⛽ Fuel Economy Converter
Convert fuel consumption between US miles per gallon, imperial mpg, liters per 100 km and kilometers per liter.
Quick answer: L/100 km = 235.21 ÷ US mpg. So 30 mpg (US) is 7.84 L/100 km, which is also 36.03 mpg (UK) and 12.75 km/L.
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Fuel Economy Converter inputs
Result
30 mpg (US)
7.84 L/100 km
| mpg (US) | 30 |
| mpg (UK / imperial) | 36.03 |
| L/100 km | 7.84 |
| km/L | 12.75 |
Fuel for 100 miles: 3.33 US gal · Fuel for 100 km: 7.84 L
mpg to L/100 km chart
| mpg (US) | L/100 km | mpg (UK) | km/L |
|---|---|---|---|
| 10 | 23.52 | 12.01 | 4.25 |
| 15 | 15.68 | 18.01 | 6.38 |
| 20 | 11.76 | 24.02 | 8.5 |
| 25 | 9.41 | 30.02 | 10.63 |
| 30 | 7.84 | 36.03 | 12.75 |
| 35 | 6.72 | 42.03 | 14.88 |
| 40 | 5.88 | 48.04 | 17.01 |
| 45 | 5.23 | 54.04 | 19.13 |
| 50 | 4.7 | 60.05 | 21.26 |
| 60 | 3.92 | 72.06 | 25.51 |
How to convert fuel economy
All four units are linked through kilometres per litre. US mpg uses the 3.785 L US gallon, UK mpg uses the 4.546 L imperial gallon, and one mile is 1.609 km. Because L/100 km is "fuel per distance", it is the inverse of the others.
km/L = mpg(US) × 1.609344 ÷ 3.785412 · L/100 km = 100 ÷ km/L = 235.215 ÷ mpg(US) = 282.481 ÷ mpg(UK)
Worked example
30 mpg (US): 30 × 1.609344 ÷ 3.785412 = 12.75 km/L. Then 100 ÷ 12.75 = 7.84 L/100 km. In imperial gallons, 30 × 4.54609 ÷ 3.785412 = 36.03 mpg (UK).
Quick reference
| L/100 km | mpg (US) | mpg (UK) |
|---|---|---|
| 4 | 58.8 | 70.6 |
| 5 | 47.0 | 56.5 |
| 6 | 39.2 | 47.1 |
| 8 | 29.4 | 35.3 |
| 10 | 23.5 | 28.2 |
| 12 | 19.6 | 23.5 |
Why the units run in opposite directions
Americans and Britons describe how far a car goes on a fixed amount of fuel, so bigger numbers are better. Most of the rest of the world describes how much fuel is needed to cover a fixed distance, so smaller numbers are better. Because one is the reciprocal of the other, equal steps in mpg do not mean equal fuel savings: improving from 15 to 20 mpg (US) saves about 3.9 L every 100 km, while improving from 40 to 45 mpg saves only 0.65 L. That is why many economists prefer fuel-per-distance figures when comparing cars and estimating running costs.
Tips
- Compare savings in L/100 km: going from 10 to 20 mpg saves far more fuel than going from 40 to 50 mpg, which mpg figures hide.
- Check which gallon a review uses – UK and US mpg differ by about 20%.
- Real-world economy is often 10–20% worse than official test figures.
Frequently asked questions
Why is the conversion not a simple multiplication?
Miles per gallon measures distance per fuel, while L/100 km measures fuel per distance – one is the reciprocal of the other. So L/100 km = 235.21 ÷ mpg (US), and doubling mpg halves L/100 km.
What is the difference between US and UK mpg?
An imperial (UK) gallon is 4.546 L and a US gallon is 3.785 L, so the same car shows about 20% more mpg in UK figures. Multiply US mpg by 1.201 to get UK mpg.
Is a higher or lower L/100 km better?
Lower is better: it is the litres of fuel needed to drive 100 km. For mpg and km/L, higher is better.
What is good fuel economy?
For a modern petrol car, under 6 L/100 km (about 40 mpg US) is very efficient, 6–8 L/100 km is typical, and over 10 L/100 km (under 24 mpg US) is thirsty.