🚗 Gas Mileage Calculator
The honest way to measure fuel economy: fill the tank, reset the trip meter, drive, refill, and divide miles by gallons. No dashboard estimate needed.
Results also show L/100km and km per liter so the figure makes sense anywhere in the world.
How to use this calculator
Enter the miles you drove since the last fill-up and the gallons it took to refill, and get your true MPG plus metric equivalents.
- Fill the tank fully and reset your trip meter, or note the odometer.
- Drive normally, then refill the tank fully.
- Enter the Miles driven and the Gallons used.
- Read your MPG, plus liters per 100 km and km per liter.
Frequently asked questions
What formula does the Gas Mileage Calculator use?
Miles per gallon equals miles driven divided by gallons used. The metric figures derive from the exact conversion: liters per 100 km equals 235.214583 divided by MPG.
Can you give a worked example?
Driving 300 miles on 10 gallons gives 30 MPG, which equals 7.84 liters per 100 km or 12.75 km per liter.
Why measure this way instead of trusting the dashboard?
Dashboard estimates can be optimistic. The fill-to-fill method measures actual fuel burned over real miles, which is the honest number.
Does it use US or imperial gallons?
US gallons. If you work in imperial gallons, convert first: one imperial gallon is about 1.201 US gallons.