Why does UK vs US gallon matter?

A UK (imperial) gallon is 4.546 litres while a US gallon is 3.785 litres. The same MPG figure therefore represents better real fuel economy in UK gallons than in US gallons, so picking the right type is essential.

Why are MPG and L/100km inverse?

MPG measures distance per unit of fuel (higher is better), while L/100km measures fuel per fixed distance (lower is better). One is the reciprocal of the other, scaled by unit conversions.

Is any data sent to a server?

No — the conversion runs entirely in your browser and nothing is uploaded.

MPG to L/100km Converter

Convert miles-per-gallon to litres-per-100km and back, UK or US gallons.

MPG ⇄ L/100km converter

Convert between miles per gallon and litres per 100 km in either direction. Choose UK (imperial) or US gallons — they differ in size, so the same MPG number maps to a different L/100km figure.

The conversion is exact (1 mile = 1.609344 km; 1 UK gallon = 4.54609 L; 1 US gallon = 3.785412 L) and runs entirely in your browser, so nothing is uploaded.