MPG to L/100km converter
Convert US miles per gallon to litres per 100 km, or back, with the formula and the constants it uses.
Nothing you enter leaves this page.
Fuel use in litres per 100 kmFuel economy in US miles per gallon
L/100kmUS mpg
Rounded to one decimal.
How this is calculated
US mpg counts miles per gallon, so a bigger number is better. L/100km counts litres per 100 kilometres, so a smaller number is better. Each is the other turned upside down, with a constant that converts gallons to litres and miles to kilometres.
L/100km = 235.215 ÷ mpg and mpg = 235.215 ÷ (L/100km)
The method, the constants and the limits are written out in how fuel cost is calculated.
Where 235.215 comes from
One US gallon is 3.785412 litres and one mile is 1.609344 kilometres, both from the NIST Guide to the SI, Appendix B (the mile is exact). For one mile you use 1 ÷ mpg gallons, which is 3.785412 ÷ mpg litres. That mile is 1.609344 km, so for 100 km you scale by 100 ÷ 1.609344.
L/100km = 100 × 3.785412 ÷ (1.609344 × mpg) = 235.215 ÷ mpg
This page converts US gallons only. Imperial (UK) gallons are a different size, so a figure quoted in imperial mpg will not give the right answer here.
Worked example: 30 US mpg
235.215 ÷ 30 = 7.84, which rounds to 7.8 L/100km. In reverse, 235.215 ÷ 7.8 = 30.2 mpg. The small difference is the rounding to one decimal place.
Conversion tables
Both tables are worked out from the formula above, rounded to one decimal.
| US mpg | L/100km |
|---|---|
| 10 | 23.5 |
| 15 | 15.7 |
| 20 | 11.8 |
| 25 | 9.4 |
| 30 | 7.8 |
| 35 | 6.7 |
| 40 | 5.9 |
| 45 | 5.2 |
| 50 | 4.7 |
| 55 | 4.3 |
| 60 | 3.9 |
| L/100km | US mpg |
|---|---|
| 4 | 58.8 |
| 5 | 47.0 |
| 6 | 39.2 |
| 7 | 33.6 |
| 8 | 29.4 |
| 9 | 26.1 |
| 10 | 23.5 |
| 12 | 19.6 |
| 15 | 15.7 |
| 20 | 11.8 |
Why a lower L/100km is better
L/100km measures how much fuel you burn over a fixed distance, so less is better. mpg measures how far you go on a fixed amount of fuel, so more is better. That also means the same change in mpg is worth different amounts. Going from 10 to 15 mpg saves far more fuel over a trip than going from 40 to 45 mpg, which a litres-per-distance figure shows more clearly.
To turn a fill-up into an mpg or L/100km figure, use the fuel consumption calculator. To put a cost on it, use the fuel cost calculator. More background is in how fuel cost is calculated. A single-value example is on the 20 mpg to L/100km page.
Common questions
Is this for US or UK gallons?
US gallons. A UK (imperial) gallon is a different size, so imperial mpg figures need a different constant, which this page does not offer.
Why does converting back not give exactly the same number?
The result is rounded to one decimal. Converting a rounded value back can move the last digit.
Why is L/100km used outside the US?
It states fuel use for a fixed distance, which makes the cost of a trip easy to work out. Many countries quote fuel economy this way.