Gallon

The gallon is a unit of measurement for volume and fluid capacity in both the US customary units and the British imperial systems of measurement. Three significantly different sizes are in current use:

  • the imperial gallon, defined as 4.54609 litres, which is used in the United Kingdom, Canada, and some Caribbean nations;
  • the US gallon defined as 231 cubic inches (exactly 3.785411784 litres), which is used in the US and some Latin American and Caribbean countries; and
  • the US dry gallon, defined as ​1⁄8 US bushel (exactly 4.40488377086 litres).

Gallon
A one-US-gallon gas can showing "U.S. gallon" marking (for US use), imperial gallons (for Canadian use), and litres
General information
Unit ofVolume
Symbolgal 
Conversions (imperial)
1 imp gal in ...... is equal to ...
   SI-compatible units   4.54609 L
   US customary units   ≈ 1.200950 US gal
   US customary units   ≈ 277.4194 in3
Conversions (US)
1 US gal in ...... is equal to ...
   SI-compatible units    3.785411784 L
   Imperial units   ≈ 0.8326742 imp gal
   Imperial units   231 in3
   US dry gallon   ≈ 0.859367 US dry gal

There are four quarts in a gallon and eight pints in a gallon, and they have different sizes in different systems.

The IEEE standard symbol for the gallon is gal.[1]

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.[2]

  • Winchester or Corn Gallon was 272 in3 (157 imp fl oz) (1697 Act 8 & 9 Will III c22)
    • Henry VII (Winchester) corn gallon from 1497 onwards was 154.80 fl oz
    • Elizabeth I corn gallon from 1601 onwards was 155.70 fl oz
    • William III corn gallon from 1697 onwards was 156.90 fl oz
  • Old English (Elizabethan) Ale Gallon was 282 in3 (163 imp fl oz) (1700 Act 11 Will III c15)
  • Old English (Queen Anne) Wine Gallon was standardized as 231 in3 (133 imp fl oz) in the 1706 Act 5 Anne c27, but it differed before that:
    • London 'Guildhall' gallon (before 1688) was 129.19 fl oz
    • Jersey gallon (from 1562 onwards) was 139.20 fl oz
    • Guernsey gallon (17th century origins till 1917) was 150.14 fl oz
  • Irish Gallon was 217 in3 (125 imp fl oz) (1495 Irish Act 10 Hen VII c22 confirmed by 1736 Act Geo II c9)

Imperial gallon
A Shell petrol station selling 2* and 4* (leaded petrol) by the gallon in the UK c. 1980

The British imperial gallon is now defined as exactly 4.54609 litres (277.4194 cubic inches).[3] It is used in some Commonwealth countries. Until 1976 it was based on the volume of 10 pounds (4.5359 kg) of water at 62 °F (17 °C).[4][5] There are four quarts in a gallon, the imperial pint is defined as 0.56826125 litres (i.e. 1/8 gallon) and there are 20 imperial fluid ounces in an imperial pint.[3]

US liquid gallon
A fuel station in the United States displaying fuel prices per US gallon

The US liquid gallon (frequently called simply "gallon") is legally defined as 231 cubic inches, which is exactly 3.785411784 litres.[6][7] A US liquid gallon of water weighs about 8.34 pounds or 3.78 kilograms at 62 °F (17 °C), making it about 16.6% lighter than the imperial gallon. There are four quarts in a gallon, two pints in a quart and 16 US fluid ounces in a US pint, which makes the US fluid ounce equal to 1/128 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[8] and alcoholic beverages[9] are both referenced to 60 °F (15.6 °C) in government regulations.

US dry gallon

Since the dry measure is one-eighth of a US Winchester bushel of 2150.42 cubic inches, it is therefore equal to exactly 268.8025 cubic inches, which is 4.40488377086 L.[10] 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.[11]

Worldwide usage of gallons

Gallons used in fuel economy expression in Canada and the United Kingdom are imperial gallons.[12][13]

Despite its status as a U.S. territory, and unlike American Samoa,[14] the Northern Mariana Islands,[15] Guam,[16] and the U.S. Virgin Islands,[17] Puerto Rico ceased selling gasoline by the US gallon in 1980.[18]

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.[19] 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.[20][21][22]

Ireland also passed legislation in response to the EU directive, with the effective date being 31 December 1993.[23] Though the gallon has ceased to be the legally defined primary unit, it can still be legally used in both the UK and Ireland as a supplementary unit.

