When you're travelling in a country that sells fuel by the litre, you may wonder how many gallons you're using. You can easily convert litres per gallon to miles per gallon (mpg) to keep track of your fuel economy. Learn a few simple formulas and you can do the conversions in your head.

Multiply the number of litres of fuel you have used by 0.264 to find the equivalent in gallons. For example, 40 litres equals 10.56 gallons. (Divide the number of litres of fuel by 4 if you don't have a calculator and just want a rough estimate.)

Multiply the kilometres you have driven by 0.621 to find the equivalent in miles. For example, 60km equals 37.26 miles. (Divide the number of kilometres by 3 and multiply by 2 for a rough estimate in miles.)

Divide 235.2 by the number of litres per 100km to find the equivalent in mpg. There's no easy way to do this in your head, but you can remember a few key numbers: 15 litres per 100km equals about 15mpg, 10 litres per 100km equals about 23mpg and 7 litres per 100km equals about 33mpg.