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# Fuel efficiency

Fuel efficiency, sometimes also referred to as fuel economy, 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:

1. 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;
2. 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