The United Arab Emirates started selling gasoline by the litre in 2010,[24] while Guyana[25] and Panama switched in 2013.[26] The UAE and Guyana, former British colonies, had used the imperial gallon and Panama the US gallon before this time.[27]

Myanmar (Burma) switched from imperial gallon to litre sales before 2014.[28]

Antigua and Barbuda planned to switch over to using litres by 2015,[29] but due to various issues, the switch-over was only effected in 2019.

As of 2019, the imperial gallon continues to be used as a unit of measure in Anguilla,[30] the British Virgin Islands,[31] the Cayman Islands,[32] Dominica,[33] Grenada,[34] Montserrat,[35][36] St. Kitts & Nevis,[37] St. Lucia,[38] and St. Vincent & the Grenadines.[39]

Other than the United States, the US gallon is still used in Belize, Colombia, The Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Liberia, Nicaragua, and Peru, but only for the sale of gasoline; all other products in these countries are sold in litres, or multiples and submultiples of a litre.[27]

In the Turks & Caicos Islands, both the U.S. gallon and imperial gallon are used. This is due to an increase in tax duties which was disguised by levying the same duty on the U.S. gallon (3.79 L) as was previously levied on the Imperial gallon (4.55 L).[40]

Relationship to other units

Both the US liquid and imperial gallon are divided into four quarts (quarter gallons), which in turn are divided into two pints, which in turn are divided into two cups, which in turn are further divided into two gills. 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 1/20 of an imperial pint, or 1/160 of an imperial gallon, while a US fluid ounce is 1/16 of a US pint, or 1/128 of a US gallon. Since the imperial gallon, quart, pint, cup and gill are approximately 20% larger than their US counterparts, these are not interchangeable, while the imperial fluid ounce is only approximately 4% smaller than the US fluid ounce, and they are often therefore 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".[41][42]

History

The term derives most immediately from galun, galon in Old Northern French, but the usage was common in several languages, for example jale in Old French and gęllet (bowl) in Old English. This suggests a common origin in Romance Latin, but the ultimate source of the word is unknown.[43]

The gallon originated as the base of systems for measuring wine and beer in England. The sizes of gallon used in these two systems were different from each other: the first was based on the wine gallon (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 268.8 cubic inches (≈ 4.405 L),
  • The wine gallon, or Queen Anne's gallon, which was 231 cubic inches[44] (≈ 3.785 L), and
  • The ale gallon of 282 cubic inches (≈ 4.622 L).

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 18+1/2 inches in diameter and 8 inches in depth, which made the dry gallon 8 in × (9+1/4 in)2 × π ≈ 2150.42017 cubic inches. The bushel was later defined to be 2150.42 cubic inches exactly, thus making its gallon exactly 268.8025 in3 (4.40488377086 L); 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. 6 in × (3+1/2 in)2 × π ≈ 230.907 06 cubic inches. It was redefined during the reign of Queen Anne in 1706 as 231 cubic inches exactly, the result of the earlier definition with π approximated to 22/7. Although the wine gallon had been used for centuries for import duty purposes, there was no legal standard of it in the Exchequer, and a smaller gallon (224 cu in) was actually in use, meaning this statute became necessary; 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 and at a temperature of 62 °F.

In 1963, this definition was refined as the space occupied by 10 pounds of distilled water of density 0.998859 g/mL weighed in air of density 0.001217 g/mL against weights of density 8.136 g/mL (the original "brass" was refined as the density of brass alloys vary depending on metallurgical composition), which was calculated as 4.546091879 L to ten significant figures.[4]

The precise definition of exactly 4.54609 cubic decimetres (also 4.54609 L, ≈ 277.419433 in3) came after the litre was redefined in 1964. This was adopted shortly afterwards in Canada, and adopted in 1976 in the United Kingdom.[4]

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.

