Fuel economy is the relationship between distance traveled and the amount of fuel that is used. The miles that can be traveled off of one gallon of gas is called miles per gallon (MPG).
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 80000 Quantities and Units, so the nationally-defined reciprocal quantities fuel economy and fuel consumption are used in this article. The two most common ways to measure automobile fuel usage are: Fuel economy and fuel consumption are reciprocal quantities. To convert either way between L/100_km and miles per US gallon, divide 235 by the number in question; for miles per imperial gallon, divide 282 by either number. For example, to convert from 30_mpg to L/100_km, divide 235 by 30, giving 7.83_L/100_km; or from 10 L/100_km to mpg (US), divide 235 by 10, giving 23.5_mpg. To convert between L/100_km and km/L, divide 100 by the number in question. A related measure is the amount of carbon dioxide produced as a result of the combustion process, typically measured in grams of CO2 per kilometre (CO2 g/km). A petrol (gasoline) engine will produce around 2.32_kg of carbon dioxide for each litre of petrol consumed (19.4_lb/gal). A typical diesel engine
Contributions by David R. Ingham, Mrzaius, and BenFrantzDale.