Editing Imperial units (section)

=== Mass and weight ===
In the 19th and 20th centuries, the UK used three different systems for mass and weight.

* [[troy weight]], used for precious metals;
* [[avoirdupois]] weight, used for most other purposes; and
* [[apothecaries' weight]], now virtually unused since the metric system is used for all scientific purposes.

The distinction between [[mass versus weight|mass and weight]] is not always clearly drawn. Strictly a pound is a unit of mass, but it is commonly referred to as a weight. When a distinction is necessary, the term ''[[pound-force]]'' may refer to a unit of force rather than mass. The troy pound ({{val|373.2417216|u=g}}) was made the primary unit of mass by the [[Weights and Measures Act 1824]] and its use was abolished in the UK on 1 January 1879,<ref name="Britain1878">{{cite book|author=Great Britain|title=Statutes at large ...|url=https://books.google.com/books?id=v39KAAAAMAAJ&pg=PA308|year=1878|page=308}}</ref> with only the troy ounce ({{val|31.1034768|u=g}}) and its [[decimal]] subdivisions retained.<ref name="Chisholm1911">{{Cite EB1911 |wstitle= Weights and Measures |volume= 28 |pages= 477&ndash;494; see page 480 |first= Henry James |last= Chaney }}</ref> The [[Weights and Measures Act 1855]] made the avoirdupois pound the primary unit of mass.<ref name="Britain1855">{{cite book|author=Great Britain|title=A collection of public general statutes passed in the 18th and 19th years of the reign of Her Majesty Queen Victoria|url=https://books.google.com/books?id=L1YMAQAAMAAJ&pg=PA273|year=1855|pages=273–75}}</ref> In all the systems, the fundamental unit is the [[Pound (mass)|pound]], and all other units are defined as fractions or multiples of it.

