What does gallon mean?
A gallon is a unit of volume used almost exclusively for measuring liquids, most familiar today as the container size of milk or gasoline sold in American stores and pumps. Two versions exist: the US gallon, standardized at about 3.785 liters, and the older British imperial gallon, at about 4.546 liters — a difference large enough to cause genuine confusion in trade and travel. The term appears constantly in daily American life, whether describing a recipe calling for half a gallon of cream, a water heater rated in gallons, or a car's efficiency expressed in miles per gallon. Though much of the world has adopted metric units, the gallon endures as a deeply embedded customary measure, and understanding it remains useful for reading American prices, recipes, and fuel economy figures.
nounA unit of volume for liquid measure equal to eight pints, now standardized as 3.785 liters in the US and 4.546 liters in the UK.
- A unit of liquid volume equal to 3.785 liters (US gallon), used chiefly in the United States.
- A unit of liquid volume equal to 4.546 liters (imperial gallon), formerly standard in the United Kingdom and Commonwealth countries.
"The car gets forty miles to the gallon on the highway."
"We bought a gallon of milk at the store this morning."
"The tank holds fifty gallons of water, enough for several days."
The plural follows regular English noun inflection; the abbreviation 'gal' is used in technical and commercial contexts.
"The barrel held over thirty gallons of oil."
The US and UK both call it a "gallon," but their gallons differ by nearly a liter — an imperial gallon holds about a fifth more.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of gallon
The word gallon entered Middle English from Anglo-Norman French, deriving ultimately from medieval Latin forms such as galleta or galletum, meaning a jug or cask and later a liquid measure. Its exact deeper origins are uncertain, though a Celtic root has been suggested without firm evidence. The same French source gave rise to galloon, a term for braided trim on clothing, showing how one medieval word branched into both measurement and decoration. The English spelling settled into its modern form by the late medieval period, and the unit was later formally defined differently in Britain and America.
Related word forms
How gallon is actually used
The word is common in everyday speech in the United States, where the US gallon remains the standard household measure for milk, gasoline, and other liquids. In the UK, the imperial gallon has officially been replaced by the liter, though it survives in informal use and in fuel-consumption figures quoted in miles per gallon. Because the two gallons differ substantially in size, international contexts should specify which gallon is meant.
Easily confused with gallon
A galleon is a large sailing ship used especially from the 15th to 17th centuries, while a gallon is a unit of liquid volume.