For decades America ran on two slightly different feet
Until recently the United States used two feet. The international foot, fixed in 1959, is exactly 0.3048 metres; the older survey foot, kept for land mapping, is a hair longer. The gap is about an eighth of an inch per mile, but across state coordinate grids spanning hundreds of miles it mattered, so the survey foot was retired after 2022.
American customary units descend from the English measures in use before independence, themselves rooted in Roman and Anglo-Saxon practice. The United States standardised its version in 1832, but Britain had already reformed its own in 1824, creating imperial units from 1826. Because America skipped that overhaul, the two systems share names yet differ, especially in volume. The US gallon is the old pre-1824 wine gallon of 231 cubic inches, while the imperial gallon was redefined as the volume of 10 pounds of water, about a fifth larger. America also kept separate measures for liquids and for dry goods such as berries sold by the dry pint.
That split explains a few quirks. An old rhyme claims a pint's a pound the world around; that holds roughly for an American pint of water, which weighs about 4 percent more than a pound, but an imperial pint weighs a pound and a quarter. Barrels vary by cargo: 31 gallons for beer, 40 for whiskey, 42 for petroleum. The familiar 55-gallon drum is not a standard barrel at all. On nutrition labels, the teaspoon and tablespoon are quietly metric, exactly 5 and 15 millilitres.
Behind the scenes, customary units have been defined through the metre and kilogram since the Mendenhall Order of 1893. The Metric Conversion Act of 1975 declared metric the preferred system for trade, yet conversion was left voluntary and has stayed limited. Science, medicine and the military use metric; shops and building sites mostly do not. Some builders argue that feet and inches divide more neatly into halves, thirds and quarters.
Resistance once had a moral edge. In the late 19th century an institute for preserving traditional weights and measures cast the French system as atheistic, and one Ohio branch even published a song denouncing metric schemes.
Source: United States customary units
