MPG Calculator
Work out your car's miles per gallon from the miles driven and litres used.
Fuel economy
45.5MPG
- Litres per 100 km
- 6.21 L/100km
Based on UK gallons (4.546 litres).
v1.0 · Reviewed September 2026
How this is worked out
Litres are converted to UK gallons at 4.54609 litres each, then miles are divided by gallons. The metric line converts to litres per 100 km.
Worked example
- 300 miles
- 30 litres
30 ÷ 4.54609 = 6.6 gallons, and 300 ÷ 6.6
45.5 MPG, which is 6.21 L/100km
Assumptions and limits
- Uses UK gallons, so the result is not comparable with US MPG figures, which are about 17% lower for the same car.
- Accurate only if you brim the tank at the start and end of the measured distance, since a part fill makes the litres figure unreliable.
- Litres per 100 km moves the opposite way to MPG: a lower number is better.