How to use the fuel economy converter (us, uk, metric)
- Enter the fuel economy value you have.
- Choose its unit: US mpg, imperial mpg, liters per 100 km, kilometers per liter or miles per liter.
- Optionally open the advanced options and enter a trip distance in kilometers to see the fuel used.
- Read the value in every unit, and use the reference table to compare common figures.
Formula
km per liter = miles per gallon x 1.609344 / liters per gallon
US gallon = 3.785411784 L, imperial gallon = 4.54609 L, mile = 1.609344 km
liters per 100 km = 100 / km per liter
Every value is first turned into kilometers per liter, and that is then converted to the other units. Because liters per 100 km measures fuel used per distance, a bigger number means worse economy, which is the opposite of mpg.
A car that gets 30 US mpg
At 30 US miles per gallon, kilometers per liter is 30 x 1.609344 / 3.785411784 = 12.7543, so liters per 100 km is 100 / 12.7543 = 7.840. In imperial gallons the same car gets 30 x 4.54609 / 3.785411784 = 36.03 miles per gallon.
A car rated 6.5 liters per 100 km is 36.19 US mpg. A car rated 45 imperial mpg uses 6.277 liters per 100 km. For a 500 km trip at 7.84 liters per 100 km the car burns 39.2 liters.
Why UK and US mpg differ
The mile is the same in both places, but the gallon is not. An imperial gallon is 4.54609 liters and a US gallon is 3.785411784 liters, so the imperial gallon is about 20 percent bigger. The same car therefore shows a figure about 1.2 times higher in imperial mpg than in US mpg.
When you compare ratings from different countries, check which gallon is meant. Metric ratings in liters per 100 km avoid the problem.
Reading the reference table
The table converts common US mpg values to the other units. It shows that going from 15 to 20 mpg saves more fuel than going from 40 to 50 mpg on the same distance: 15 mpg is 15.68 L/100 km and 20 mpg is 11.76, a difference of about 3.9 liters per 100 km, while 40 mpg is 5.88 and 50 mpg is 4.70, a difference of about 1.2.
That is why liters per 100 km is often a fairer way to compare the fuel saved by a more efficient car. To work out your own mpg from fill-ups, use the MPG Calculator.
Assumptions and limits
- The mile is exactly 1.609344 kilometers.
- The US gallon is exactly 3.785411784 liters and the imperial gallon is exactly 4.54609 liters.
- Fuel economy is treated as a steady average. Driving conditions are not modeled.
- Electric vehicle ratings such as MPGe are not converted.
- Values must be above zero.
Frequently asked questions
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure to get liters per 100 km. For example 235.215 / 30 is 7.84. For imperial mpg, divide 282.481 by the figure.
Is a higher L/100 km better?
No. It is the amount of fuel used for 100 km, so a lower number means a more efficient car. mpg works the other way around, with higher being better.
Why does the same car have two mpg numbers?
Because US and imperial gallons differ in size. A car that gets 30 miles from a US gallon gets more miles from the larger imperial gallon.
Can I convert km per liter to mpg?
Yes. Choose kilometers per liter as the unit, and the page shows US and imperial mpg together with liters per 100 km.