Enter a fuel economy figure in any one unit and get the same consumption expressed in MPG (US), MPG (Imperial), litres per 100 km and kilometres per litre.
Fuel economy is stated two different ways around the world: distance per unit of fuel (MPG, km/L), where higher is better, and fuel per unit of distance (litres per 100 km), where lower is better. The conversion runs through litres per 100 km: MPG (US) equals 235.215 divided by the L/100 km figure. The US and Imperial figures differ because the gallons differ: a US gallon is 3.785 litres while an Imperial gallon is 4.546 litres, so the same car shows a higher MPG number in Imperial gallons even though its actual consumption is unchanged. Published test-cycle figures and real-world consumption also differ, so converted figures keep the accuracy of the number entered.
Why are US and Imperial MPG different? Because the gallons are different sizes. A US gallon is 3.785 litres and an Imperial gallon is 4.546 litres, so one Imperial gallon takes a car further and the Imperial MPG figure is higher for exactly the same fuel consumption.
How is L/100 km converted to MPG? For US MPG, divide 235.215 by the litres per 100 km figure. For Imperial MPG, divide 282.481 by it. The reverse conversions use the same constants divided by the MPG figure.
Is a higher L/100 km figure better or worse? Worse. Litres per 100 km measures fuel used, so lower is more economical. With MPG and km/L the opposite applies: higher means the vehicle goes further on the same fuel.