Gallon: the story on HearLore

Gallon

The gallon began as a measure for wine and ale in medieval England, but its origins are shrouded in the same confusion that plagued its evolution for centuries. Before the 18th century, there was no single gallon; instead, England used three distinct definitions simultaneously. The wine gallon, which eventually became the standard for the United States, was legally adopted in 1836 and defined as 231 cubic inches. This specific volume was historically linked to the weight of eight medieval merchants' pounds of wine, a cylinder six inches deep and seven inches in diameter. Meanwhile, the ale gallon was 1.65% larger than the modern imperial gallon, and the corn gallon, used for dry commodities like grain, was even larger still. These three systems coexisted until the British Parliament standardized the imperial gallon in 1824, defining it as the volume of 10 pounds of distilled water. This decision was not merely mathematical but a political act to unify a fractured system of trade and taxation that had varied by region and commodity for hundreds of years.

The Great Divergence

The split between the imperial gallon and the US gallon is a story of geography and timing, resulting in two units that share a name but differ by nearly 20 percent. The US gallon is legally defined as exactly 231 cubic inches, a standard established by the Wine Measure of 1706 during the reign of Queen Anne. This definition persisted in the United States after independence, while Britain moved toward a new standard. In 1824, Britain adopted the imperial gallon, defined as the volume of 10 pounds of distilled water at a specific temperature and pressure. This new imperial gallon was approximately 20 percent larger than the US wine gallon. The difference is compounded by the fluid ounce; an imperial fluid ounce is 20 percent larger than a US fluid ounce, and the imperial gallon contains 160 fluid ounces while the US gallon contains 128. This divergence means that a pint in the UK holds 20 fluid ounces, whereas a pint in the US holds only 16. The discrepancy creates practical confusion in international trade, where a barrel of oil or a case of beer might be measured differently depending on which side of the Atlantic the transaction occurs.

A Global Patchwork

Today, the gallon exists in a fragmented global landscape, surviving in pockets of the former British Empire and specific American territories. The imperial gallon remains the standard for petrol in four British Overseas Territories, including Anguilla and the Cayman Islands, and in four Caribbean nations such as Antigua and Barbuda and Saint Lucia. These eight jurisdictions share a unique cultural quirk: they drive on the left side of the road and use miles per hour for speed limits, yet they measure fuel in gallons. In contrast, the United States and its territories, including American Samoa and Guam, continue to use the US gallon for all liquid trade. The United Arab Emirates switched from the imperial gallon to the litre in 2010, and Guyana followed in 2013. Even more recently, the Dubai Electricity and Water Authority transitioned its water billing from imperial gallons to cubic metres in March 2025. The European Union removed the gallon from its list of primary units of measure in 1994, forcing countries like Ireland and the United Kingdom to adopt the litre for official trade, though the gallon persists as a supplementary unit for beer and oil. This patchwork of usage creates a complex map where a gallon in the Caribbean is not the same as a gallon in the United States, and neither matches the gallon that was standard in London until the 1970s.

Common questions

When was the wine gallon legally adopted in the United States?

The wine gallon was legally adopted in the United States in 1836. This standard was defined as 231 cubic inches and historically linked to the weight of eight medieval merchants pounds of wine. The specific volume formed a cylinder six inches deep and seven inches in diameter.

What is the difference between the imperial gallon and the US gallon?

The imperial gallon is approximately 20 percent larger than the US gallon. Britain adopted the imperial gallon in 1824 as the volume of 10 pounds of distilled water, while the US gallon remained 231 cubic inches. This divergence means an imperial fluid ounce is 20 percent larger than a US fluid ounce.

Which countries still use the imperial gallon for petrol today?

The imperial gallon remains the standard for petrol in four British Overseas Territories and four Caribbean nations. These jurisdictions include Anguilla, the Cayman Islands, Antigua and Barbuda, and Saint Lucia. These eight locations share a unique cultural quirk of driving on the left side of the road while measuring fuel in gallons.

When did the Dubai Electricity and Water Authority switch from imperial gallons to cubic metres?

The Dubai Electricity and Water Authority transitioned its water billing from imperial gallons to cubic metres in March 2025. This change followed similar moves by the United Arab Emirates in 2010 and Guyana in 2013. The European Union removed the gallon from its list of primary units of measure in 1994.

What was the volume of the US dry gallon and when was it replaced?

The US dry gallon was defined as one-eighth of a US Winchester bushel and equal to approximately 268.8 cubic inches. This measure was used for grain and other dry commodities until the 1990s. It was replaced by the peck and the bushel in modern trade and is no longer included in relevant statutes.

How did the fifth bottle size originate from the US gallon?

The standard bottle size for liquor in the United States was historically known as the fifth, which is one-fifth of a US gallon. This volume is approximately 757 milliliters and was slightly larger than a reputed quart. Although spirit sales in the US were officially switched to metric measures in 1976, the 750 milliliter bottle is still commonly referred to as a fifth by consumers and retailers.