Fuel Economy Converter
Enter a fuel economy value and choose your source and target units to convert instantly between US MPG, UK (Imperial) MPG, liters per 100km, and kilometers per liter.
How the Fuel Economy Converter formula works
Unlike most conversions, MPG and L/100km have an inverse relationship, since one measures distance-per-fuel and the other measures fuel-per-distance:
L/100km = 235.215 / MPG (US) MPG (US) = 235.215 / L/100km km/L = 100 / L/100km MPG (UK) = MPG (US) × 1.20095
Step-by-step calculation
- Convert the entered value to L/100km first, since it's the common reference point this calculator uses internally.
- From L/100km, convert to the target unit using its specific relationship — inverting for MPG-based units, or a straightforward ratio for km/L.
Worked example
Converting 30 MPG (US) to L/100km: 235.215 / 30 ≈ 7.84 L/100km — meaning that car uses about 7.84 liters of fuel to travel 100 kilometers.
Frequently asked questions
Why is a UK gallon different from a US gallon?
A UK (Imperial) gallon is about 20% larger than a US gallon, so the same physical car gets a higher 'MPG' number when measured in Imperial gallons than in US gallons, even though the actual fuel efficiency is identical.
Why does a lower L/100km number mean better efficiency, while a lower MPG means worse?
L/100km measures fuel consumed per fixed distance, so less fuel used is better (lower is better). MPG measures distance traveled per unit of fuel, so covering more distance is better (higher is better) — they're inverse framings of the same underlying efficiency.