Troy weight

Last updated
Troy ounce is a traditional unit of gold weight. 1 oz of fine gold.jpg
Troy ounce is a traditional unit of gold weight.
One-troy-ounce (480 gr; 31 g) samples of germanium, iron, aluminium, rhenium and osmium Ingots of Ge, Fe, Al, Re, Os, one troy ounce each (2).jpg
One-troy-ounce (480 gr; 31 g) samples of germanium, iron, aluminium, rhenium and osmium
A Good Delivery silver bar weighing 1,000 troy ounces (83 troy pounds; 31 kg)
A Good Delivery silver bar weighing 1,000 troy ounces (83 troy pounds; 31 kg)

Troy weight is a system of units of mass that originated in 15th-century Kingdom of England [1] and is primarily used in the precious metals industry. 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 system, but the troy ounce is heavier than the avoirdupois ounce, and the troy pound is lighter than the avoirdupois pound. One troy ounce (oz t) equals exactly 31.1034768 grams.



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. [2] [3] 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. [2] [4]

Charles Moore Watson (1844–1916) proposes an alternative etymology: The Assize of Weights and Measures (also known as 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 "troni ponderacionem"—which the Public Record Commissioners translate as "troy weight". The word troni refers to markets.[ citation needed ] 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. [5]

Troy weight referred to the Tower system; the earliest reference to the modern troy weights is in 1414. [5] [6]


The origin of the troy weight system is unknown. Although the name probably comes from the Champagne fairs at Troyes, in northeastern France. [7] 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.) [8]

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 aes grave ("heavy bronze") weighed one pound. One twelfth of an aes grave was called an 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. [9] 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. [1] 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. [10] The British Imperial troy ounce (known more commonly simply as the imperial troy ounce) was based on, and virtually identical with, 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. [8]

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). [11] 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 437+12 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), [12] [13] except in East Asia. [14] However, the People's Bank of China has previously used troy measurements in minting Gold Pandas beginning in 1982; since 2016, the use of troy ounces has been replaced by integer numbers of grams.

Units of measurement

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) Comparison of pounds.svg
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)

The standard British troy pound manufactured in 1758; it bears the abbreviation  ("pound") and the letter "T" for troy. TroyPoundEngraving.jpg
The standard British troy pound manufactured in 1758; it bears the abbreviation ("pound") and the letter "T" for troy.

The troy pound (lb t) consists of twelve troy ounces [15] and thus is 5760 grains (373.24172 grams). (An avoirdupois pound is approximately 21.53% heavier at 7000 grains, and consists of sixteen avoirdupois ounces).

Troy ounce (oz t)

A troy ounce weighs 480 grains. [15] Since the implementation of the international yard and pound agreement of 1 July 1959, the grain measure is defined as precisely 64.79891  milligrams . [16] :C-19 [17] Thus one troy ounce = 480 grains × 0.06479891 grams/grain = 31.10347680 grams. Since the ounce avoirdupois is defined as 437.5 grains, a troy ounce is exactly 480437.5 = 192175 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 [18]

The Dutch troy system is based on a mark of 8 ounces, the ounce of 20 engels (pennyweights), the Engel of 32 as. The mark was rated as 3,798 troy grains or 246.084 grammes. The divisions are identical to the tower system. [19]

Pennyweight (dwt)

The pennyweight symbol is dwt. One pennyweight weighs 24 grains, and 20 pennyweights make one troy ounce. [15] Because there were 12 troy ounces in the old troy pound, there would have been 240 pennyweights to the pound (mass)  just as there were 240 pennies in the original pound-sterling. However, prior to 1526, the English pound sterling was based on the tower pound, which is 1516 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 were indicated using the symbols £, s, and d, respectively.

Troy grain

There is no specific 'troy grain'. All Imperial systems use the same measure of mass called a grain (historically of barley), weighing exactly 64.79891 milligrams. [lower-alpha 1]

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. [20] [21]


UnitGrainsGrams (exact)
Troy pound (12 troy ounces)5,760373.24172 16
Troy ounce (20 pennyweights)48031.10347 68
Pennyweight241.55517 384
Grain10.06479 891
English pounds
Unit PoundsOuncesGrainsMetric
Avoirdupois1175/144= 1.2152735/27= 1.29628/27= 1.03735/36= 0.972≈ 0.90721614+7/12= 14.58315+5/9= 15.57,00009,955+5/9≈ 4545/11
Troy144/175≈ 0.8229116/15= 1.0664/75= 0.8534/5= 0.8≈ 0.746513+29/175≈ 13.171212+4/5= 12.85,76008,192≈ 3733/8
Tower27/35≈ 0.771415/16= 0.937514/5= 0.83/4= 0.75≈ 0.699812+12/35≈ 12.3411+1/4= 11.25125,40007,680≈ 3507/20
Merchant27/28≈ 0.964375/64= 1.1718755/4= 1.25115/16= 0.9375≈ 0.874815+3/7≈ 15.4314+1/16= 14.0625156,75009,600≈ 4377/16
London36/35≈ 1.0295/4= 1.254/3= 1.316/15= 1.061≈ 0.933116+16/35≈ 16.4615167,20010,240≈ 4677/15
Metric≈ 1.1023≈ 1.3396≈ 1.4289≈ 1.1431≈ 1.07171≈ 17.64≈ 16.08≈ 17.157,71610,974= 500= 1/2

