Two opposite ways to report efficiency

US mpg and km/L report distance traveled per unit of fuel, so a higher number means better economy. L/100 km reports fuel consumed for a fixed distance, so a lower number means better economy.

The conversion relationship

One US gallon equals exactly 3.785411784 liters and one international mile equals exactly 1.609344 kilometers. To convert US mpg to km/L, multiply by 1.609344 and divide by 3.785411784. Convert km/L to L/100 km by dividing 100 by km/L.

US and imperial gallons differ

This tool uses the US liquid gallon. Imperial mpg uses a larger gallon and produces a different number for the same vehicle. Confirm which gallon a specification uses before comparing ratings.

Check a 30 mpg conversion

Thirty US mpg multiplied by 1.609344 and divided by 3.785411784 equals about 12.7543 km/L. Dividing 100 by that value gives about 7.8405 L/100 km. Converting 7.8405 L/100 km back should return about 30 US mpg. Because L/100 km is the reciprocal form, averaging two displayed L/100 km or mpg values directly can be misleading when the trips cover different distances.

Compare vehicles on the same basis

Use figures from the same test procedure, fuel, model configuration, and unit convention. For your own records, divide actual distance by actual fuel added over several complete fill cycles; do not rely on one partial refill or dashboard estimate. Hybrid and electric operation, idling, towing, temperature, terrain, and charging losses can require different measures. This converter preserves only the fuel-economy relationship and does not translate mpg into operating cost or emissions.

Published ratings and real fuel use can differ because of speed, traffic, weather, terrain, load, maintenance, driving style, and test procedure. Results are unit conversions, not consumption predictions.