Troy weight

{{Short description|System of units of mass}} [[File:Gold1oz.jpg|thumb|''Troy ounce'' is a traditional unit of gold {{snd}}‌this sample marked "999,9" is {{em|four nines fine}} {{xref|(see: {{slink|Fineness|Gold}})}}, meaning it is pure to 999.9 parts in 1,000 (''i.e.''{{px2}}99.99% pure)]] [[File:Ingots of Ge, Fe, Al, Re, Os, one troy ounce each (2).jpg|thumb|{{convert|1|ozt|gr g|spell=In|adj=off|abbr=off}} samples of germanium, iron, aluminium, rhenium and osmium. The differences in size are due to differences in density.]] [[File:1000oz.silver.bullion.bar.underneath.png|thumb|A Good Delivery silver bar weighing 1,000 troy ounces (about 83 troy pounds or 31 kg)]]

'''Troy weight''' is a system of units of mass whose origin is uncertain.<ref name="HallockWade1906">{{Cite book |last1=Hallock |first1=William |author-link1=William Hallock |last2=Wade |first2=Herbert Treadwell |year=1906 |title=Outlines of the Evolution of Weights and Measures and the Metric System |url=https://archive.org/details/outlinesevoluti00hallgoog |location=New York and London |publisher=The Macmillan Company |page=[https://archive.org/details/outlinesevoluti00hallgoog/page/n57/mode/1up 33] |access-date=14 August 2012}}</ref> By far the most common troy unit is the troy ounce (oz t), the standard mass unit for precious metals in industry and in trade; it equals 31.1034768 grams.<ref name="Perth Mint" /> The troy weight units are the grain, the pennyweight (24 grains), the troy ounce (20 pennyweights), and the troy pound (12 troy ounces). The troy grain is equal to the grain unit of the avoirdupois and apothecaries' systems, but the troy ounce is heavier than the avoirdupois ounce, and the troy pound is lighter than the avoirdupois pound.

==Etymology== Troy weight is generally supposed to take its name from the French market town of Troyes where English merchants traded at least as early as the early 9th century.<ref name="OED3troy2">{{cite book|title=Oxford English Dictionary|chapter-url=http://www.oed.com/view/Entry/206831|date=June 2012|publisher=Oxford University Press|location=Oxford, England|chapter=troy, n.2|quote=The received opinion is that it took its name from a weight used at the fair of Troyes in France|title-link=Oxford English Dictionary}}</ref><ref>{{cite book|last=Partridge|first=Eric|author-link=Eric Partridge|title=Origins: A Short Etymological Dictionary of Modern English|chapter-url=https://archive.org/details/originsshortetym0000part_z7h8|chapter-url-access=registration|year=1958|publisher=Routledge and Kegan Paul|location=London|page=3566|chapter=Trojan|oclc=250202885|quote=...the great fairs established for all Europe the weight-standard ''Troyes'', whence...''Troy''...}}</ref> The name ''troy'' is first attested in 1390, describing the weight of a platter, in an account of the travels in Europe of the Earl of Derby.<ref name="OED3troy2" /><ref>{{cite book|last=Smith|first=L. Toulmin|author-link=Lucy Toulmin Smith|title=Expeditions to Prussia and the Holy Land Made by Henry Earl of Derby (afterwards King Henry IV.) in the Years 1390-1 and 1392-3|url=https://archive.org/details/expeditionstopr00smitgoog|page=[https://archive.org/details/expeditionstopr00smitgoog/page/n220 100]|year=1894|publisher=Camden Society|location=London}}</ref>

