How to work out your MPG
- Choose your Units: US or UK gallons with miles, or litres with kilometres.
- Fill the tank and note the odometer or reset the trip meter. Drive as normal, then fill up again.
- Enter the distance (or both odometer readings) and the fuel the second fill-up took. Add the price to see the cost per mile or km.
The formulas
| Measure | Formula | 300 miles on 10 US gallons |
|---|---|---|
| US mpg | miles ÷ US gallons | 30 mpg |
| UK mpg | miles ÷ UK gallons | 36.03 mpg |
| L/100 km | litres ÷ km × 100 | 7.84 L/100 km |
| km/L | km ÷ litres | 12.75 km/L |
A mile is 1.609344 km, a US gallon 3.785411784 litres and a UK gallon 4.54609 litres.
Using your mpg
Once you know your real mpg, the fuel cost calculator prices any trip with it. Logging mpg at every fill-up is also a simple health check for the car: a sudden drop can mean low tyre pressure, a dragging brake or a sensor fault. To convert an mpg figure you already have, use the fuel economy converter.