gallons; L/100 km = 235.215 ÷ MPG
Questions people ask
Why is my MPG lower than the EPA rating?
EPA ratings come from standardized lab tests. Short trips, cold weather, highway speeds over 65 mph, heavy loads and idling all reduce real-world mileage.
Is this US or imperial gallons?
US gallons (3.785 L). An imperial gallon is 4.546 L, so UK mpg figures are about 20% higher for the same car.
Why look at gallons per 100 miles?
Fuel used is not linear in MPG. Going from 10 to 20 mpg saves 5 gallons per 100 miles, while going from 30 to 40 saves under 1. Gallons per 100 miles shows the real difference.