MPG Calculator

Calculate your car's real-world MPG from a fill-up, or convert between MPG, L/100km and km/L fuel economy figures.

Calculation type

Miles driven since last fill-up

Litres of fuel used (fill-up amount)

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Enter your fill-up data to calculate real-world MPG.

MPG Conversion Formulas

MPG to L/100km: divide 282.5 by MPG. L/100km to MPG: divide 282.5 by L/100km. MPG to km/L: multiply by 0.4251. These conversions use the Imperial gallon (4.546L) as used in UK fuel economy figures — not the US gallon (3.785L). Always use Imperial MPG when comparing UK cars.

Official WLTP figures are measured under controlled lab conditions — constant temperature, no AC, optimal tyre pressure, no cargo weight. Real-world driving involves cold starts, stop-start traffic, motorway speeds above the test cycle, climate control use, and vehicle load. A typical real-world MPG is 10–20% below WLTP. Short journeys (under 5 miles) dramatically reduce average MPG because the engine never reaches optimal operating temperature.