The gallon is a
unit
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* ''Unit'' (a ...
of volume in
imperial units
The imperial system of units, imperial system or imperial units (also known as British Imperial or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed th ...
and
United States customary units. Three different versions are in current use:
*the imperial gallon (imp gal), defined as , which is or was used in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
,
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
,
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
,
Australia,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, and some
Caribbean countries;
*the US gallon (US gal), defined as , (231 cubic inches) which is used in the US and some
Latin America
Latin America or
* french: Amérique Latine, link=no
* ht, Amerik Latin, link=no
* pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived f ...
n and Caribbean countries; and
*the US dry gallon ("usdrygal"), defined as US
bushel
A bushel (abbreviation: bsh. or bu.) is an imperial and US customary unit of volume based upon an earlier measure of dry capacity. The old bushel is equal to 2 kennings (obsolete), 4 pecks, or 8 dry gallons, and was used mostly for agric ...
(exactly ).
There are two
pint
The pint (, ; symbol pt, sometimes abbreviated as ''p'') is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one eighth of a gallon. The British impe ...
s in a quart and four
quart
The quart (symbol: qt) is an English unit of volume equal to a quarter gallon. Three kinds of quarts are currently used: the liquid quart and dry quart of the US customary system and the of the British imperial system. All are roughly equ ...
s in a gallon. Different sizes of pints account for the different sizes of the imperial and US gallons.
The IEEE standard symbol for both US (liquid) and imperial gallon is gal, not to be confused with the
gal (symbol: Gal), a
CGS unit of
acceleration
In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...
.
Definitions
The gallon currently has one definition in the imperial system, and two definitions (liquid and
dry) in the US customary system. Historically, there were many definitions and redefinitions.
English system gallons
There were a number of systems of liquid measurements in the United Kingdom prior to the 19th century.
*
Winchester or corn gallon was (1697 Act 8 & 9 Will III c22)
**Henry VII (Winchester) corn gallon from 1497 onwards was
**Elizabeth I corn gallon from 1601 onwards was
**William III corn gallon from 1697 onwards was
*Old English (Elizabethan) ale gallon was (1700 Act 11 Will III c15)
*Old English (Queen Anne)
wine gallon A wine gallon is a unit of capacity that was used routinely in England as far back as the 14th century, and by statute under Queen Anne since 1707. Britain abandoned the wine gallon in 1826 when it adopted imperial units for measurement. The 1707 w ...
was standardized as in the 1706 Act 5 Anne c27, but it differed before that:
**London 'Guildhall' gallon (before 1688) was
**Jersey gallon (from 1562 onwards) was
**Guernsey gallon (17th century origins till 1917) was
*Irish gallon was (1495 Irish Act 10 Hen VII c22 confirmed by 1736 Act Geo II c9)
Imperial gallon
![Shell petrol station in the UK](https://upload.wikimedia.org/wikipedia/commons/0/04/Shell_petrol_station_in_the_UK.jpg)
The British imperial gallon is defined as exactly 4.54609 dm
3.
It is used in some
Commonwealth countries, and until 1976 was defined as the volume of 10 pounds (4.5359237 kg) of water at .
There are four quarts in a gallon, the
imperial pint
The pint (, ; symbol pt, sometimes abbreviated as ''p'') is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one eighth of a gallon. The British impe ...
is defined as 0.56826125 litres ( gallon) and there are 20 imperial
fluid ounce
A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume (also called ''capacity'') typically used for measuring liquids. The British Imperial, the United States customary, and the United ...
s in an imperial pint,
[ yielding 160 fluid ounces in an imperial gallon.
]
US liquid gallon
The US liquid gallon (frequently called simply "gallon") is legally defined as 231 cubic inch
The cubic inch (symbol in3) is a unit of volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its three dimensions (length, width, and height) being one inch long which is equivalent ...
es, which is exactly . A US liquid gallon can contain about of water at , and is about 16.7% less than the imperial gallon. There are four quart
The quart (symbol: qt) is an English unit of volume equal to a quarter gallon. Three kinds of quarts are currently used: the liquid quart and dry quart of the US customary system and the of the British imperial system. All are roughly equ ...
s in a gallon, two pint
The pint (, ; symbol pt, sometimes abbreviated as ''p'') is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one eighth of a gallon. The British impe ...
s in a quart and 16 US fluid ounces in a US pint
The pint (, ; symbol pt, sometimes abbreviated as ''p'') is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one eighth of a gallon. The British impe ...
