Gas Mileage Calculator
Calculate your vehicle's fuel economy in MPG from miles driven and gallons used.
Try an example
28 mpg
About this calculator
How This Gas Mileage Calculator Works
Enter miles driven and gallons of gas used, and the calculator returns your fuel economy in miles per gallon, plus the metric equivalent.
Worked Example
Driving 350 miles on 12.5 gallons of gas works out to 28 mpg — equivalent to about 8.4 liters per 100 km.
The Formula
MPG = Miles driven ÷ Gallons used. For the metric equivalent, liters per 100 km isn't a simple unit conversion of MPG — it's an inverted measure (higher MPG means lower L/100km), calculated as 235.215 ÷ MPG.
Getting an Accurate Measurement
The most reliable way to measure real-world MPG: fill the tank completely, reset the trip odometer, drive normally, then fill up again and record both the miles driven and the gallons needed to refill — that refill amount reflects what was actually used, more accurately than reading a dashboard estimate. Since mileage varies by driving conditions, averaging several fill-ups gives a more representative number than any single tank.
Worked example
Driving 350 miles on 12.5 gallons of gas works out to 28 mpg — equivalent to about 8.4 liters per 100 km.
Frequently asked questions
How do I measure gallons used accurately?
Fill the tank completely, reset your trip odometer, drive normally, then fill up again and note both the miles driven and the gallons needed to refill — that refill amount is what was actually used.
Why does my mileage vary between fill-ups?
City driving, highway driving, weather, tire pressure, and load all affect fuel economy — tracking mileage over several fill-ups gives a more reliable average than any single tank.