Fuel Economy Converter (km/L, L/100km, mpg)

Converts fuel economy between kilometres per litre, litres per 100 km, US miles per gallon and UK miles per gallon. Kilometres per litre and litres per 100 km are reciprocals, so a higher value in one means a lower value in the other.

Explanation

Enter a fuel economy figure and choose its unit, and every other unit follows. Kilometres per litre convert to mpg exactly as easily as litres per 100 km convert back.

Three conventions

Countries measure fuel economy in incompatible ways.

Japan — km/L, the distance covered on a litre. Higher is better
Europe — L/100km, the fuel needed for 100 km. Lower is better
United States — mpg, miles per gallon. Higher is better

The conversions

Kilometres per litre and litres per 100 km are reciprocals.

\text{L/100km} = \dfrac{100}{\text{km/L}}

The mpg figure follows from 1 mile = 1.609344 km and 1 US gallon = 3.785411784 L.

\text{mpg (US)} = \text{km/L} \times \dfrac{3.785411784}{1.609344} = \text{km/L} \times 2.352

Example

Convert 15 km/L.

\dfrac{100}{15} = 6.667\ \text{L/100km} \qquad 15 \times 2.352 = 35.28\ \text{mpg (US)}

Watch out

US and UK mpg are different numbers. The imperial gallon (4.54609 L) is about 20% bigger than the US gallon (3.785411784 L), so the same car scores higher in the UK. Our 15 km/L is 35.28 mpg in America but 42.37 mpg in Britain.

Because km/L and L/100km run in opposite directions, averaging them needs care. A car doing 20 km/L and one doing 10 km/L over the same distance average 13.33 km/L — the harmonic mean — and not 15.