The History of Fuel Economy Measurement
The Horse as the Benchmark
Before cars, transport efficiency was measured in terms of horses — how far could a horse travel on how much feed? James Watt defined 'horsepower' in 1782 to help sell steam engines by comparing them to the horses they replaced. This gave people an intuitive reference for engine power that we still use today.
Early Automobiles: No One Cared
When cars first appeared in the 1880s and 1890s, fuel efficiency was irrelevant — gasoline was cheap and plentiful, and the main concern was simply making the engines work. Early motorists were wealthy adventurers for whom cost was no object. Fuel consumption wasn't even tracked systematically.
Miles Per Gallon Emerges
As cars became mass-market products in the 1920s and 30s, manufacturers began advertising fuel economy as a selling point. 'Miles per gallon' (MPG) became standard in the US and UK because it expressed something consumers instinctively understood: more miles for the same gallon of gas = better value.
The 1973 Oil Crisis Changes Everything
The 1973 OPEC oil embargo sent gasoline prices skyrocketing and caused massive shortages. For the first time, fuel economy became a national priority. The US Congress passed the Energy Policy Conservation Act (1975), creating Corporate Average Fuel Economy (CAFE) standards — the first legal fuel efficiency requirements for automakers.
L/100km vs. MPG
Most of the world uses liters per 100 kilometers (L/100km) — a 'consumption' metric where lower is better. The US and UK use MPG — an 'efficiency' metric where higher is better. The two scales are not linear inverses of each other: improving from 10 to 20 MPG saves far more fuel than improving from 40 to 50 MPG, a fact that L/100km makes immediately obvious.
The Electric Era
Electric vehicles use 'MPGe' (miles per gallon equivalent) in the US — how far the vehicle travels on the energy equivalent of one gallon of gasoline (33.7 kWh). In most of the world, EV efficiency is measured in kWh per 100 km. As EVs become mainstream, these new metrics are slowly becoming as familiar as MPG once was.