Fuel Economy Converter

Convert between UK MPG, US MPG, L/100 km, and km/L

All conversions use kilometres per litre (km/L) as a canonical intermediate value, which avoids rounding errors when chaining between units. Litres per 100 kilometres is a volume-per-distance unit, so it converts through a reciprocal: km/L = 100 ÷ (L/100 km). Results maintain full floating-point precision internally and are formatted for readability.

Units supported

• Miles per gallon, UK (mpg) — distance per Imperial gallon (4.54609 litres). Used in the UK and Ireland.
• Miles per gallon, US (mpg) — distance per US liquid gallon (3.785411784 litres). A US gallon is about 17% smaller than an Imperial gallon, so the two mpg figures are never interchangeable.
• Litres per 100 km (L/100 km) — fuel used per distance, standard across Europe and most of the world. Lower is better.
• Kilometres per litre (km/L) — distance per litre, common in Asia and South America. Higher is better.

Reference values

• 40 mpg (UK) = 33.31 mpg (US) = 7.06 L/100 km = 14.16 km/L
• L/100 km = 282.481 ÷ mpg (UK) and L/100 km = 235.215 ÷ mpg (US)
• A typical small petrol car: 5–6 L/100 km
• A typical SUV: 8–10 L/100 km