Charles Moore Watson (1844–1916) proposes an alternative etymology: ''The Assize of Weights and Measures'' (also known as {{lang|la|Tractatus de Ponderibus et Mensuris}}), one of the statutes of uncertain date from the reign of either Henry III or Edward I, thus before 1307, specifies "{{lang|la|troni ponderacionem}}"—which the Public Record Commissioners translate as "troy weight". The word {{lang|la|tron}} refers to markets.{{citation-needed|date=March 2024}} Wright's ''The English Dialect Dictionary'' lists the word ''troi'' as meaning a balance, related to the alternate form 'tron' which also means market or the place of weighing. From this, Watson suggests that 'troy' derives from the manner of weighing by balance precious goods such as bullion or drugs; in contrast to the word 'avoirdupois' used to describe bulk goods such as corn or coal, sometimes weighed in ancient times by a kind of steelyard called the auncel.<ref name="CMW1910"/>

Troy weight referred to the Tower system; the earliest reference to the modern troy weights is in 1414.<ref name="CMW1910">{{cite book |last=Watson |first=Charles Moore |url=https://archive.org/stream/britishweightsme00watsuoft/ |title=British weights and measures as described in the laws of England from Anglo-Saxon times |publisher=John Murray |year=1910 |location=London |page= |pages=32-33 |oclc=4566577}}</ref><ref>{{cite book|last=Wright|first=Joseph|author-link=Joseph Wright (linguist)|title=The English Dialect Dictionary|volume=6|year=1898|publisher=English Dialect Society|location=Oxford|page=250|oclc=63381077}}</ref>

==History== The origin of the troy weight system is unknown, although the name probably comes from the Champagne fairs at Troyes, in northeastern France.<ref>{{cite book |last=Smith |first=Adam |url=https://books.google.com/books?id=PeJMAAAAIAAJ&pg=PA35 |title=An Inquiry Into the Nature and Causes of the Wealth of Nations |date=1809 |publisher=T. Hamilton |volume=1 |location=London |page=35 |quote=The French livre contained, in the time of Charlemagne, a pound, Troyes weight, of silver of a known finess. The fair of Troyes in Champaign was at that time frequented by all the nations of Europe, and the weights and measures of so famous a market were generally known and esteemed.}}</ref> English troy weights were nearly identical to the troy weight system of Bremen. (The Bremen troy ounce had a mass of 480.8 British Imperial grains.)<ref name="1977zupko" />

Many aspects of the troy weight system were indirectly derived from the Roman monetary system. Before they used coins, early Romans used bronze bars of varying weights as currency. An {{Lang|la|aes grave}} ("heavy bronze") weighed one pound. One twelfth of an {{lang|la|aes grave}} was called an {{lang|la|uncia}}, or in English, an "ounce". Before the adoption of the metric system, many systems of troy weights were in use in various parts of Europe, among them Holland troy, Paris troy, etc.<ref name="Kelly"/> Their values varied from one another by up to several percentage points. Troy weights were first used in England in the 15th century and were made official for gold and silver in 1527.<ref name="HallockWade1906" /> The British Imperial system of weights and measures (also known as imperial units) was established in 1824, prior to which the troy weight system was a subset of pre-imperial English units.

The troy ounce in modern use is essentially the same as the British Imperial troy ounce (1824–1971), adopted as an official weight standard for United States coinage by act of Congress on May 19, 1828.<ref>{{cite book | last = Hallock, Wade | title = Outlines of the evolution of weights and measures and the metric system | url = https://archive.org/details/outlinesevoluti00wadegoog | publisher=The Macmillan company | year = 1906 | page = [https://archive.org/details/outlinesevoluti00wadegoog/page/n134 119] }}</ref> The British Imperial troy ounce (known more commonly simply as the imperial troy ounce) was based on, and virtually identical to, the pre-1824 British troy ounce and the pre-1707 English troy ounce. (1824 was the year the British Imperial system of weights and measures was adopted; 1707 was the year of the Act of Union which created the Kingdom of Great Britain.) Troy ounces have been used in England since the early 15th century, and the English troy ounce was officially adopted for coinage in 1527. Before that time, various sorts of troy ounces were in use on the continent.<ref name="1977zupko">{{cite book | last = Zupko | first = Ronald Edward | author-link = Ronald Edward Zupko | title = British Weights and Measures: A History from Antiquity to the Seventeenth Century | publisher=University of Wisconsin Press | year = 1977 | isbn = 978-0-299-07340-4 | pages = 28–9 }}</ref>

