Litres/litres per 100 kilometres - Fuel is sold in litres these days because the European Union demands it. There are 4.5461 litres in a gallon. European car makers calculate fuel consumption on the basis of how many litres a car needs to cover 100 kilometres (62 miles) at a certain speed. To convert this figure to mpg, divide 282.5 by the litres per 100km figure.