galun

The word gallon entered English from Old Northern French galun or jalon, meaning a liquid measure or a bowl. The deeper origin is uncertain. Some etymologists trace it to Medieval Latin galleta, a pail or bucket. Others connect it to Gaulish roots. What is clear is that by the thirteenth century, English merchants were using 'gallon' to name a specific quantity of liquid, and that quantity was anything but specific.

Medieval England had several gallons in simultaneous use. The wine gallon, the ale gallon, and the corn gallon all named different volumes. The wine gallon was approximately 231 cubic inches. The ale gallon was larger. Merchants argued about which applied to which commodity. In 1824, the British Imperial system standardized the gallon at 277.42 cubic inches — the volume occupied by ten pounds of water at a specific temperature. This was the corn gallon, roughly, and it was larger than any previous wine gallon.

The American gallon took a different path. When the United States adopted its system of measures in 1836, it kept the old Queen Anne wine gallon of 231 cubic inches, defined in 1706. The result is a transatlantic confusion that persists to this day: an American gallon is about 3.785 litres, a British gallon about 4.546 litres. A gallon of milk in London holds twenty percent more milk than a gallon in New York.

The metric system has replaced the gallon in most countries, but the United States continues to sell gasoline, milk, and paint by the gallon. The word itself — from a French word for a bowl — has outlasted every attempt to standardize the thing it names. The bowl has been the same word for eight hundred years. Its size has never been settled.