MPG to L/100 km
Convert miles per gallon to litres per 100 km. Divide 235.21 by the mpg figure — the conversion is a division, not a multiplication.
Runs in your browser
The formula
L/100km = 235.2146 ÷ mpg (US)
L/100km = 282.4809 ÷ mpg (imperial)Divide, do not multiply. The units measure opposite things — mpg is distance per fuel, L/100 km is fuel per distance — so a bigger mpg gives a smaller L/100 km. No single factor can express that.
Where the constants come from:
100 × 3.785411784 ÷ 1.609344 = 235.2146 (US gallon)
100 × 4.54609 ÷ 1.609344 = 282.4809 (imperial gallon)Each constant is its own inverse. Dividing 235.2146 by an L/100 km figure gives the mpg back. See L/100km to mpg.
Which gallon
| mpg | L/100km if US | L/100km if imperial |
|---|---|---|
| 20 mpg | 11.76 | 14.12 |
| 25 mpg | 9.41 | 11.30 |
| 30 mpg | 7.84 | 9.42 |
| 35 mpg | 6.72 | 8.07 |
| 40 mpg | 5.88 | 7.06 |
| 50 mpg | 4.70 | 5.65 |
| 60 mpg | 3.92 | 4.71 |
A figure from a British source read as a US one is 20% out. British magazines quote imperial mpg; American ones quote US mpg; neither says which.
Quick reference, US gallons
| mpg (US) | L/100km | km/L |
|---|---|---|
| 15 mpg | 15.68 | 6.4 |
| 20 mpg | 11.76 | 8.5 |
| 25 mpg | 9.41 | 10.6 |
| 30 mpg | 7.84 | 12.8 |
| 35 mpg | 6.72 | 14.9 |
| 40 mpg | 5.88 | 17.0 |
| 45 mpg | 5.23 | 19.1 |
| 50 mpg | 4.70 | 21.3 |
| 60 mpg | 3.92 | 25.5 |
The improvements that matter are at the bottom
Because the relationship is reciprocal, ten extra mpg is worth far more at 15 mpg than at 50. Over 10,000 km:
| Change | Fuel saved |
|---|---|
| 15 → 25 mpg | 627 L |
| 25 → 35 mpg | 269 L |
| 35 → 45 mpg | 149 L |
| 45 → 55 mpg | 95 L |
The first row saves nearly seven times what the last one does, and every row is the same ten-mpg step. If a household has two cars, improving the thirsty one is worth several times improving the efficient one.
Working it out without a calculator
Divide 235 by the mpg, rounding as you go — the answers are forgiving because a tenth of a litre per 100 km is well inside the noise of real driving:
| mpg | 235 ÷ mpg | Rounded |
|---|---|---|
| 24 | 9.8 | ~10 L/100km |
| 30 | 7.8 | ~8 L/100km |
| 47 | 5.0 | ~5 L/100km |
24 mpg is about 10 L/100 km and 47 mpg is about 5 are the two anchors that make everything else interpolable.