Fuel Economy Converter

Worked example

8 L/100 km = 12.5 km/L exactly, ≈ 29.40182292 mpg (US) and ≈ 35.31011704 mpg (Imperial). 30 mpg (US) is ≈ 7.840486111 L/100 km, but 30 mpg (Imperial) is ≈ 9.416031211 L/100 km, because an Imperial gallon is larger.

How it works

Fuel economy is not converted with a single multiplying factor. Litres per 100 km measures the fuel used, while km/L and miles per gallon measure the distance covered, so converting between the two flips the value: km/L = 100 ÷ (L/100 km). Converting km/L to miles per gallon is a plain multiplication. The two mpg units are always labelled because a US gallon (3.785411784 L) and an Imperial gallon (4.54609 L) differ, so 1 Imperial mpg is about 1.2009 US mpg. A lower L/100 km means a more efficient vehicle, while a higher km/L or mpg means a more efficient vehicle.

Zero has a special meaning. 0 L/100 km means no fuel is used, so km/L and mpg are not defined, and 0 km/L or 0 mpg means no distance is covered, so L/100 km is not defined. Those conversions show a message instead of a number, never an infinity. Converting 0 to the same unit, or between km/L and mpg, gives 0. Enter zero or more: a fuel-economy value cannot be negative. This converts a value you already have and is not a trip-cost or mileage calculator.

A result written as a plain number is exact. A result starting with “≈” has been rounded to 10 significant figures, because its exact decimal never ends or is too long to read comfortably. When an exact value is long, its full digits are shown underneath. The calculation itself is never rounded: only the display is.