Fuel Economy Converter
Convert fuel economy between MPG, L/100km, and km/L.
30 MPG (US) also equals 12.75 km/L.
To convert US MPG to L/100km, divide 235.215 by the MPG — so 30 MPG = 235.215 ÷ 30 = 7.84 L/100km, which is 12.75 km/L. MPG and L/100km are inverse scales: higher MPG means a more efficient car, but lower L/100km does. km/L simply flips L/100km (100 ÷ L/100km).
Three ways to say the same thing
The United States rates cars in miles per gallon (MPG) — distance you travel per unit of fuel, so bigger is better. Most of the world quotes litres per 100 kilometres (L/100km) — fuel burned over a fixed distance, so smaller is better. Elsewhere you will see kilometres per litre (km/L), a distance-per-fuel figure like MPG where bigger is again better. This converter moves a value between all three at once.
235.215 uses the US gallon (3.785 L); for the UK imperial gallon (4.546 L) use 282.481 instead.
- 1 Note which unit you have. US MPG and km/L go up with efficiency; L/100km goes down. Getting this backwards is the most common mistake.
- 2 Convert MPG to L/100km. Divide 235.215 by the MPG figure. For a 30 MPG car: 235.215 ÷ 30 = 7.84 L/100km.
- 3 Convert MPG to km/L. Multiply MPG by 0.425144. For 30 MPG: 30 × 0.425144 = 12.75 km/L.
- 4 Convert L/100km to km/L. Divide 100 by the L/100km figure. For 8 L/100km: 100 ÷ 8 = 12.5 km/L, and 235.215 ÷ 8 = 29.4 MPG.
- 5 Check you used the right gallon. These figures assume the US gallon. A UK imperial gallon is about 20% larger, so an “imperial MPG” looks better than the same car’s US MPG.
MPG ↔ L/100km ↔ km/L
US gallon basis (235.215). Values rounded for display.
| MPG (US) | L/100km | km/L |
|---|---|---|
| 15 | 15.68 | 6.38 |
| 20 | 11.76 | 8.50 |
| 25 | 9.41 | 10.63 |
| 30 | 7.84 | 12.75 |
| 40 | 5.88 | 17.01 |
| 50 | 4.70 | 21.26 |
Why L/100km runs the opposite way to MPG
MPG and km/L measure distance per unit of fuel, so a bigger number means the car goes further on the same fuel — better economy. L/100km flips the ratio: it measures fuel per fixed distance, so a smaller number means less fuel burned — also better economy. Because they are reciprocals of each other (scaled by a constant), you divide rather than multiply to switch between them, which is why the conversion is 235.215 ÷ MPG and not a simple factor.
US vs imperial gallon. This tool uses the US gallon of 3.785 litres, giving the constant 235.215. The UK (imperial) gallon is larger at 4.546 litres, so its constant is 282.481 and an imperial MPG figure looks roughly 20% higher than the US MPG for the very same vehicle. Always check which gallon a spec sheet or advert means before comparing cars across regions.