Updated October 2026
The formula
km/L and MPG point the same way: both are distance per unit of fuel, so higher is better and the conversion is a plain multiplication. No reciprocals, no flipping.
km/L = US MPG × 0.4251
US MPG = km/L × 2.352
For UK MPG: km/L = UK MPG × 0.354.
The 0.4251 is 1.609 km per mile divided by 3.785 litres per US gallon. Worked example: a compact sedan rated at 36 US MPG combined.
- 36 × 0.4251 = 15.3 km/L
- As L/100 km: 100 ÷ 15.3 = 6.53 L/100 km
- Over a 400 km week: 400 ÷ 15.3 = 26.1 litres
The converter does the same chain without rounding in between, and the link it copies includes the figure, so you can send someone the exact result.
km/L tables
MPG to km/L for the common US figures:
| US MPG | km/L | L/100 km |
|---|---|---|
| 15 | 6.38 | 15.68 |
| 20 | 8.50 | 11.76 |
| 25 | 10.63 | 9.41 |
| 30 | 12.75 | 7.84 |
| 35 | 14.88 | 6.72 |
| 40 | 17.01 | 5.88 |
| 50 | 21.26 | 4.70 |
And km/L to MPG, for figures from Japanese, Indian and Latin American spec sheets:
| km/L | US MPG | UK MPG | L/100 km |
|---|---|---|---|
| 8 | 18.8 | 22.6 | 12.50 |
| 10 | 23.5 | 28.2 | 10.00 |
| 12 | 28.2 | 33.9 | 8.33 |
| 15 | 35.3 | 42.4 | 6.67 |
| 18 | 42.3 | 50.8 | 5.56 |
| 20 | 47.0 | 56.5 | 5.00 |
| 25 | 58.8 | 70.6 | 4.00 |
| 30 | 70.6 | 84.7 | 3.33 |
Catalogue km/L vs the km/L you get
Converting the unit is the easy part. The harder part is that the figure you started from was measured in a lab, on a test cycle, and every market uses a different one: EPA in the US, WLTP in Europe, WLTC in Japan, the ARAI test in India. A 25 km/L catalogue claim and a 20 km/L owner report can both be honest. They measure different driving.
Rough gaps between the label and the road, by type of driving:
| Driving | Typical result vs label | Why |
|---|---|---|
| Steady highway at moderate speed | Close to label, sometimes above | Few stops, engine at its best load |
| Mixed suburban | 5 to 15% below | Lights, short trips, air conditioning |
| Dense city traffic | 15 to 30% below | Idling and stop-start burn fuel at 0 km/L |
| Short cold trips | 20 to 40% below | Engine never reaches temperature |
Hybrids turn the city row upside down, because they recover energy when braking. Everything else follows it. If you want the figure for your own car and your own commute, the only method that works is filling up twice and dividing, which the gas mileage calculator does in kilometres and litres as well.
km/L or L/100 km?
Both are metric, both are correct, and they are each other's reciprocal times 100. km/L is easier to picture: one litre, this far. L/100 km is easier to budget with, because fuel cost scales with it in a straight line: 8 L/100 km at 1.50 a litre is 12 per 100 km, and 6 L/100 km is 9. If you are comparing two cars, L/100 km also shows the real saving more fairly. The MPG to L/100km converter covers that side, with the reasoning.