Units of fuel per fixed distance Generally expressed as liters per 100 kilometers (L/100 km), used in Europe, China, South Africa, Australia and New Zealand.
Canadian law allows for use of either liters per 100 kilometres or miles per Imperial gallon.[2][3] Recently, the window sticker on new US cars has started displaying the vehicle's fuel consumption in US gallons per 100 miles.[4] Units of distance per fixed fuel unit Miles per gallon (mpg) is commonly used in the United States and the United Kingdom, or kilometres per litre (km/L) is more commonly used elsewhere in the Americas, Eurasia, parts of Africa and Oceania. When the mpg unit is used, it is necessary to identify the type of gallon used, as the Imperial gallon is 4.5 liters and the US gallon is 3.785 liters.
Conversions of units:
miles per US gallon → L/100 km: 235 / mpgUS = L/100 km
miles per Imp. gallon → L/100 km: 282 / mpgImp. = L/100 km
L/100 km → miles per US gallon: 235 / (L/100 km) = mpgUS
L/100 km → miles per Imp. gallon: 282 / (L/100 km) = mpgImp.
http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles#Units_of_measure