Fuel Efficiency Calculator
Calculate your vehicle's fuel economy from distance driven and fuel used, in L/100 km, km/L and US or UK mpg.
About the Fuel Efficiency Calculator
Fill the tank, reset the trip meter, drive, then refill and note the fuel added: that's the fuel used for the distance. L/100 km (lower is better) is used in Europe, Canada and Australia; mpg (higher is better) in the US and UK, but a UK gallon is 4.546 L and a US gallon 3.785 L, so UK mpg figures are 20% higher.
The formula
L/100 km = litres ÷ km × 100; mpg = miles ÷ gallons
Worked example
Example: Fuel economy = 29.2 mpg
- Inputs: Units: miles, US gal; Distance driven: 380; Fuel used: 13; Fuel price per litre or gallon: $4.
- Formula: L/100 km = litres ÷ km × 100; mpg = miles ÷ gallons
- Result: Fuel economy = 29.2 mpg
Questions people ask
Why is my mpg lower than advertised?
Official tests (EPA, WLTP) use set cycles; speed, cold, short trips and load reduce real economy.
How do I convert mpg to L/100 km?
235.21 ÷ US mpg, or 282.48 ÷ UK mpg.