Fuel Consumption Converter
Convert between miles per gallon, kilometres per litre and litres per 100 km. Some fuel-economy units are inversely related.
Written by Rahman · Last reviewed
Quick answer
Fuel economy is measured two opposite ways. Miles per gallon and kilometres per litre are distance per unit of fuel, where higher is better; litres per 100 km is fuel per unit of distance, where lower is better. Because they are reciprocals the conversion is not linear: going from 20 to 25 mpg saves twice as much fuel over the same distance as going from 40 to 50 mpg.
About the Fuel Consumption Converter
Fuel economy describes how far a vehicle travels per unit of fuel. It can be stated as distance per volume (miles per gallon or kilometres per litre) or as volume per distance, such as litres per 100 kilometres.
These two families are inversely related, so this converter handles the reciprocal maths automatically when switching between them.
Why mpg improvements are worth less at the top end
Miles per gallon is fuel economy expressed as distance per unit of fuel, which makes it an inverted scale. Equal-sized gains in mpg do not represent equal savings, and the effect is large enough to change which upgrade is worth making.
- Over 10,000 miles, going from 15 to 20 mpg saves about 167 gallons.
- From 20 to 25 mpg saves about 100 gallons.
- From 30 to 35 mpg saves about 48 gallons.
- From 40 to 45 mpg saves about 28 gallons.
Every step is a 5 mpg improvement, yet the first saves six times as much fuel as the last. Litres per 100 km avoids the trap entirely because it is already fuel per distance, so equal changes represent equal savings, which is one reason most of the world reports economy that way.
Frequently Asked Questions
Is a higher mpg better than a lower L/100km?
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Yes. Higher miles per gallon means better economy, while lower litres per 100 km means better economy. They describe the same thing from opposite directions.
Why is US mpg different from UK mpg?
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The US and imperial gallons differ in size, so the same car has a higher mpg figure in imperial (UK) gallons than in US gallons.
How do I convert mpg to L/100km?
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Divide 235.21 by the US mpg figure to get litres per 100 km. The conversion is not linear because the units are inversely related.