Fuel Economy Converter — MPG, L/100km, km/L & More

Because mpg and L/100km are inversely related — they measure opposite things. MPG is distance per volume (how far you go on a gallon), while L/100km is volume per distance (how much fuel you burn to go 100 km). Doubling your mpg does NOT halve your L/100km. For example: 10 mpg = 23.5 L/100km, 20 mpg = 11.8 L/100km (L/100km halved), but 40 mpg = 5.9 L/100km, 80 mpg = 2.9 L/100km. Each doubling of mpg cuts L/100km in half, but the absolute savings decrease at higher efficiencies.

A US gallon is 3.785 liters, while a UK (imperial) gallon is 4.546 liters — about 20% larger. This means the same car will show a higher number in UK mpg than US mpg. For example, a car doing 30 US mpg would get about 36 UK mpg. Always check which gallon your source uses. Canadian vehicles are sometimes advertised with US mpg on window stickers alongside L/100km, adding to the confusion. This converter handles both systems precisely.

For gasoline cars in 2025: Excellent: under 6 L/100km (over 39 US mpg) — hybrids and efficient compacts. Good: 6-8 L/100km (29-39 US mpg) — modern sedans and hatchbacks. Average: 8-10 L/100km (24-29 US mpg) — typical SUVs and crossovers. Poor: 10-13 L/100km (18-24 US mpg) — large SUVs and trucks. Very Poor: over 13 L/100km (under 18 US mpg). Electric vehicles are measured in MPGe (miles per gallon equivalent) — most EVs achieve 100-140 MPGe, but the direct comparison is tricky because electricity costs differ from gasoline.

Fill your tank completely and reset the trip odometer. Drive normally until the tank is nearly empty. Fill the tank again completely and note the gallons pumped (or liters). Divide the miles driven by gallons used: mpg = miles ÷ gallons. For L/100km: (liters pumped ÷ km driven) × 100. For best accuracy, repeat this across 3-5 fill-ups and average the results. The EPA estimates on window stickers are usually slightly optimistic — real-world mileage is typically 5-15% lower depending on driving conditions, traffic, and climate.

Fuel economy drops significantly above 50 mph (80 km/h) due to aerodynamic drag, which increases with the square of speed. At 55 mph, most cars achieve peak efficiency. At 75 mph, fuel economy is typically 15-25% worse than at 55 mph. For a car getting 30 mpg at 55 mph, expect about 23 mpg at 75 mph — a $350+ annual difference for a typical commuter. Other factors: aggressive acceleration can reduce economy by 10-30%, carrying roof cargo reduces it by 5-25%, and cold weather reduces it by 10-20% due to thicker oil and longer warm-up times.