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

See also


  1. Because an avoirdupois pound weighs 7000 grains and a pound weighs exactly 0.45359237 kg (see International Yard and Pound Agreement). Thus one grain weighs 453.59237/7 mg.

Related Research Articles

<span class="mw-page-title-main">Carat (mass)</span> Unit of mass

The carat (ct) is a unit of mass equal to 200 mg, which is used for measuring gemstones and pearls. The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world. The carat is divisible into 100 points of 2 mg. Other subdivisions, and slightly different mass values, have been used in the past in different locations.

<span class="mw-page-title-main">Imperial units</span> System of measurements

The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.

<span class="mw-page-title-main">Pound (mass)</span> Unit of mass

The pound or pound-mass is a unit of mass used in both the British imperial and United States customary systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm, #, and or ″̶.

<span class="mw-page-title-main">United States customary units</span> System of units of measurement commonly used in the United States

United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are noticeable differences between the systems.

<span class="mw-page-title-main">Gram</span> Metric unit of mass

The gram is a unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.

<span class="mw-page-title-main">Grain (unit)</span> Unit of mass

A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and apothecaries' systems, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single ideal seed of a cereal. From the Bronze Age into the Renaissance, the average masses of wheat and barley grains were part of the legal definitions of units of mass. Expressions such as "thirty-two grains of wheat, taken from the middle of the ear" appear to have been ritualistic formulas. Another source states that it was defined such that 252.458 units would balance 1 cubic inch (16 cm3) of distilled water at an ambient air-water pressure and temperature of 30 inches of mercury (100 kPa) and 62 °F (17 °C) respectively. Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally.

The ounce is any of several different units of mass, weight, or volume and is derived almost unchanged from the uncia, an Ancient Roman unit of measurement.

<span class="mw-page-title-main">Avoirdupois</span> System of weights based on a pound of 16 ounces

Avoirdupois is a measurement system of weights that uses pounds and ounces as units. It was first commonly used in the 13th century AD and was updated in 1959.

<span class="mw-page-title-main">Pennyweight</span> Unit of mass

A pennyweight (dwt) is a unit of mass equal to 24 grains, 120 of a troy ounce, 1240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams. It is abbreviated dwt, d standing for denarius –, and later used as the symbol of an old British penny.

<span class="mw-page-title-main">Bushel</span> Unit of volume with numerous different definitions

A bushel 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 agricultural products, such as wheat. In modern usage, the volume is nominal, with bushels denoting a mass defined differently for each commodity.

The dram is a unit of mass in the avoirdupois system, and both a unit of mass and a unit of volume in the apothecaries' system. It was originally both a coin and a weight in ancient Greece. The unit of volume is more correctly called a fluid dram, fluid drachm, fluidram or fluidrachm.

<span class="mw-page-title-main">Apothecaries' system</span> Historical system of mass and volume units used by physicians and apothecaries

The apothecaries' system, or apothecaries' weights and measures, is a historical system of mass and volume units that were used by physicians and apothecaries for medical prescriptions and also sometimes by scientists. The English version of the system is closely related to the English troy system of weights, the pound and grain being exactly the same in both. It divides a pound into 12 ounces, an ounce into 8 drachms, and a drachm into 3 scruples of 20 grains each. This exact form of the system was used in the United Kingdom; in some of its former colonies, it survived well into the 20th century. The apothecaries' system of measures is a similar system of volume units based on the fluid ounce. For a long time, medical recipes were written in Latin, often using special symbols to denote weights and measures.

A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or SI, the British imperial system, and the United States customary system.

English units were the units of measurement used in England up to 1826, which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.

<span class="mw-page-title-main">History of measurement</span>

The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.

<span class="mw-page-title-main">Comparison of the imperial and US customary measurement systems</span>

Both the British imperial measurement system and United States customary systems of measurement derive from earlier English unit systems used prior to 1824 that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units.