The troy ounce and grain were also part of the apothecaries' system. This was long used in medicine, but has been largely replaced by the metric system (milligrams).<ref name="dictionary.com">{{cite web | title=Troy Ounce | url=http://dictionary.reference.com/browse/troy%20ounce | work=WordNet 3.0, Dictionary.com | publisher=Princeton University | access-date=2008-01-10 | url-status=live | archive-url=https://web.archive.org/web/20080226004653/http://dictionary.reference.com/browse/troy%20ounce | archive-date=2008-02-26 }}</ref> The only troy weight in widespread use is the British Imperial troy ounce and its American counterpart. Both are based on a grain of 0.06479891 gram (exact, by definition), with 480 grains to a troy ounce (compared with {{frac|437|1|2}} grains for an ounce avoirdupois). The British Empire abolished the 12-ounce troy pound in the 19th century. It has been retained, though rarely used, in the American system. Larger amounts of precious metals are conventionally counted in hundreds or thousands of troy ounces, or in kilograms.

Troy ounces have been and are still often used in precious metal markets in countries that otherwise use International System of Units (SI).<ref>{{cite web|url=http://www.boerse-frankfurt.de/de/rohstoffe/xetra+gold|title=Börse Frankfurt: Aktien, Kurse, Charts und Nachrichten|website=www.boerse-frankfurt.de|access-date=28 April 2018|url-status=live|archive-url=https://web.archive.org/web/20151101044103/http://www.boerse-frankfurt.de/de/rohstoffe/xetra+gold|archive-date=1 November 2015}}</ref><ref>{{cite web|url=http://www.perthmint.com.au/education_uom.aspx|title=Units of Measure - The Perth Mint|url-status=live|archive-url=https://web.archive.org/web/20150924071802/http://www.perthmint.com.au/education_uom.aspx |archive-date=2015-09-24}}</ref> However, the People's Bank of China{{snd}} which had been using troy measurements in minting Gold Pandas since 1982{{snd}} from 2016 specifies Chinese bullion coins in an integer numbers of grams.<ref>{{cite web |url=http://www.numismaster.com/ta/numis/Article.jsp?ArticleId=28158 |title=Do grams or ounces win? |url-status=dead |archive-url=https://web.archive.org/web/20160506234211/http://www.numismaster.com/ta/numis/Article.jsp?ArticleId=28158|archive-date=2016-05-06 |first= Pat |last=Heller |date=December 21, 2015 |website=Numismaster.com}}</ref>

==Units of measurement== thumb|Chart comparing the mass (in grams) of tower, Troy, merchant, avoirdupois and London pounds. Each colored block represents one of that system's ounces (gold=Troy, blue= avoirdupois, purple=tower)

===Troy pound (lb t) === [[File:TroyPoundEngraving.jpg|thumb|The standard British troy pound manufactured in 1758; it bears the abbreviation {{char|℔}} ("pound") and the letter "T" for troy.]] The troy pound (lb t) consists of twelve troy ounces<ref name="Perth Mint">{{cite web |title=Units of measure | publisher=Perth Mint |url=https://www.perthmint.com/education_uom.aspx |url-status=dead |archive-url=https://web.archive.org/web/20190607051942/https://www.perthmint.com/education_uom.aspx |archive-date=7 June 2019}}</ref> and thus is {{convert|5760|gr|g|abbr=off|sigfig=8|comma=gaps}}. (An avoirdupois pound is approximately 21.53% heavier, at {{convert|7000|gr|g|abbr=off|sigfig=8|comma=gaps}}, and consists of sixteen avoirdupois ounces.)

