Enter a value in any fuel economy unit and instantly see the equivalent in mpg (US), mpg (UK), km/L and L/100km.
| Unit | Value |
|---|
Fuel economy is reported two fundamentally different ways around the world: as "distance per volume" (miles per gallon in the US and UK, kilometers per liter elsewhere) or as "volume per distance" (liters per 100 km in most of Europe and beyond). These aren't just different units — they're inverses of each other, which is why a bigger mpg number means better economy, but a bigger L/100km number means worse economy. This tool lets you enter a value once and see it converted to every common fuel economy unit at the same time.
Values must be positive — a fuel economy of zero or less isn't physically meaningful (it would imply infinite or undefined fuel use).
Miles per US gallon, miles per UK gallon and km/L are all "distance per volume" and scale directly against each other, using kilometers per liter (km/L) as the bridge unit:
L/100km measures "volume per distance" — the reciprocal relationship — so converting to or from it is a division, not a multiplication by a fixed factor:
This is why L/100km can't just be added to the same factor table as the other three units — it needs its own reciprocal step.
| Unit | Symbol | Relationship to km/L |
|---|---|---|
| Miles per US Gallon | mpg (US) | × 0.425143707 |
| Miles per UK Gallon | mpg (UK) | × 0.354006190 |
| Kilometers per Liter | km/L | × 1 (base unit) |
| Liters per 100 Kilometers | L/100km | = 100 ÷ km/L (reciprocal) |
Note: mpg (US) and mpg (UK) differ because the US gallon (3.785411784 L) and UK gallon (4.54609 L) are different sizes — the same mpg number means better real-world economy in the UK gallon than the US gallon.
Example 1 — L/100km to mpg (US)
A car rated at 8 L/100km: km/L = 100 ÷ 8 = 12.5 km/L, ÷ 0.425143707 ≈ 29.4 mpg (US).
Example 2 — mpg (US) to L/100km
A car rated at 30 mpg (US): 30 × 0.425143707 ≈ 12.75 km/L, then 100 ÷ 12.75 ≈ 7.84 L/100km.
Example 3 — mpg (US) vs mpg (UK)
A car advertised as "40 mpg" without specifying which gallon: in US gallons that's 40 × 0.425143707 ≈ 17.0 km/L; in UK gallons, 40 × 0.354006190 ≈ 14.2 km/L — a meaningful difference, which is why the unit needs to be specified.
Example 4 — Why Lower L/100km Is Better
Car A: 5 L/100km (20 km/L). Car B: 10 L/100km (10 km/L). Car A uses half the fuel to go the same distance — for L/100km, lower is always more efficient, the opposite of mpg.