<span class="mw-page-title-main">Weights and Measures Acts (UK)</span> Laws of the British Parliament determining the regulation of weights and measures

Weights and measures acts are acts of the British Parliament determining the regulation of weights and measures. It also refers to similar royal and parliamentary acts of the Kingdoms of England and Scotland and the medieval Welsh states. The earliest of these were originally untitled but were given descriptive glosses or titles based upon the monarch under whose reign they were promulgated. Several omnibus modern acts are entitled the Weights and Measures Act and are distinguished by the year of their enactment.

<span class="mw-page-title-main">Imperial and US customary measurement systems</span> English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.

The quarter was used as the name of several distinct English units based on ¼ sizes of some base unit.

The Exchequer Standards may refer to the set of official English standards for weights and measures created by Queen Elizabeth I, and in effect from 1588 to 1825, when the Imperial units system took effect, or to the whole range of English unit standards maintained by the Court of the Exchequer from the 1200s, or to the physical reference standards physically kept at the Exchequer and used as the legal reference until the such responsibility was transferred in the 1860s, after the Imperial system had been established.


  1. 1 2 Hallock, William; Wade, Herbert Treadwell (1906). Outlines of the Evolution of Weights and Measures and the Metric System. New York and London: The Macmillan Company. p.  34 . Retrieved 14 August 2012.
  2. 1 2 "troy, n.2". Oxford English Dictionary. Oxford, England: Oxford University Press. June 2012. The received opinion is that it took its name from a weight used at the fair of Troyes in France
  3. Partridge, Eric (1958). "Trojan" . Origins: A Short Etymological Dictionary of Modern English. London: Routledge and Kegan Paul. p. 3566. OCLC   250202885. …the great fairs established for all Europe the weight-standard Troyes, whence…Troy
  4. Smith, L. Toulmin (1894). 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. London: Camden Society. p.  100.
  5. 1 2 Watson, Charles Moore (1910). British weights and measures as described in the laws of England from Anglo-Saxon times. London: John Murray. p. 82. OCLC   4566577.
  6. Wright, Joseph (1898). The English Dialect Dictionary. Vol. 6. Oxford: English Dialect Society. p. 250. OCLC   63381077.
  7. Smith, Adam (1809). An Inquiry Into the Nature and Causes of the Wealth of Nations. Vol. 1. London: T. Hamilton. p. 35. 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.
  8. 1 2 Zupko, Ronald Edward (1977). British Weights and Measures: A History from Antiquity to the Seventeenth Century. University of Wisconsin Press. pp. 28–9. ISBN   978-0-299-07340-4.
  9. Kelly, Patrick (1811). The Universal Cambist and Commercial Instructor. Vol. 1. p. 20.
  10. Hallock, Wade (1906). Outlines of the evolution of weights and measures and the metric system. The Macmillan company. p.  119.
  11. "Troy Ounce". WordNet 3.0, Princeton University. Archived from the original on 2008-02-26. Retrieved 2008-01-10.
  12. "Börse Frankfurt: Aktien, Kurse, Charts und Nachrichten". Archived from the original on 1 November 2015. Retrieved 28 April 2018.
  13. "Units of Measure - The Perth Mint". Archived from the original on 2015-09-24.
  14. "Do grams or ounces win?". Archived from the original on 2016-05-06.
  15. 1 2 3 "Units of measure". Perth Mint. Archived from the original on 7 June 2019.
  16. National Institute of Standards and Technology (October 2011). Butcher, Tina; Cook, Steve; Crown, Linda et al. eds. "Appendix C – General Tables of Units of Measurement" Archived 2016-06-17 at the Wayback Machine (PDF). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices Archived 2016-08-23 at the Wayback Machine . NIST Handbook. 44 (2012 ed.). Washington, D.C.: U.S. Department of Commerce, Technology Administration, National Institute of Standards and Technology. ISSN 0271-4027 Archived 2022-12-25 at the Wayback Machine . OCLC OCLC   58927093. Retrieved 30 June 2012.
  17. Judson, Lewis V. (March 1976) [October 1963]. "8. Refinement of values for the yard and pound". Weights and Measures Standards of the United States: A brief history (PDF). NBS Special Publication. Vol. 447. Washington, D.C.: U.S. Department of Commerce, National Bureau of Standards. p. 20. OCLC   610190761. Archived from the original (PDF) on 3 June 2011. Retrieved 30 June 2012.
  18. "Consolidated TEXT: 31980L0181 — EN — 13.06.2020".
  19. Kelly, Patric (1835). Universal Cambist. London.
  20. A new English dictionary on historical principles: founded mainly on the materials collected by the Philological Society. Philological Society (Great Britain). 1891. p. 675 via Clarendon Press.
  21. Miege, Guy (1738). The Present State of Great Britain and Ireland. J. Brotherton, A. Bettesworth and C. Hitch, G. Strahan, W. Mears, R. Ware, E. Symon, and J. Clark. p. 307.