MPG to L/100km Converter
A reciprocal conversion, not a ratio, with both gallons handled separately. Two ways to get this wrong, and most converters only fix one.
Enter a number above zero.
You can't multiply your way to this answer. More miles per gallon is better; fewer liters per 100 km is better. They are reciprocals, so you divide rather than multiply. Anyone who applies a conversion factor here gets a number that looks plausible and is wrong.
The formulas
L/100 km = 282.481 ÷ imperial mpg
US mpg = 235.215 ÷ L/100 km
The constants come from combining the mile, the gallon and the liter. For the US case: one mile is 1.609344 km and one US gallon is 3.785411784 liters, and 100 × 3.785411784 ÷ 1.609344 gives 235.215.
Two errors, not one
The reciprocal is the first trap. The gallon is the second: an imperial gallon is about 17 percent larger than a US one, so the same car reads about 20 percent better in UK mpg. A car advertised at 50 mpg in Britain is doing about 42 US mpg, and neither number is dishonest.
Get both wrong at once and the error compounds. The systems guide covers why the two gallons differ.
Conversion table
| US mpg | L/100 km | Imperial mpg | km/L |
|---|---|---|---|
| 10 | 23.52 | 12.0 | 4.25 |
| 15 | 15.68 | 18.0 | 6.38 |
| 20 | 11.76 | 24.0 | 8.50 |
| 25 | 9.41 | 30.0 | 10.63 |
| 30 | 7.84 | 36.0 | 12.75 |
| 35 | 6.72 | 42.0 | 14.88 |
| 40 | 5.88 | 48.0 | 17.01 |
| 45 | 5.23 | 54.0 | 19.13 |
| 50 | 4.70 | 60.0 | 21.26 |
| 60 | 3.92 | 72.1 | 25.51 |
| 70 | 3.36 | 84.1 | 29.76 |
| 80 | 2.94 | 96.1 | 34.01 |
Why L/100km is arguably the better measure
Fuel per distance scales linearly with what you spend, so the difference between 10 and 9 L/100km is the same saving as between 6 and 5. Distance per fuel doesn't: going from 20 to 25 mpg saves far more fuel than going from 45 to 50, even though both are a five unit gain.
That non-linearity is why mpg comparisons between very different vehicles can mislead, and it is a direct consequence of the reciprocal relationship above.
Common questions
How do I convert mpg to L/100km?
Divide 235.215 by the US mpg figure. It is a division, not a multiplication, because the two are reciprocals: mpg measures distance per fuel, and L/100km measures fuel per distance.
Why can't I just multiply by a conversion factor?
Because higher mpg is better and lower L/100km is better. They run in opposite directions, so no single multiplier works. Multiplying is the most common error in this conversion.
Is UK mpg the same as US mpg?
No. The imperial gallon is about 17 percent larger, so a UK figure is roughly 20 percent higher than the US figure for the same car. A UK 50 mpg is about 42 US mpg.
What is 30 mpg in L/100km?
30 US mpg is 7.84 L/100 km. 30 imperial mpg is 9.42 L/100 km.
Related converters and guides
Sources
- NIST Guide to the SI, Appendix B: Conversion Factors. National Institute of Standards and Technology. Source for every conversion factor on this page, and for which factors are exact rather than rounded.