, which makes the US fluid ounce equal to of a US gallon. In order to overcome the effects of expansion and contraction with temperature when using a gallon to specify a quantity of material for purposes of trade, it is common to define the temperature at which the material will occupy the specified volume. For example, the volume of petroleum products and alcoholic beverages are both referenced to in government regulations.
US dry gallon
Since the dry measure is one-eighth of a US '' Winchester'' bushel
A bushel (abbreviation: bsh. or bu.) is an imperial and US customary unit of volume based upon an earlier measure of dry capacity. The old bushel is equal to 2 kennings (obsolete), 4 pecks, or 8 dry gallons, and was used mostly for agric ...
of cubic inches, it is equal to exactly 268.8025 cubic inches, which is . The US dry gallon is not used in commerce, and is also not listed in the relevant statute, which jumps from the dry pint to the bushel.[''Authorized tables''](_blank)
', US Code'', Title 15, ch. 6, subchapter I, sec. 205, accessed 19 July 2008.
Worldwide usage
Imperial gallon
As of 2021, the imperial gallon continues to be used as the standard petrol unit in four British Overseas Territories (Anguilla
Anguilla ( ) is a British Overseas Territory in the Caribbean. It is one of the most northerly of the Leeward Islands in the Lesser Antilles, lying east of Puerto Rico and the Virgin Islands and directly north of Saint Martin. The terr ...
, the British Virgin Islands
)
, anthem = "God Save the King"
, song_type = Territorial song
, song = " Oh, Beautiful Virgin Islands"
, image_map = File:British Virgin Islands on the globe (Americas centered).svg
, map_caption =
, mapsize = 290px
, image_map2 = Bri ...
, the Cayman Islands, and Montserrat) and six countries ( Antigua and Barbuda, Dominica, Grenada, Saint Christopher and Nevis
Saint Kitts and Nevis (), officially the Federation of Saint Christopher and Nevis, is an island country and microstate consisting of the two islands of Saint Kitts and Nevis, both located in the West Indies, in the Leeward Islands chain of ...
, Saint Lucia, and Saint Vincent and the Grenadines
Saint Vincent and the Grenadines () is an island country in the Caribbean. It is located in the southeast Windward Islands of the Lesser Antilles, which lie in the West Indies at the southern end of the eastern border of the Caribbean Sea w ...
).
All of the countries and territories which use the imperial gallon as their petrol unit also use miles per hour
Miles per hour (mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour. It is used in the United Kingdom, the United States, and a number of smaller cou ...
for speed limits, and drive on the left side of the road.
The United Arab Emirates ceased selling petrol by the imperial gallon in 2010 and switched to the litre, with Guyana following suit in 2013.
Burma
Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
subsequently switched from the imperial gallon to the litre in 2014.
Antigua and Barbuda has proposed switching to selling petrol by litres since 2015.
The gallon was removed from the list of legally defined primary units of measure catalogued in the EU directive 80/181/EEC for trading and official purposes, with effect from 31 December 1994. Under the directive the gallon could still be used, but only as a supplementary or secondary unit. One of the effects of this directive was that the United Kingdom amended its own legislation to replace the gallon with the litre as a primary unit of measure in trade and in the conduct of public business, effective from 30 September 1995. However within the United Kingdom and Ireland, barrels and large containers of beer, oil and other fluids are commonly in multiples of an imperial gallon.
Ireland also passed legislation in response to the EU directive, with the effective date being 31 December 1993. Though the gallon has ceased to be a primary unit of trade, it can still be legally used in both the UK and Ireland as a supplementary unit.
Miles per imperial gallon is used as the primary fuel economy unit in the United Kingdom and as a supplementary unit in Canada on official documentation.
In the Middle East, water-chiller bottles come in multiples of the imperial gallon.
