Fuel efficiency

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Fuel efficiency, sometimes also referred to as fuel economy and commonly gas mileage in the United States, is a numeric measure often used to describe the amount of fuel consumed with regard to the distance travelled in a transportation vehicle, such as an automobile.

The measure is usually expressed in two ways:

As the amount of fuel used per unit distance; for example, litres per 100 kilometres (l/100 km). In this case, the lower the value the more efficient a vehicle is;
As the distance travelled per unit volume of fuel used; for example, kilometres per litre (km/l) or miles per gallon (mpg). In this case, the higher the value the more efficient a vehicle is.

Here are some common conversion factors:

To convert x l/100 km to y mpg, perform:

235.2146 ÷ x l/100 km = y mpg (US liquid gallon), or
282.481 ÷ x l/100 km = y mpg (Imperial gallon)

To convert a mpg to b l/100 km, perform:

235.2146 ÷ a mpg (US liquid gallon) = b l/100 km, or
282.481 ÷ a mpg (Imperial gallon) = b l/100 km

To convert m km/l to n mpg, perform:

2.352146 * m km/l = n mpg (US liquid gallon), or
2.82481 * m km/l = n mpg (Imperial gallon)

To convert c mpg to d km/l, perform:

0.4251437 * c mpg (US liquid gallon) = d km/l, or
0.354006 * c mpg (Imperial gallon) = d km/l