Troy weight is a system of units of mass that originated in 15th-century England,  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 probably takes its name from the French market town of Troyes where English merchants traded at least as early as the early 9th century.   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.  
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. Watson finds the dialect word troi, meaning a balance in Wright's The English Dialect Dictionary. Troy weight referred to the tower system; the earliest reference to the modern troy weights is in 1414.  
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.  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.  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 use today 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.  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 about 1400 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. 
The troy ounce and grain were also part of the apothecaries' system. This was long used in medicine, but has now been largely replaced by the metric system (milligrams). 
The only troy weight in widespread use today is the British Imperial troy ounce and its American counterpart. Both are currently based on a grain of 0.06479891 gram (exact, by definition), with 480 grains to a troy ounce (compared with 437+1⁄2 grains for an ounce avoirdupois).
The British Empire abolished the 12-ounce troy pound in the 19th century, though it has been retained (although rarely used) in the American system. Larger amounts of precious metals are conventionally counted in hundreds or thousands of troy ounces (or in kilograms).
The origin of the troy weight system is unknown. Although the name probably comes from the Champagne fairs at Troyes, in northeastern France,  the units themselves may be of more northern origin.[ citation needed ] 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.) 
An alternative suggestion is that the weights come from the Muslim domains by way of the gold dirhem (47.966 British Imperial grains), in the manner that King Offa's weights were derived from the silver dirhem (about 45.0 British grains).
According to Watson, troy relates to a dialect word troi (balance). Then troy weight is a style of weighing, like auncel or bismar weights, or other kindred methods. The troy weight then refers to weighing of small precious or potent goods, such as bullion and medicines. 
Troy ounces have been and are still often used in precious metal markets in countries that otherwise use International System of Units (SI),   except in East Asia.  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.
The troy pound (lb t) consists of twelve troy ounces  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).
A troy ounce weighs 480 grains.  Since the implementation of the international yard and pound agreement of 1 July 1959, the grain measure is defined as precisely 64.79891 milligrams .  : C-19  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 480⁄437.5 = 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 
The pennyweight symbol is dwt. One pennyweight weighs 24 grains and 20 pennyweights make one troy ounce.  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, English pound sterling was based on the tower pound, which is 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 were indicated using the symbols £, s, and d, respectively.
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, 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.  
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In Scotland, the Incorporation of Goldsmiths of the City of Edinburgh used a system in multiples of sixteen. (See Assay-Master's Accounts, 1681–1702, on loan from the Incorporation to the National Archives of Scotland.)[ better source needed ] There were 16 drops to the troy ounce, 16 ounces to the Scottish troy pound, and 16 pounds to the stone. The Scots had several other ways of measuring precious metals and gems, but this was the common usage for gold and silver.
The Scottish pound was 7,716 grains,[ citation needed ] but after the union of Scotland with England, was reduced to 7,680 grains.[ citation needed ] This divides to 16 ounces, each of 16 drops, each of 30 grains. The reduction made the ounce and grain equal in mass to the English standard.
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. 
|Troy pound (12 troy ounces)||5,760||373.24172 16|
|Troy ounce (20 pennyweights)||480||31.10347 68|
|Avoirdupois||1||175/144||= 1.21527||35/27||= 1.296||28/27||= 1.037||35/36||= 0.972||≈ 0.9072||16||14+7/12||= 14.583||15+5/9||= 15.5||7,000||9,955+5/9||≈ 454||≈ 5/11|
|Troy||144/175||≈ 0.8229||1||16/15||= 1.06||64/75||= 0.853||4/5||= 0.8||≈ 0.7465||13+29/175||≈ 13.17||12||12+4/5||= 12.8||5,760||8,192||≈ 373||≈ 3/8|
|Tower||27/35||≈ 0.7714||15/16||= 0.9375||1||4/5||= 0.8||3/4||= 0.75||≈ 0.6998||12+12/35||≈ 12.34||11+1/4||= 11.25||12||5,400||7,680||≈ 350||≈ 7/20|
|Merchant||27/28||≈ 0.9643||75/64||= 1.171875||5/4||= 1.25||1||15/16||= 0.9375||≈ 0.8748||15+3/7||≈ 15.43||14+1/16||= 14.0625||15||6,750||9,600||≈ 437||≈ 7/16|
|London||36/35||≈ 1.029||5/4||= 1.25||4/3||= 1.3||16/15||= 1.06||1||≈ 0.9331||16+16/35||≈ 16.46||15||16||7,200||10,240||≈ 467||≈ 7/15|
|Metric||≈ 1.1023||≈ 1.3396||≈ 1.4289||≈ 1.1431||≈ 1.0717||1||≈ 17.64||≈ 16.08||≈ 17.15||7,716||10,974||= 500||= 1/2|
The troy system was used in the apothecaries' system, but with different further subdivisions.