{| class="wikitable" style="margin-right:0"
|+ Table of mass units
! Unit
! Pounds
! In SI units
! Notes
|-
|align=center| [[Grain (mass)|grain]] (gr)
|align=right| {{frac|{{val|7000}}}}
|align=right| {{val|64.79891|u=mg}}
|Exactly {{val|64.79891}} milligrams.
|-
|align=center| [[Dram (unit)|drachm]] (dr)
|align=right| {{frac|256}}
|align=right| {{val|1.7718451953125|u=g}}
| A dram is {{frac|16}} of an ounce
|-
|align=center| [[ounce]] (oz)
|align=right| {{frac|16}}
|align=right| {{val|28.349523125|u=g}}
| An ounce is {{frac|16}} of a pound
|-
|align=center| [[Pound (mass)|pound]] (lb)
|align=right| 1
|align=right| {{val|0.45359237|u=kg}}
|Defined by the [[Units of Measurement Regulations 1994]] ([[SI 1994]]/2867)<ref>{{Cite web|url=http://www.legislation.gov.uk/uksi/1994/2867/schedule/made|title=The Units of Measurement Regulations 1994|website=legislation.gov.uk|language=en|access-date=2019-03-13|archive-date=25 February 2021|archive-url=https://web.archive.org/web/20210225025135/https://www.legislation.gov.uk/uksi/1994/2867/schedule/made|url-status=live}}</ref>
|-
|align=center| [[Stone (Imperial mass)|stone]] (st)
|align=right| 14
|align=right| {{val|6.35029318|u=kg}}
|The plural ''stone'' is often used when providing a weight (e.g. "this sack weighs 8 stone").<ref name=":0">{{Cite web|title = Definition of stone in English from the Oxford dictionary|url = http://www.oxforddictionaries.com/definition/english/stone|archive-url = https://web.archive.org/web/20120711200915/http://oxforddictionaries.com/definition/english/stone|url-status = dead|archive-date = 11 July 2012|website = www.oxforddictionaries.com|publisher = Oxford University Press|access-date = 2015-11-25|ref = stonedefinition}}</ref> A person's weight is usually quoted in stone and pounds in English-speaking countries that use the avoirdupois system, with the exception of the United States and Canada, where it is usually quoted in pounds.
|-
|align=center| [[quarter (unit)|quarter]] (qr or qtr)
|align=right| 28
|align=right| {{val|12.70058636|u=kg}}
|{{anchor|qtr}} One quarter (literally a quarter of a hundredweight) is equal to two stone or 28 pounds. The term ''quarter'' is also used in retail contexts, where it refers to four ounces, i.e. a quarter of a pound. (The 1824 act defined a quarter as a unit of volume, as above: thus a 'quarter of wheat', 64 gallons, would weigh about 494 lb.<ref>{{cite web | url= https://www.engineeringtoolbox.com/foods-materials-bulk-density-d_1819.html | title= Bulk densities of some common food products | website= engineeringtoolbox.com | access-date= 19 January 2020 | archive-date= 5 July 2020 | archive-url= https://web.archive.org/web/20200705195715/https://www.engineeringtoolbox.com/foods-materials-bulk-density-d_1819.html | url-status= live }} The density of wheat is 0.770, and 291*0.770={{convert|224|kg}}.</ref>).
|-
|align=center| [[hundredweight]] (cwt)
|align=right| 112
|align=right| {{val|50.80234544|u=kg}}
|One imperial hundredweight is equal to eight stone. This is the ''long hundredweight'', 112 pounds, as opposed to the short hundredweight of 100 pounds used in the United States and Canada.<ref name="justice1">''[http://laws-lois.justice.gc.ca/eng/acts/W-6/page-15.html/ Weights and Measures Act] {{Webarchive|url=https://web.archive.org/web/20121016084035/http://laws-lois.justice.gc.ca/eng/acts/W-6/page-15.html/ |date=16 October 2012 }}''</ref>
|-
|align=center| [[long ton|ton]] (t{{Citation needed|date=November 2023|reason=Usually "t" stands for "metric ton" (or "tonne"); the article for [[Long ton]] states that its abbreviation is "LT" (but also lacks citation)}})
|align=right| 2240
|align=right| {{val|1016.0469088|u=kg}}
|Twenty hundredweight equals a ton (as in the US and Canadian<ref name="justice1"/> systems). The imperial hundredweight is 12% greater than the US and Canadian one. The imperial ton (or ''long ton'') is {{val|2240}} pounds, which is much closer to a [[tonne]] (about {{val|2204.6}} pounds), compared to the 10.7% smaller North American ''short ton'' of {{convert|2000|lb|kg|3|comma=gaps}}.
|-
| style="text-align:center;" colspan="6"| '''Gravitational units'''
|- valign=top
|align=center| [[slug (unit)|slug]] (slug)
|align=right| {{val|32.17404856}}
|align=right| {{val|14.59390294|u=kg}}
|The slug, a unit associated with imperial and US customary systems, is a mass that accelerates by 1&nbsp;ft/s<sup>2</sup> when a force of one [[pound (force)|pound]] (lbf) is exerted on it.<ref>{{cite web|url=http://www.wolframalpha.com/input/?i=Slug&a=*C.Slug-_*Unit-|title=Wolfram-Alpha: Computational Knowledge Engine|access-date=23 June 2015|archive-date=14 January 2023|archive-url=https://web.archive.org/web/20230114132639/https://www.wolframalpha.com/input/?i=Slug&a=%2AC.Slug-_%2AUnit-|url-status=live}}</ref>
::{|
|-
|  ||align=right| ''F''&nbsp;||= ''ma'' ([[Newton's second law]])
|-
|  ||align=right| 1 lbf&nbsp;||= 1 slug × 1&nbsp;ft/s<sup>2</sup> (as defined above)
|-
|  ||align=right| 1 lbf&nbsp;||= 1 lb × [[standard gravity|''g'']]/gc (by definition of the pound force{{citation needed|date=October 2017}})
|-
|  ||align=right| ''g''&nbsp;||≈ {{val|32.17404856}}&nbsp;ft/s<sup>2</sup>
|-
|  ||align=right| ''gc''&nbsp;||≈ {{val|32.17404856}}&nbsp;lbm⋅ft/lbf⋅s<sup>2</sup>
|-
|∴ ||align=right| 1 slug&nbsp;||≈ {{val|32.17404856}}&nbsp;pounds
|}
|}