US liquid gallon
Other than the United States, petrol
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
is sold by the US gallon in Belize
Belize (; bzj, Bileez) is a Caribbean and Central American country on the northeastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a wate ...
, Colombia, Dominican Republic
The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares with ...
, Ecuador
Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ' ...
, Guatemala, Haiti, Honduras, Nicaragua
Nicaragua (; ), officially the Republic of Nicaragua (), is the largest country in Central America, bordered by Honduras to the north, the Caribbean to the east, Costa Rica to the south, and the Pacific Ocean to the west. Managua is the countr ...
, and Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = National seal
, national_motto = "Firm and Happy f ...
, as well as in the Marshall Islands
The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Intern ...
, Federated States of Micronesia
The Federated States of Micronesia (; abbreviated FSM) is an island country in Oceania. It consists of four states from west to east, Yap, Chuuk, Pohnpei and Kosraethat are spread across the western Pacific. Together, the states comprise a ...
, and Palau
Palau,, officially the Republic of Palau and historically ''Belau'', ''Palaos'' or ''Pelew'', is an island country and microstate in the western Pacific. The nation has approximately 340 islands and connects the western chain of the ...
, which are associated Associated may refer to:
*Associated, former name of Avon, Contra Costa County, California
* Associated Hebrew Schools of Toronto, a school in Canada
*Associated Newspapers, former name of DMG Media, a British publishing company
See also
*Associati ...
with the United States, and Liberia, a former protectorate
A protectorate, in the context of international relations, is a state that is under protection by another state for defence against aggression and other violations of law. It is a dependent territory that enjoys autonomy over most of its int ...
of the United States.
Despite its status as a US territory, and unlike American Samoa
American Samoa ( sm, Amerika Sāmoa, ; also ' or ') is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the island country of Samoa. Its location is centered on . It is east of the Internationa ...
, the Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands (CNMI; ch, Sankattan Siha Na Islas Mariånas; cal, Commonwealth Téél Falúw kka Efáng llól Marianas), is an unincorporated territory and commonw ...
, Guam
Guam (; ch, Guåhan ) is an organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. It is the westernmost point and territory of the United States (reckoned from the geographic cent ...
, and the US Virgin Islands
The United States Virgin Islands,. Also called the ''American Virgin Islands'' and the ''U.S. Virgin Islands''. officially the Virgin Islands of the United States, are a group of Caribbean islands and an unincorporated and organized territory ...
, Puerto Rico
Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
ceased selling petrol by the US gallon in 1980.
Panama
Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Co ...
ceased selling petrol in US gallons in 2013 and now uses litres, while El Salvador followed suit in June 2021.
In the Turks and Caicos Islands
The Turks and Caicos Islands (abbreviated TCI; and ) are a British Overseas Territory consisting of the larger Caicos Islands and smaller Turks Islands, two groups of tropical islands in the Lucayan Archipelago of the Atlantic Ocean and n ...
, both the US gallon and imperial gallon are used due to an increase in tax duties which was disguised by levying the same duty on the US gallon (3.79 L) as was previously levied on the Imperial gallon (4.55 L).
The Bahamas
The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the ar ...
also uses both the US gallon and imperial gallon.
Relationship to other units
Both the US liquid and imperial gallon are divided into four quarts (''quart''er gallons), which in turn are divided into two pint
The pint (, ; symbol pt, sometimes abbreviated as ''p'') is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one eighth of a gallon. The British impe ...
s, which in turn are divided into two cups
CUPS (formerly an acronym for Common UNIX Printing System) is a modular printing system for Unix-like computer operating systems which allows a computer to act as a print server. A computer running CUPS is a host that can accept print jobs ...
, (not in customary use outside the US), which in turn are further divided into two gills
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
. Thus, both gallons are equal to four quarts, eight pints, sixteen cups, or thirty-two gills.
The imperial gill is further divided into five fluid ounces, whereas the US gill is divided into four fluid ounces, meaning an imperial fluid ounce is of an imperial pint, or of an imperial gallon, while a US fluid ounce is of a US pint, or of a US gallon. Thus, the imperial gallon, quart, pint, cup and gill are approximately 20% larger than their US counterparts, meaning these are not interchangeable, but the imperial fluid ounce is only approximately 4% smaller than the US fluid ounce, meaning these are often used interchangeably.
