Fuel Economy Converter
Convert between MPG (US and UK), L/100km, km/L, and miles per liter.
Why this isn't a simple multiplication
MPG and km/L measure how far you travel per unit of fuel — a bigger number means better efficiency. L/100km measures the opposite: how much fuel you use per fixed distance — a smaller number means better efficiency. Converting between the two families requires a division (100 ÷ value), not a multiplication, which is why L/100km can't share a simple conversion factor with the others.
Common conversions
- 30 MPG (US) ≈ 7.84 L/100km ≈ 12.75 km/L
- A US gallon (3.785 L) is smaller than a UK/Imperial gallon (4.546 L), so the same car gets a higher MPG(US) number than MPG(UK) for identical real-world fuel use
- 40 MPG (UK) ≈ 7.07 L/100km
- Lower L/100km = more efficient; higher MPG or km/L = more efficient
Frequently asked questions
Why do US and UK gallons give different MPG numbers for the same car?
A US gallon (3.785 liters) is about 17% smaller than a UK/Imperial gallon (4.546 liters). Since MPG is miles per gallon, the same car burning the same amount of fuel per mile will show a higher MPG(US) number than MPG(UK), purely because the US gallon is a smaller unit of volume.
Which unit should I use to compare cars?
L/100km is often considered the most intuitive for comparing absolute fuel costs, since it directly represents fuel used per fixed distance — the difference between a 5 and a 6 L/100km car is a consistent real amount of fuel, whereas the same absolute MPG difference means very different things at low vs. high MPG values.