Fuel Converter

About the Fuel Converter

Fuel economy is the one conversion where multiplying by a factor gives the wrong answer, because the two families run in opposite directions. Miles per gallon and kilometres per litre measure distance covered per unit of fuel, so bigger is better. Litres per 100 kilometres measures fuel burned over a fixed distance, so smaller is better. Going between them means dividing rather than multiplying, and this tool detects that and prints the reciprocal formula it used.

The headline relationship is that 235.214583 divided by a US mpg figure gives litres per 100 kilometres. A 30 mpg car therefore uses 7.84 L/100km, and a 40 mpg car uses 5.88. Notice the saving from 20 to 25 mpg is larger than the saving from 40 to 45, which is the practical reason many countries switched to the litres per distance form in the first place.

Gallons are the other trap. The imperial gallon is 4.54609 litres against 3.785411784 for the US gallon, so a British magazine quoting 45 mpg describes a thirstier car than an American one quoting the same number. Both are listed separately, along with kilometres per gallon and gallons per 100 miles, which the United States now prints on window stickers. Zero cannot be converted across the reciprocal boundary, so the tool reports that rather than returning infinity.

How to use

1. Enter the economy figures, one per line.
2. Pick the unit your source uses, such as mile per US gallon.
3. Pick the unit you want, such as litre per 100 km.
4. Check the reciprocal formula line, then copy the values.