===Troy ounce (oz t) === A troy ounce is 480 grains.<ref name="Perth Mint" /> Since the implementation of the international yard and pound agreement of 1 July 1959, the grain measure is precisely {{val|64.79891|u=milligrams}}.<ref name="NIST">{{cite report |publisher=National Institute of Standards and Technology |date=October 2011 |editor-last1= Butcher |editor-first1=Tina |editor-last2=Cook |editor-first2=Steve |editor-last3=Crown |editor-first3=Linda |url=https://www.nist.gov/pml/wmd/pubs/upload/AppC-12-hb44-final.pdf |title="Appendix C – General Tables of Units of Measurement" |archive-url=https://web.archive.org/web/20160617040949/http://www.nist.gov/pml/wmd/pubs/upload/AppC-12-hb44-final.pdf |archive-date=2016-06-17 }} in {{cite report |url=https://www.nist.gov/pml/wmd/pubs/h44-12.cfm |title=Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices |archive-url=https://web.archive.org/web/20160823052024/http://www.nist.gov/pml/wmd/pubs/h44-12.cfm |archive-date=2016-08-23 }}</ref> <ref>{{cite book |title=NIST Handbook |volume=44| edition=2012 |location=Washington, D.C.: U.S. |publisher=Department of Commerce, Technology Administration, National Institute of Standards and Technology.| issn=0271-4027 |url=https://www.worldcat.org/search?q=n2:0271-4027 |archive-url=https://web.archive.org/web/20221225104227/https://www.worldcat.org/search?q=n2:0271-4027 |archive-date=2022-12-25 | oclc=58927093}}</ref>{{rp|C-19}}<ref name="nbs447">{{cite book |last=Judson |first=Lewis V. |title=Weights and Measures Standards of the United States: A brief history |url=https://www.nist.gov/pml/pubs/sp447/index.cfm |format=PDF |access-date=30 June 2012 |series=NBS Special Publication |volume=447 |date=March 1976 |orig-year=October 1963 |publisher=U.S. Department of Commerce, National Bureau of Standards |location=Washington, D.C. |oclc=610190761 |page=20 |chapter=8. Refinement of values for the yard and pound |chapter-url=http://physics.nist.gov/Pubs/SP447/sec08.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110603064530/https://www.nist.gov/pml/pubs/sp447/index.cfm |archive-date=3 June 2011 }}</ref> Thus one troy ounce = {{convert|1|ozt|gr|0|disp=out|abbr=off|comma=gaps}} × {{convert|1|gr|g|8|disp=out|abbr=off|comma=gaps}}/grain = {{convert|1|ozt|g|8|disp=out|abbr=off|comma=gaps}}. Since the ounce avoirdupois is 437.5 grains, a troy ounce is exactly {{frac|480|437.5}} = {{frac|192|175}} or about 1.09714 ounces avoirdupois or about 9.7% more. The troy ounce for trading precious metals is considered to be sufficiently approximated by 31.10 g in EU directive 80/181/EEC.<ref name="80/181/EER">{{cite web | url=https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:01980L0181-20200613#tocId31 | title=Consolidated TEXT: 31980L0181 — EN — 13.06.2020 }}</ref> The troy ounce is the only troy unit allowed in trade in the United Kingdom, and only for precious metals, since the implementation of the Weights and Measures Act of 1985.<ref>{{Cite web |others= |title=Weights and Measures Act 1985 |url=https://www.legislation.gov.uk/ukpga/1985/72/section/8#:~:text=(a)-,the%20ounce%20troy,-%2C%20except%20for%20the |archive-url= |archive-date= |access-date=2025-07-27 |website=www.legislation.gov.uk |at=UK Public General Acts > 1985 c. 72 > Part II > General > Section 8 > Subsection (2)(a) |language=en}}</ref>

