US and Imperial gallons are different. Higher MPG means better efficiency, while lower L/100km means better efficiency; zero cannot be converted with a reciprocal formula.
How to use this fuel economy converter
- Enter a number in either value field.
- Choose the starting and target units.
- Copy the calculated result or swap the direction.
Convert MPG and litres per 100 kilometres
Fuel economy is reported differently across vehicle markets. The US and some imported specifications use miles per US gallon, the UK commonly uses miles per Imperial gallon, and Ireland and mainland Europe use litres per 100 kilometres. This converter includes all three standards plus kilometres per litre, with each gallon size labelled explicitly.
US MPG and Imperial MPG are not the same
One US gallon is exactly 3.785411784 litres. One Imperial gallon is exactly 4.54609 litres. Because the Imperial gallon is larger, the same vehicle receives a higher Imperial MPG number: 30 US MPG is approximately 36.0285 Imperial MPG. Never compare two MPG figures until you know which gallon definition each source uses.
MPG to L/100km formulas
For US MPG, use L/100km = 235.214583 ÷ MPG. For UK or Imperial MPG, use L/100km = 282.480936 ÷ MPG. The reciprocal formula works in both directions. For example, 30 US MPG is approximately 7.84049 L/100km, while 30 Imperial MPG is approximately 9.41603 L/100km.
Why better efficiency points in opposite directions
MPG measures distance from a fixed amount of fuel, so a higher number is better. L/100km measures fuel used over a fixed distance, so a lower number is better. The relationship is reciprocal rather than linear: doubling MPG halves L/100km, and zero cannot be converted because division by zero has no finite result.
Kilometres per litre
Kilometres per litre also measures distance per fuel amount, so higher is better. Convert it with L/100km = 100 ÷ km/L. A vehicle achieving 20 km/L uses 5 L/100km. Use this unit for specifications from markets that report metric distance per litre rather than consumption per 100 kilometres.
Compare vehicle specifications safely
Published fuel economy can come from different laboratory test cycles and real driving varies with speed, weather, load, tyres and route. This tool converts the stated unit accurately; it does not make test cycles equivalent or predict fuel cost. Use the dedicated MPG to litres per 100km converter for US MPG, or the Imperial MPG converter for UK specifications.
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