Using the converter
Type a figure and its unit: `30 mpg`, `12 km/L`, `35 mpg UK`. The answer shows km per litre first, then every other unit. Japan's official fuel economy figures are in km/L, and several other countries use it too, so this is the conversion for comparing a car rated that way with one rated in mpg.
How to convert mpg to km/L
Both units are distance over fuel, so they go up together and the conversion is a single multiplication. For US mpg, multiply by 0.425144: 30 mpg is 12.75 km/L. For UK mpg, multiply by 0.354006.
The factors are exact ratios. A mile is 1.609344 km, a US gallon 3.785411784 litres and a UK gallon 4.54609 litres, so 1 US mpg is 1.609344 ÷ 3.785411784 = 0.425144 km/L. Going back, divide by the same factor, or multiply km/L by 2.352 for US mpg.
Two gallons
The US and UK gallons parted ways in 1824, when Britain's Weights and Measures Act defined the imperial gallon as the volume of 10 pounds of water. The US kept the older wine gallon of 231 cubic inches. The imperial gallon is about 20% bigger, so a car's UK mpg rating is about 20% higher than its US one, and comparing them without converting flatters the British figure.
Questions
Why are UK mpg figures higher than US ones?
A UK (imperial) gallon is 4.54609 litres and a US gallon 3.785411784, about 20% smaller. The same car goes 20% further on a UK gallon.
What is 30 mpg in km/L?
12.75 km/L for US mpg, or 10.62 km/L for UK mpg.
What is 15 km/L in mpg?
About 35.3 US mpg, or 42.4 UK mpg.
Which countries use km/L?
Japan uses it for official fuel economy figures, and it's common in several other countries. Most of Europe uses L/100 km instead.
Sources
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