The Dutch troy system is based on a {{Lang|nl|mark}} of 8 Dutch ounces, the ounce of 20 {{Lang|nl|engels}} (pennyweights), the {{Lang|nl|engel}} of 32 {{Lang|nl|azen}}. The {{Lang|nl|mark}} was rated as 3,798 troy grains or 246.084 grams. The divisions are identical to the tower system.<ref name="Kelly">{{cite book |last=Kelly |first=Patrick|title=Universal Cambist and Commercial Instructor |url=https://archive.org/details/universalcambist0001kell/page/n6/mode/1up |year=1821 |location=London |page=[https://archive.org/details/universalcambist0001kell/page/20/mode/1up 20]}}</ref>

===Pennyweight (dwt)=== The pennyweight symbol is ''dwt''. One pennyweight is 24 grains, and 20 pennyweights make one troy ounce.<ref name="Perth Mint" /> Because there are 12 troy ounces in the old troy pound, there are 240 pennyweights to the pound (mass){{snd}} just as there are 240 pennies in the original pound-sterling. However, prior to 1526, the English pound sterling was based on the tower pound, which is {{frac|15|16}} of a troy pound. The ''d'' in ''dwt'' stands for ''denarius'', the ancient Roman coin that equates loosely to a penny. The symbol ''d'' for penny can be recognized in the form of British pre-decimal pennies, in which pounds, shillings, and pence are indicated using the symbols ''£'', ''s'', and ''d'', respectively.

===Troy grain=== {{main|Grain (mass)}}

There is no specific 'troy grain'. All Imperial systems use the same measure of mass called a grain (historically of barley), each weighing {{frac|1|7000}} of an avoirdupois pound (and thus a little under 65 milligrams).{{Efn|Because an avoirdupois pound is 7000 grains and a pound is legally defined as having a mass of exactly 0.45359237{{nbsp}}kg (453.59237 g, 453592.37 mg), one grain is 453592.37/7000{{nbsp}}mg or 64.79891{{nbsp}}mg.}}

===Mint masses=== Mint masses, also known as ''moneyers' masses'', were legalized by Act of Parliament dated 17 July 1649 entitled ''An Act touching the monies and coins of England''. A grain is 20 mites, a mite is 24 droits, a droit is 20 perits, a perit is 24 blanks.<ref name="Britain)1891">{{cite book|publisher=Philological Society (Great Britain)|title=A new English dictionary on historical principles: founded mainly on the materials collected by the Philological Society|url=https://books.google.com/books?id=k2xXAAAAYAAJ&pg=PA675|year=1891|via=Clarendon Press|page=675}}</ref><ref name="Miege">{{cite book|last=Miege|first= Guy|title=The Present State of Great Britain and Ireland|url=https://books.google.com/books?id=BDs2AAAAMAAJ&pg=PA307|year=1738|publisher=J. Brotherton, A. Bettesworth and C. Hitch, G. Strahan, W. Mears, R. Ware, E. Symon, and J. Clark|page=307}}</ref>

==Conversions== {| class="wikitable" ! Unit !! Grains !! Grams (exact) |- | Troy pound (12 troy ounces) || style="text-align:right;"| 5,760 || style="text-align:right;"| 373.24172 160 |- | Troy ounce (20 pennyweights) || style="text-align:right;"| 480 || style="text-align:right;"| 31.10347 680 |- | Pennyweight || style="text-align:right;"| 24 || style="text-align:right;"| 1.55517 384 |- | Grain || style="text-align:right;"| 1 || style="text-align:right;"| 0.06479 891 |}

The troy system was used in the apothecaries' system but with different further subdivisions.

==See also== * Bullion coin * Carat (mass) * Conversion of units * Fluid ounce * Mark (unit) * Tola (unit), a traditional unit of mass equal to exactly {{frac|3|8}} of a troy ounce * United States customary units

== Explanatory footnotes == {{Notelist}}

==References== {{Reflist}}

Category:Precious metals Category:Units of mass Category:Customary units of measurement in the United States Category:Systems of units