km/L is MPG in metric
Kilometres per litre is what MPG would be if the US had gone metric. Both count distance per unit of fuel, so both get bigger as the car gets more efficient. That makes this the most intuitive conversion on the site: multiply by a factor and you are done, with none of the reciprocal awkwardness that L/100km brings.
The catch is that the factor is small. A litre is a little over a quart, and a kilometre is about five eighths of a mile, so one mile per gallon is only 0.425144 km per litre. Numbers that look impressive in MPG look modest in km/L. A 50 mpg hybrid is a 21 km/L hybrid. Readers moving between the two systems often assume a km/L figure is a poor one when it is simply a smaller unit.
The formula
km/L = MPG (US) × 0.425144
The factor is 1.609344 divided by 3.785411784: the kilometres in a mile over the litres in a US gallon. For imperial gallons the factor is 1.609344 over 4.54609, which is 0.354006. Toggle the gallon type on the converter to switch between them.
Both factors are computed at full precision from the exact definitions; the six-decimal values above are for readers who want to check the arithmetic by hand.
A worked example
A Japanese-market compact is advertised at 14.9 km/L on the WLTC cycle. What is that in MPG? Divide by 0.425144 and you get 35.0 mpg (US). Working the other way, a 35 mpg American sedan multiplied by 0.425144 is 14.88 km/L. The two cars are near enough identical in efficiency, allowing for the different test cycles.
For a British reader the same 35 mpg, now imperial, is 35 times 0.354006, or 12.39 km/L. This is not a smaller number because the car is worse; it is smaller because an imperial mpg is a bigger unit.
Where km/L is the standard
Japan's catalogue figures are published in km/L, first on the JC08 cycle and since 2018 on WLTC. India's ARAI certification uses km/L (usually written kmpl), and it is the figure every Indian car advertisement leads with. Brazil, Indonesia, Thailand, Pakistan and the Gulf states also use it in everyday speech and in most marketing, even where L/100km appears on official paperwork.
If you drive in one of those markets and read reviews from the US or UK, this converter and its reverse are the two you will use most. Litres and liters are the same unit throughout; only the spelling differs by country. So does the abbreviation: km/L, kmpl, km/lt and kmL all appear on spec sheets and all mean kilometres per litre.
Mistakes to watch for
- Applying the US factor to a UK figure. Imperial mpg times 0.425144 overstates km/L by 20%.
- Confusing km/L with L/100km. They are reciprocals of each other: km/L is 100 divided by L/100km. A car at 5 L/100km does 20 km/L.
- Comparing a JC08 or ARAI figure directly with an EPA one. The Indian and older Japanese cycles are gentler than the EPA's and produce higher numbers for the same car.
- Writing kmpl and km/L as if they were different units. They are the same thing.