Miles per gallon is a horrendous unit of measurement for this exact reason. Trips are of fixed length, and you generally want to calculate fuel usage for those

Miles per gallon is a horrendous unit of measurement for this exact reason. Trips are of fixed length, and you generally want to calculate fuel usage for those trips. MPG is useful for comparing what sort of trips you can take with a fixed amount of fuel, which describes approximately zero real-world situations. The overwhelming majority of calculations involving MPG require you to take the reciprocal first. Like, the "average" for average fuel economy of different cars is the harmonic mean. It's silly. Gah.