Fuel efficiency is a measurement of how much fuel it takes to power a vehicle for a certain distance. In the United States, this is usually stated as miles per gallon. However, in other parts of the world, the Metric system is more commonly used. A common metric unit of volume for fluid is the litre. If you want to measure miles per litre, you only need to perform a few simple mathematical calculations.

Fill up your gas tank and write down your current mileage.

Drive until the gas tank is reading half full or less.

Fill your tank again. Write down how many gallons of fuel you put into the vehicle. Write down your new mileage as well.

Subtract the new mileage from the initial mileage and divide your answer by the number of gallons that you wrote down in step three. This will give you miles per gallon.

Divide your answer from step four by 3.785 to find miles per litre, since it takes 3.785 litres to equal one gallon. For instance, if your car gets 20 miles per gallon, divide 20 by 3.785 to get 5.284 miles per litre.