Grain (unit)

Last updated
Gold grain size comparison.jpg
The small golden disk close to the 5 cm marker is a piece of pure gold weighing one troy grain. Shown for comparison is a tape measure and coins of major world currencies.
General information
Unit system Troy weight, avoirdupois weight, apothecaries' weight
Unit ofMass
1 gr in ...... is equal to ...
   Troy   15760 troy pound
   Avoirdupois   17000 pound
   Apothecaries'   15760 apothecaries' pound
   SI units   64.79891 mg

A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and Apothecaries' system, 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. [1] :27 [2] Another source states that it was defined as the weight needed for 252.458 units to balance a cubic inch of distilled water at 30 inches of mercury pressure and 62 degrees Fahrenheit for both the air and water. [3] Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally. [4]


The grain was the legal foundation of traditional English weight systems, [5] and is the only unit that is equal throughout the troy, avoirdupois, and apothecaries' systems of mass. [6] :C-6 The unit was based on the weight of a single grain of barley, considered equivalent to 1+13 grains of wheat. [5] [7] :95 The fundamental unit of the pre-1527 English weight system known as Tower weights, was a different sort of grain known as the "wheat grain". [8] The Tower wheat grain was defined as exactly 4564 of a troy grain. [1] :74

Since the implementation of the international yard and pound agreement of 1 July 1959, the grain or troy grain (symbol: gr) measure has been defined in terms of units of mass in the International System of Units as precisely 64.79891  milligrams . [6] :C-19 [9] 1 gram is approximately 15.43236 grains. [6] :C-13 The unit formerly used by jewellers to measure pearls, diamonds, and other precious stones, called the jeweller's grain or pearl grain, is equal to 14 of a carat, or 50 mg (~0.7716 gr). [5] The grain was also the name of a traditional French unit equal to 53.115 mg. [5]

In both British Imperial and U.S. customary units, there are precisely 7,000 grains per avoirdupois pound, and 5,760 grains per troy pound or apothecaries pound. [6] :C-6–C-7

Current usage

A box of .38 Special (9.7 mm) cartridges that have 148-grain (9.6 g) bullets 148 grain 38 special.jpg
A box of .38 Special (9.7 mm) cartridges that have 148-grain (9.6 g) bullets

The grain is commonly used to measure the mass of bullets and propellants. [10] [11] In archery, the grain is the standard unit used to weigh arrows. [12]

In dentistry, gold foil, used as a material to restore teeth, [13] is measured in grains. [14] [15]

In North America, the hardness of water is often measured in grains per US gallon (gpg) of calcium carbonate equivalents. [16] [17] Otherwise, water hardness is measured in the dimensionless unit of parts per million (ppm), numerically equivalent to density measured in mg/L. [16] [17] One grain per US gallon is approximately 17.1 ppm. [16] [note] Soft water contains 1–4 gpg of calcium carbonate equivalents, while hard water contains 11–20 gpg. [17]

A five-grain aspirin. The usage guidance label on a bottle of aspirin indicates that the dosage is "325 mg (5 gr)". 5 grain aspirin.jpg
A five-grain aspirin. The usage guidance label on a bottle of aspirin indicates that the dosage is "325 mg (5 gr)".

Though no longer recommended, in the U. S. grains are still used occasionally in medicine as part of the apothecaries' system, especially in prescriptions for older medicines such as aspirin or phenobarbital. [18] [19] For example, the dosage of a standard 325 mg tablet of aspirin is sometimes given as 5 grains. [18] [20] In that example the grain is approximated to 65 mg, though the grain can also be approximated to 60 mg, depending on the medication and manufacturer. [18] [21] The apothecaries' system has its own system of notation, in which the unit's symbol or abbreviation is followed by the quantity in lower case Roman numerals. [19] [21] [22] For amounts less than one, the quantity is written as a fraction, or for one half, ss (or variations such as ss., ṡṡ, or s̅s̅). [19] [21] [22] [23] :263 Therefore, a prescription for tablets containing 325 mg of aspirin and 30 mg of codeine can be written "ASA gr. v c̄ cod. gr. ss tablets" (using the medical abbreviations ASA for aspirin, [23] :34 [24] :8 c̄ for "with", [23] :56 [24] :14 and cod. for codeine). [23] :70 [24] :19 The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare. [21]

