The difference lies in the gallon size. A US gallon equals 3.785 liters, while a UK (Imperial) gallon equals 4.546 liters—about 20% larger. This means UK MPG figures appear roughly 20% higher than US MPG for the same vehicle. For example, 30 MPG (US) is equivalent to about 36 MPG (UK). Always check which gallon standard is being used when comparing fuel economy figures between American and British sources.

To convert from US MPG to L/100km, divide 235.215 by the MPG value. For example: 235.215 ÷ 30 MPG = 7.84 L/100km. For UK MPG to L/100km, divide 282.481 by the MPG value. For example: 282.481 ÷ 40 MPG (UK) = 7.06 L/100km. You can use our converter above to instantly calculate these conversions.

European countries use the metric system, measuring fuel consumption as liters per 100 kilometers (L/100km) rather than miles per gallon. This metric directly tells you how many liters of fuel are consumed to travel 100 km—lower numbers indicate better efficiency. It's essentially the inverse of the MPG concept. L/100km makes it easier to calculate fuel costs for a trip: simply multiply by the distance (in hundreds of km) and the fuel price per liter.

Excellent: 40+ MPG (US) / 48+ MPG (UK) / below 5.9 L/100km / 17+ km/L — typical for hybrids and efficient diesels.
Good: 30–40 MPG (US) / 36–48 MPG (UK) / 5.9–7.8 L/100km / 12.7–17 km/L — common for compact and midsize cars.
Fair: 20–30 MPG (US) / 24–36 MPG (UK) / 7.8–11.8 L/100km / 8.5–12.7 km/L — typical for larger sedans and small SUVs.
Poor: Below 20 MPG (US) / 24 MPG (UK) / above 11.8 L/100km / below 8.5 km/L — large trucks, performance vehicles.

Fuel efficiency directly impacts CO₂ emissions. Each liter of gasoline burned produces approximately 2.3 kg of CO₂, while diesel produces about 2.7 kg per liter. A car that consumes 8 L/100km emits roughly 184 g CO₂ per km (gasoline). Improving fuel economy from 20 MPG to 30 MPG (US) reduces emissions by about 33%. This is why governments worldwide set increasingly strict fuel economy and emissions standards.

Kilometers per liter (km/L) is a fuel efficiency metric commonly used in Japan, India, Brazil, and several other countries. It measures how many kilometers a vehicle can travel on one liter of fuel—higher numbers mean better efficiency. To convert: 15 km/L ≈ 35.3 MPG (US) ≈ 42.4 MPG (UK) ≈ 6.67 L/100km. The km/L unit is intuitive for metric-system countries that prefer "distance per volume" rather than "volume per distance."