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King Offa's 8th century currency reform replaced the sceat with the silver penny.[ citation needed ] This coin was derived from half of a silver dirhem.[ citation needed ] The masses were then derived by a count of coins, by a mix of Charlemagne and Roman systems. An ounce was set as twenty pence,[ citation needed ] and a pound to twelve ounces or 240 silver pence.[ citation needed ] In practice, the weights of the coins was not consistent and 240 of them seldom added up to a full pound; there were no shilling or pound coins and the pound as used only as an accounting convenience. 
Later kings debased the coin, both in weight and fineness. The original pound divided was the tower pound of 5,400 grains, but a later pound of 5,760 grains displaced it. Where once 240 pence made a tower pound (and 256 make a troy pound), by the time of the United Kingdom Weights and Measures Act of 1824, a troy pound gives 792 silver pence, still minted as such as Maundy Money.
The carat (ct) is a unit of mass equal to 200 mg (0.00705 oz) or 0.00643 troy oz, and 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.
The pound or pound-mass is a unit of mass used in 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 ″̶.
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 which 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 significant differences between the systems.
The standard circulating coinage of the United Kingdom, British Crown Dependencies and British Overseas Territories is denominated in pennies and pounds sterling, and ranges in value from one penny sterling to two pounds. Since decimalisation, on 15 February 1971, the pound has been divided into 100 (new) pence. Before decimalisation, twelve pence made a shilling, and twenty shillings made a pound.
A penny is a coin or a unit of currency in various countries. Borrowed from the Carolingian denarius, it is usually the smallest denomination within a currency system. Presently, it is the formal name of the British penny (abbr. p) and the de facto name of the American one-cent coin (abbr. ¢) as well as the informal Irish designation of the 1 cent euro coin (abbr. c). Due to inflation, pennies have lost virtually all their purchasing power and are often viewed as an expensive burden to merchants, banks, government mints and the public in general.
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, essentially the premodern equivalent of legal boilerplate. 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.
The English penny, originally a coin of 1.3 to 1.5 grams pure silver, was introduced c. 785 by King Offa of Mercia. These coins were similar in size and weight to the continental deniers of the period and to the Anglo-Saxon sceats which had preceded it.
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.
A pennyweight (dwt) is a unit of mass equal to 24 grains, 1⁄20 of a troy ounce, 1⁄240 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.
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.
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.
The fineness of a precious metal object represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
English units are 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.
Both the British Imperial and United States customary systems of measurement derive from earlier English systems used in the Middle Ages, that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units brought by William the Conqueror after the Norman Conquest of England in 1066.
Silver coins are considered the oldest mass-produced form of coinage. Silver has been used as a coinage metal since the times of the Greeks; their silver drachmas were popular trade coins. The ancient Persians used silver coins between 612–330 BC. Before 1797, British pennies were made of silver.
Winchester measure is a set of legal standards of volume instituted in the late 15th century (1495) by King Henry VII of England and in use, with some modifications, until the present day. It consists of the Winchester bushel and its dependent quantities, the peck, (dry) gallon and (dry) quart. They would later become known as the Winchester Standards, named because the examples were kept in the city of Winchester.
The Great Recoinage of 1816 was an attempt by the government of the United Kingdom of Great Britain and Ireland to re-stabilise its currency, the pound sterling, after the economic difficulties brought by the French Revolutionary Wars and the Napoleonic Wars.
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 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.
The received opinion is that it took its name from a weight used at the fair of Troyes in France
…the great fairs established for all Europe the weight-standard Troyes, whence…Troy…
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.
Anglo-Saxon King Offa is credited with introducing the system of money to central and southern England in the latter half of the 8th Century, overseeing the minting of the earliest English silver pennies –emblazoned with his name. In practice they varied considerably in weight and 240 of them seldom added up to a pound. There were at that time no larger denomination coins – pounds and shillings were merely useful units of account.