What is a Fuel Economy Converter?
The fuel economy converter switches between km/L, L/100km, and mpg.
How it's calculated
L/100km = 100 ÷ (km/L)
1 US mpg = 0.425 km/L, 1 UK mpg = 0.354 km/L
Units that are easy to mix up
| Units | Why it's confusing | How to tell them apart |
|---|---|---|
| km/L vs L/100km | Opposite directions | Higher is better for km/L, lower is better for L/100km — easy to mix up |
| US mpg vs UK mpg | Different gallon sizes | The same car reads 30 mpg in the US but 36 mpg in the UK |
km/L and L/100km move in opposite directions
km/L is better when higher; L/100km is better when lower — an inverted relationship that trips people up. Improving from 10 to 12 km/L and from 20 to 22 km/L both look like '+2' on that scale, but the actual fuel saved is 3.7x greater for the first case. That's exactly why L/100km, used across much of Europe, directly reflects real savings.
Good to know
- Improving a poor-mileage vehicle saves more fuel than improving an already-efficient one. This counterintuitive effect is sometimes called the 'MPG illusion.'
- US and UK mpg are not the same — because the gallon itself differs. The same car can read 30 mpg in the US and 36 mpg in the UK.
- Official ratings are typically a combined cycle — a weighted average of city and highway driving — so your real mileage depends on how closely your driving matches that mix.
- Electric vehicles use km/kWh or MPGe, where MPGe treats 33.7 kWh as energy-equivalent to one gallon of gasoline.
- Hybrid vehicles often get better mileage in city driving due to regenerative braking, the opposite pattern from gas-only cars.
Frequently asked questions
Q. What is 12 km/L in L/100km?
About 8.3 L/100km. Calculate as 100 ÷ 12.
Q. Which country's mpg standard is being used?
Check the source — the US gallon (3.785 L) and UK gallon (4.546 L) are different sizes.
Q. What is combined fuel economy?
A weighted average of city and highway driving cycles, used as the official rating.