Work out miles per gallon to litres per 100 km instantly with clear inputs, formula shown and shareable results.
mpg and L/100 km are reciprocals, so the same constant converts in both directions: divide it by the figure you have. For US gallons that constant is 235.214583; for Imperial gallons it is 282.480936. Because the operation is a division rather than a multiplication, the conversion is symmetric — running it twice returns the original number.
US gallons
L/100 km = 235.214583 ÷ mpg and mpg = 235.214583 ÷ L/100 km
Imperial gallons
L/100 km = 282.480936 ÷ mpg and mpg = 282.480936 ÷ L/100 km
On US gallons, 235.214583 ÷ 30 = 7.84 L/100 km. On Imperial gallons it is 282.480936 ÷ 30 = 9.42 L/100 km.
Because the two units are reciprocals. If y = k/x then x = k/y, so one constant and one division covers both directions.