Comparison of current gallons
Volume Definition Inverted volume
(gallons per cubic foot)		 Approx.
weight of
water (pounds
per gallon
@ 62 °F)		 Cylindrical approximation
(cu in)(L or dm3) Diameter
(in)		Height
(in)		Relative
error (%)
2313.785411784 statute of 5th of Queen Anne (UK wine gallon, standard US gallon) 7.488.33 760.04
268.80254.40488377086 Winchester, statute 13 + 14 by William III (corn gallon, US dry gallon) 6.439.71 18.510.00001
≈ 277.41944.54609 standard imperial gallon (metric; adopted 1964 in Canada, 1976 in UK) ≈ 6.2310 5⅔110.0002
Comparison of historic gallons
Volume Definition Inverted volume
(gallons per cubic foot)		 Approx.
weight of
water (pounds
per gallon
@ 62 °F)		 Cylindrical approximation
(cu in)(L or dm3) Diameter
(in)		Height
(in)		Relative
error (%)
216 (Roman unciae)≈ 3.53961 Roman congius 87.8 5110.01
224≈ 3.67070 preserved at the Guildhall, London (old UK wine gallon) 7.718.09 93.50.6
264.8≈ 4.33929 ancient Rumford quart (1228) 6.539.57 7.560.1
265.5≈ 4.35077 Exchequer (Henry VII, 1497, with rim) 6.519.59 1320.01
266.25≈ 4.36306 ancient Rumford (1228)       
271≈ 4.44089 Exchequer (1601, E.) (old corn gallon) 6.389.79 4.5170.23
272≈ 4.45728 corn gallon (1688)       
≈ 277.2026≈ 4.54254 statute 12 of Anne (coal gallon) = 33/32 corn gallons 6.2310    
≈ 277.274≈ 4.54370Imperial Gallon, as originally determined in 1824 6.2310    
≈ 277.41954.546091879 Imperial gallon as re-determined in 1895 and defined in 1963 ≈ 6.2310    
278≈ 4.55560 Exchequer (Henry VII, with copper rim) 6.2110.04    
278.4≈ 4.56216 Exchequer (1601 and 1602 pints) 6.2110.06    
280≈ 4.58838 Exchequer (1601 quart) 6.1710.1    
282≈ 4.62115 Treasury (beer and ale gallon pre-1824) 6.1310.2    

