Guide

Comparing consumption: l/100 km and mpg

Europe states consumption in litres per 100 kilometres, Anglo-American countries in miles per gallon. The two scales run in opposite directions — a lower figure is better on one and worse on the other.

Two scales, opposite directions

Litres per 100 kilometres states how much fuel a fixed distance needs. Miles per gallon states how far a fixed amount takes you. With l/100 km a smaller figure is more economical, with mpg a larger one. The two quantities are inverse to each other: 5 l/100 km equals about 47 mpg US.

Why there are two mpg values

The US gallon measures 3.785411784 litres, the imperial gallon 4.54609 litres. The same consumption therefore yields different figures: 5 l/100 km is about 47 mpg US but about 56.5 mpg imp. The difference is about 20 %. British vehicle tests use mpg imp, North American ones mpg US, and the abbreviation mpg alone does not say which is meant.

The conversion is not linear

Because the scales are inverse, the conversion is not a multiplication by a fixed factor. Between 4 and 5 l/100 km the difference is about 11.8 mpg US, while between 9 and 10 l/100 km it is only about 2.6 mpg US. When comparing improvements, compare the l/100 km figures rather than adding mpg differences.

Consumption figures are standardised values

Manufacturer figures come from standardised test procedures on a test bench. They serve to compare vehicles, not to predict actual everyday consumption. Driving style, route profile, load, tyre pressure and outside temperature all influence real consumption considerably. Unit arithmetic does not change that; it only converts between scales.

Matching conversions

Matching tables

Unit family: Fuel economy

Sources