Historically, a common bottle size for liquor in the US was the " fifth", i.e. one-fifth of a US gallon (or one-sixth of an imperial gallon). While spirit sales in the US were switched to metric measures in 1976, a 750 mL bottle is still sometimes known as a "fifth".
History
The term derives most immediately from ''galun'', ''galon'' in Old Norman French
Old Norman, also called Old Northern French or Old Norman French ( fro, Ancien Normant, nrf, Ancien Normaund), was one of many varieties of the '' langues d'oïl'' native to northern France. It was spoken throughout the region of what is now call ...
, but the usage was common in several languages, for example in Old French
Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intellig ...
and (bowl) in Old English. This suggests a common origin in Romance Latin, but the ultimate source of the word is unknown.
The gallon originated as the base of systems for measuring wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
and beer
Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
in England. The sizes of gallon used in these two systems were different from each other: the first was based on the wine gallon A wine gallon is a unit of capacity that was used routinely in England as far back as the 14th century, and by statute under Queen Anne since 1707. Britain abandoned the wine gallon in 1826 when it adopted imperial units for measurement. The 1707 w ...
(equal in size to the US gallon), and the second one either the ale gallon or the larger imperial gallon.
By the end of the 18th century, there were three definitions of the gallon in common use:
*The ''corn gallon'', or ''Winchester gallon'', of about ,
*The ''wine gallon A wine gallon is a unit of capacity that was used routinely in England as far back as the 14th century, and by statute under Queen Anne since 1707. Britain abandoned the wine gallon in 1826 when it adopted imperial units for measurement. The 1707 w ...
'', or '' Queen Anne's gallon'', which was , and
*The ''ale gallon'' of .
The ''corn'' or ''dry gallon'' is used (along with the dry quart and pint) in the United States for grain and other dry commodities. It is one-eighth of the (Winchester) bushel, originally defined as a cylindrical measure of inches in diameter and 8 inches in depth, which made the dry gallon )2 × ≈ 2150.42017 cubic inches. The bushel was later defined to be 2150.42 cubic inches exactly, thus making its gallon exactly (); in previous centuries, there had been a corn gallon of between 271 and 272 cubic inches.
The ''wine'', ''fluid'', or ''liquid gallon'' has been the standard US gallon since the early 19th century. The wine gallon, which some sources relate to the volume occupied by eight medieval merchant pounds of wine, was at one time defined as the volume of a cylinder 6 inches deep and 7 inches in diameter, i.e. . It was redefined during the reign of Queen Anne in 1706 as 231 cubic inches exactly, the earlier definition with approximated to .
:
Although the wine gallon had been used for centuries for import duty purposes, there was no legal standard of it in the Exchequer
In the civil service of the United Kingdom, His Majesty’s Exchequer, or just the Exchequer, is the accounting process of central government and the government's '' current account'' (i.e., money held from taxation and other government revenu ...
, while a smaller gallon was actually in use, requiring this statute; it remains the US definition today.
In 1824, Britain adopted a close approximation to the ''ale gallon'' known as the ''imperial gallon'', and abolished all other gallons in favour of it. Inspired by the kilogram-litre relationship, the imperial gallon was based on the volume of 10 pounds of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury
Inch of mercury (inHg and ″Hg) is a non- SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States.
It is the pressure exerted by a column of mercury in heigh ...
and at a temperature of .
In 1963, this definition was refined as the space occupied by 10 pounds of distilled water of density weighed in air of density against weights of density (the original "brass" was refined as the densities of brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...
alloys vary depending on metallurgical composition), which was calculated as to ten significant figures.
The precise definition of exactly cubic decimetres (also , ≈ ) came after the litre was redefined in 1964. This was adopted shortly afterwards in Canada, and adopted in 1976 in the United Kingdom.
Sizes of gallons
Historically, gallons of various sizes were used in many parts of Western Europe. In these localities, it has been replaced as the unit of capacity by the litre
The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3 ...
.
References
External links
{{systems of measurement, sp=us
Customary units of measurement in the United States
Imperial units
Systems of units
Units of volume
Alcohol measurement
Cooking weights and measures