Fuel Economy Converter

What this tool does

This converter changes a car's fuel economy from one unit into another across the four figures drivers actually use: US miles per gallon, UK (Imperial) miles per gallon, kilometres per litre, and litres per 100 kilometres. Type a number, pick the unit you are converting from and the unit you want, and the result updates live as you type. Use the swap button to flip the two units in one click. It answers everyday questions like what 30 US MPG is in L/100km, why a UK MPG figure looks better than the US one for the same car, or how a European L/100km rating compares to km per litre.

How the conversion works

Litres per 100 km is the base unit because it is an inverse measure — a lower number means better economy, while MPG and km/L go the other way where higher is better. Every value is first turned into L/100km using exact factors (US MPG uses 235.214583 ÷ mpg, UK MPG uses 282.480936 ÷ mpg, and km/L uses 100 ÷ km/L), then converted out to your target unit with the reverse of that same math. Because US and UK gallons differ in size, the two MPG scales are not interchangeable, and this tool keeps them separate. Zero and negative inputs are rejected since they would mean infinite consumption, and the math is fully deterministic: the same input always gives the same result.