Units explained
US MPG vs UK MPG
A US gallon and an imperial gallon contain different volumes. An MPG figure without a gallon definition is incomplete.
Use the right gallon
One US liquid gallon is 3.785411784 litres. One imperial gallon is 4.54609 litres. A mile is 1.609344 km in both systems. Since the imperial gallon contains more fuel, UK MPG is numerically higher for the same underlying consumption.
Convert a familiar figure
30 US MPG is approximately 12.75 km/L, 7.84 L/100km or 36.03 UK MPG. A vehicle advertised at 36 UK MPG is therefore close to 30 US MPG, not 20% more efficient. The fuel-economy converter uses the full unit factors before rounding results.
Do not confuse units with test procedures
Unit conversion puts figures on the same scale; it does not make different test cycles equivalent. Compare figures measured under the same protocol where possible. Real-world temperature, driving style and traffic also affect consumption.
Method and references
Examples use nominal geometry and fixed-price scenarios, with no vehicle-specific specifications implied. See our calculation methodology and editorial policy.
Unit reference: NIST Guide to the SI: conversion factors. Financial examples are arithmetic illustrations, not market-price forecasts.