MPG to L/100km: How to Compare Fuel Economy Between the US and Europe
Why Fuel Economy Units Confuse Car Shoppers: The US and Canada advertise fuel economy in miles per gallon (mpg), the UK also uses mpg but with a different-sized gallon, and continental Europe uses litres per 100 kilometres (L/100km). Comparing a car review from a European site to a North American one requires more than a simple lookup table.
The Key Insight: MPG and L/100km Are Inversely Related. Higher mpg means better fuel economy, but higher L/100km means worse fuel economy — they move in opposite directions, so you cannot average or scale them linearly. The correct formulas are: L/100km = 235.215 ÷ mpg(US), and L/100km = 282.481 ÷ mpg(UK). The constants differ because the US gallon (3.785 litres) and the Imperial/UK gallon (4.546 litres) are different sizes.
Quick Reference Table (US mpg to L/100km): 20 mpg = 11.76 L/100km. 30 mpg = 7.84 L/100km. 40 mpg = 5.88 L/100km. 50 mpg = 4.70 L/100km. 60 mpg (hybrid territory) = 3.92 L/100km.
Real-World Comparisons: A European compact car rated at 5.5 L/100km converts to roughly 42.8 mpg (US) — competitive with a North American compact. A hybrid rated at 4.0 L/100km converts to about 58.8 mpg (US), which explains why European hybrid ratings often look unremarkable at first glance until you convert them.
The US vs UK mpg Trap: A UK or European car spec sheet quoting "60 mpg" almost certainly means Imperial gallons, which converts to roughly 50 mpg (US) — a meaningfully lower number. Shoppers who compare a UK-spec "60 mpg" hatchback to a US-spec "50 mpg" model without converting units may wrongly assume the UK car is far more efficient when the real difference is much smaller.
The Most Common Fuel-Economy Math Mistake: Averaging mpg values directly across a trip or a fleet. Because mpg and L/100km are reciprocals of fuel consumption, the correct way to average fuel economy across multiple legs of a trip is to average the consumption (L/100km or gallons used), not the mpg figures themselves. Averaging mpg directly overstates the true combined efficiency.
Practical Tip: An OBD2 scanner reads your vehicle's real-time and trip-average fuel consumption directly from the onboard computer, often in whichever unit your dashboard defaults to. Convert that reading with ConvertNow to compare it honestly against a manufacturer's claimed rating from a different country.
Conclusion: Whether you are cross-shopping an imported vehicle, planning fuel costs for a European road trip, or just trying to make sense of a spec sheet, converting mpg and L/100km correctly — through the shared L/100km intermediate — avoids the reciprocal-math trap. Bookmark ConvertNow's fuel economy converter before your next car purchase.