How fuel economy conversion works
km/L and mpg both measure distance per unit of fuel, so they scale by a fixed factor. L/100km measures fuel per fixed distance instead, so it's the inverse of km/L — smaller numbers mean better economy.
- km/L — kilometers traveled per liter of fuel
- L/100km — liters used per 100 km — lower is better
- mpg(US) — miles per US gallon (3.785411784 L)
- mpg(UK) — miles per UK/imperial gallon (4.54609 L)
Common values
| Value (kmL) | Result |
|---|---|
| 1 kmL | 2.35215 mpg(US) |
| 2.5 kmL | 5.88036 mpg(US) |
| 5 kmL | 11.7607 mpg(US) |
| 10 kmL | 23.5215 mpg(US) |
| 15 kmL | 35.2822 mpg(US) |
| 20 kmL | 47.0429 mpg(US) |
| 30 kmL | 70.5644 mpg(US) |
| 50 kmL | 117.607 mpg(US) |
| 100 kmL | 235.215 mpg(US) |
More detail
Why L/100km is an inverse relationship
km/L and mpg both grow as fuel economy improves, but L/100km shrinks — it's fuel used per fixed distance, not distance per fuel. Because converting takes 100 divided by the value rather than a simple multiplication, an equal-sized step means different things in the two units. In L/100km, 4 → 3 and 12 → 11 each save exactly 1 L per 100 km. In km/L, 15 → 16 saves 0.417 L per 100 km while 30 → 31 saves only 0.107 L — nearly a fourfold gap, so the better the economy already is, the less fuel one extra km/L buys you.
Why US and UK gallons give different mpg
The US gallon (3.785411784 L) and the UK/imperial gallon (4.54609 L) are different volumes by definition, so the same car's fuel economy reads as a bigger number in mpg(UK) than mpg(US) — about 20% higher. Neither factor is a constant you have to take on trust: 3.785411784 ÷ 1.609344 = 2.352146 (US) and 4.54609 ÷ 1.609344 = 2.824809 (UK), and dividing those two gives 2.824809 ÷ 2.352146 = 1.2009 — the 'about 20%' itself.
Practical tip. Korean spec sheets list km/L, US spec sheets list mpg(US), and European spec sheets list L/100km — always check which unit a source uses before comparing numbers across countries.
Frequently asked questions
How many mpg is 10 km/L?
10 km/L × 2.352146 = 23.5215 mpg(US). Enter 10 above with From set to km/L and To set to mpg(US) to see this computed directly.
How do I convert L/100km to km/L?
L/100km and km/L are inverses of each other: divide 100 by the L/100km value. For example, a car rated 8 L/100km gets 100 ÷ 8 = 12.5 km/L.
Why is mpg(UK) different from mpg(US) for the same car?
The US gallon (3.785411784 L) is smaller than the UK/imperial gallon (4.54609 L), so the same fuel economy converts to a mpg(UK) figure about 20% higher than mpg(US) — the calculator uses factors 2.352146 and 2.824809 respectively.
Is a lower or higher L/100km number better?
Lower is better. Unlike km/L or mpg, L/100km measures how much fuel it takes to cover a fixed 100 km, so a smaller number means less fuel burned over that distance.