Free tools · no sign-up needed
MPG calculator
Find your car's real miles per gallon from one tank of gas. It also converts to liters per 100 km and works out what fuel costs you per mile.
Your fuel economy
26.4 miles per gallon
- Liters per 100 km
- 8.9
- Km per liter
- 11.2
- Fuel cost per mile
- $0.12
- Fuel cost per 100 mi
- $12.29
One tank tells you a little. Milebook works out MPG on every fill-up and warns you when it drops, which is often the first sign of a problem.
Track MPG automaticallyFree for 2 vehicles. No credit card.
How to measure MPG accurately
Fill the tank until the pump clicks off and reset your trip meter (or write down the odometer). Drive normally. At your next fill-up, fill to the click again and note the gallons. Miles driven divided by gallons added is your MPG.
Why your number differs from the sticker
Window-sticker MPG comes from lab tests. Short trips, cold weather, highway speed, idling, roof racks, underinflated tires and towing all lower real-world economy. Comparing tank to tank over time tells you more than any single reading.
The formula
MPG = miles driven ÷ gallons used. Liters per 100 km = 235.215 ÷ MPG. Fuel cost per mile = price per gallon ÷ MPG.
Questions
Do I need to fill the tank all the way?
For an accurate single reading, yes: fill to the click at both fill-ups. If you sometimes fill partway, add up all the gallons between two full fill-ups and divide the miles between them by that total.
What's a good MPG?
It depends on the vehicle. The useful comparison is against your own average: a tank that's 10% or more worse than usual is worth a look (tire pressure first).
How do I convert MPG to L/100 km?
Divide 235.215 by your MPG. 30 MPG is about 7.8 L/100 km.
Tired of typing in receipts? Milebook's Smart Receipt Scanner reads your gas and repair receipts from a photo and fills in the entry for you, free. See how it works