Abbreviation for "miles per gallon," as a measure of fuel consumption. The U.S. gallon is 3.785 liters. The Imperial gallon is 20% larger (4.546 liters). When a vehicle gets 30 mpg (US), he will get 36 mpg (Imperial). The metric system calculates fuel consumption as the number of liters per 100 kilometers. The same vehicle will be giving 7.8 l/100 km.