References
  1. IEEE Std 260.1-2014
  2. Ricketts, Carl. "Capacity Measures of the British Isles" (PDF). Retrieved 6 September 2016.
  3. "Weights and Measures Act 1985, chapter 72, schedule 1". legislation.gov.uk. The National Archives on behalf of HM Government. Retrieved 7 June 2019.
  4. BS 350:Part 1:1974 Conversion factors and tables Part 1. Basis of tables. Conversion factors (AMD 4153 ed.). British Standards Institution. 1983. p. Foreword. Before that date (November 1976) the definition in the Weights and Measures Act 1963 was such that the gallon could be calculated to be 4.546 091 879 dm3 to ten significant figures ... The return, in November 1976, by precise definition to what had earlier been used as an approximation for the value of the gallon (i.e. 4.546 09 dm3)...
  5. BS 350:Part 1:1974 Conversion factors and tables Part 1. Basis of tables. Conversion factors (prior to Amendment No.1 1983 ed.). British Standards Institution. 1974. p. 10. the UK gallon (UKgal), defined in Schedule 1 of the Weights and Measures Act 1963, as the space occupied by 10 pounds weight of distilled water under certain conditions specified in the schedule.
  6. "NIST Handbook 44 - 2012 Edition Appendix C "General Tables of Units of Measurement"". p. C-5.
  7. Uniform Laws and Regulations in the areas of legal metrology and engine fuel quality (PDF). US Department of Commerce, National Institute of Standards and Technology. 2011. pp. 9–13, 69.
  8. State of New Hampshire Dept of Weights and Measure Archived 13 April 2012 at the Wayback Machine
  9. 27 CFR section 5.21
  10. "US Dry Conversion Calculator". High accuracy calculation for life or science. Retrieved 24 October 2019.
  11. Authorized tables, US Code, Title 15, ch. 6, subchapter I, sec. 205, accessed 19 July 2008.
  12. "FAQs – Fuel Consumption Program". Transport Canada. 5 November 2008. Archived from the original on 20 May 2010. Retrieved 31 July 2018.
  13. Statutory Instrument 2001/3523 Environmental Protection - The Passenger Car (Fuel Consumption and CO2 Emissions Information) Regulations 2001 (PDF). The Stationery Office. 30 October 2001. ISBN 0-11-038743-0. Retrieved 1 December 2011.
  14. "Gasoline goes up eleven cents per gallon tomorrow". Samoa News. Archived from the original on 4 March 2016.
  15. Dones, Liberty (17 May 2006). "Shell pump prices up 8 cents". Saipan Tribune. Archived from the original on 30 October 2006. Retrieved 30 September 2013.
  16. "UPDATE: Gas prices down 10 cents to $4.73 for a gallon of unleaded". Pacific Daily News. Archived from the original on 30 September 2013.
  17. Blackburn, Joy (16 July 2012). "7-cent-per-gallon WAPA tax goes into effect". Virgin Islands Daily News. Archived from the original on 30 September 2013.
  18. Pesquera de Busquets, Carmen T; Barcelo, Carlos Romero (14 June 1979). "Order to establish the price of half (1/2) galon [sic] of gasoline as transitory measure and that the litter [sic] should be the final metric measurement for the sale of gasoline in Puerto Rico" (PDF). San Juan, Puerto Rico: Departamento de Asuntos del Consumidor. Retrieved 21 May 2013. Cite journal requires |journal= (help)
  19. The Council of the European Communities (9 February 2000). "Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC". Retrieved 7 February 2009. The legal units of measurement ... for economic, public health, public safety or administrative purposes ... litre
  20. "The Units of Measurement Regulations 1995 (Article 4)". 13 July 1995. Retrieved 1 December 2011.
  21. "Units of Measurement Directive". LACORS. 1995. Archived from the original on 24 April 2012. Retrieved 26 November 2011.
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  23. "S.I. No. 255/1992 — European Communities (Units of Measurement) Regulations, 1992". Irish Statute Book. Office of the Attorney General. 9 September 1992. Retrieved 1 December 2011.
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  28. "Petrol Prices March 2014 in Yangon, Myanmar".
  29. "The Re-Launch of Antigua And Barbuda's Metrication Programme". Diversity Global Magazine. 2013. Archived from the original on 16 January 2012. Retrieved 20 May 2013.
  30. "Anguilla Renewable Energy Integration Project Final Report" (PDF). Anguilla RE Integration Final Report. Government of Anguilla Ministry of Infrastructure, Communications, Utilities, and Housing (MICUH). 19 October 2012. p. 104. Retrieved 13 October 2013. In 2008—the most recent year where WTI crude oil averaged US$100 per barrel—ANGLEC paid an average of about US$4 per imperial gallon (IG) for diesel.
  31. Walker, William (5 September 2012). "Biwater project draws scrutiny". Archived from the original on 2 October 2013. Retrieved 30 September 2013.
  32. Wilson, Stuart (9 May 2013). "Fuel costs driven by factors". Cayman Compass.
  33. "Photo of the day: Up and up it goes". Dominica News Online. 10 May 2011.
  34. Grenada: Third Review Under the Three-Year Arrangement Under the Poverty Reduction and Growth Facility, Requests for Modification of Quantitative Performance Criterion and Augmentation, and Financing Assurances Review. International Monetary Fund. 2009. p. 17. Retrieved 13 October 2013.
  35. "Gasoline price increases, diesel decreases, cost of living goes up". The Montserrat Reporter. 30 November 2012.
  36. Htin Lynn Aung (22 September 2017). "Fuel prices on the rise". The Myanmar Times.
  37. Thomas, Steve (5 September 2008). "Gas prices capped under $18 – lowest since July". The St. Kitts-Nevis Observer. Archived from the original on 24 May 2012.
  38. "Rotary has a new President - St. Lucia Voice News". Archived from the original on 22 December 2015.
  39. "Another service station sues SOL over fuel volume discrepancy". iWitness News.
  40. "New Measures to Improve TCI Finances And Prioritise Spending". TheBahamasWeekly.com.
  41. E. Frank Henriques, The Signet Encyclopedia of Wine, p. 298
  42. Cherry, Rona (11 October 1976). "Liquor Industry Converts to Metric System". The New York Times.
  43. "gallon, n.". Oxford English Dictionary (2 ed.). Oxford, England: Oxford University Press. 1989.
  44. "English wine gallon". Sizes.com. Retrieved 17 June 2010.
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