In the U.S., particulate emission levels, used to monitor and regulate pollution, are commonly measured in grains per cubic foot instead of the more usual parts per million (ppm). [25] [26] This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity. [27] The SI unit used to measure particulate emissions and absolute humidity is mg/m3. [25] [27] One grain per cubic foot is approximately 2288 mg/m3. [note]


carob seed≈200 mg
barley grain≈65 mg
wheat grain≈50 mg

At least since antiquity, grains of wheat or barley were used by Mediterranean traders to define units of mass; along with other seeds, especially those of the carob tree. According to a longstanding tradition, 1 carat (the mass of a carob seed) was equivalent to the weight of 4 wheat grains or 3 barleycorns. [7] :95 Since the weights of these seeds are highly variable, especially that of the cereals as a function of moisture, this is a convention more than an absolute law. [28] :120–1

The history of the modern British grain can be traced back to a royal decree in thirteenth century England, re-iterating decrees that go back as far as King Offa (eighth century). [29] The tower pound was one of many monetary pounds of 240 silver pennies.[ citation needed ]

By consent of the whole Realm the King's Measure was made, so that an English Penny, which is called the Sterling, round without clipping, shall weigh Thirty-two Grains of Wheat dry in the midst of the Ear; Twenty pennies make an Ounce; and Twelve Ounces make a Pound.

The pound in question is the Tower pound. The Tower pound, abolished in 1527, consisted of 12 ounces like the troy pound, but was 116 (≈6%) lighter. The weight of the original sterling pennies was 22½ troy grains, or 32 "Tower grains". [28] :116

Physical grain weights were made and sold commercially at least as late as the early 1900s, and took various forms, from squares of sheet metal to manufactured wire shapes and coin-like weights. [30]

The troy pound was only "the pound of Pence, Spices, Confections, as of Electuaries", as such goods might be measured by a troi or small balance. The old troy standard was set by King Offa's currency reform, was in full use in 1284 (Assize of Weights and Measures, King Edward I), but was restricted to currency (the pound of pennies) until it was abolished in 1527. This pound was progressively replaced by a new pound, based on the weight of 120 silver dirhems of 48 grains. The new pound used a barley-corn grain, rather than the wheat grain. [31]

Avoirdupois (goods of weight) refers to those things measured by the lesser but quicker balances: the bismar or auncel, the Roman balance, and the steelyard. The original mercantile pound of 25 shillings or 15 (tower) ounces was displaced by variously the pound of the Hanseatic League (16 tower ounces) and by the pound of the then-important wool trade (16 ounces of 437 grains). A new pound of 7680 grains was inadvertently created as 16 troy ounces, referring to the new troy rather than the old troy. Eventually, the wool pound won out. [31]

The avoirdupois pound was defined in prototype, rated as 6992 to 7004 grains. In the Imperial Weights and Measures Act of 1824, the avoirdupois pound was defined as 7000 grains exactly. The act of 1855 authorised Miller's new standards to replace those lost in the fire that destroyed the Houses of Parliament. The standard was an avoirdupois pound, the grain being defined as 1/7000 of it. [32]

The division of the carat into four grains survives in both senses well into the early twentieth century. For pearls and diamonds, weight is quoted in carats, divided into four grains. The carat was eventually set to 205 milligrams (1877), and later 200 milligrams. For touch or fineness of gold, the fraction of gold was given as a weight, the total being a solidus of 24 carats or 96 grains. [33]

See also


1. ^ The exact value of one grain per US gallon is 64.79891/3.785411784 mg/L (ppm). [6] :C-12,C-14
2. ^ The exact value of one grain per cubic foot is 64.79891/0.028316846592 mg/m3. [6] :C-10,C-14

Related Research Articles

Carat (mass)

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.

Imperial units System of units that were implemented on 1 January 1826 in the British Empire

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. The imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. The system came into official use across the British Empire in 1826. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, but imperial units are still used in the United Kingdom and some other countries formerly part of the British Empire. The imperial system developed from what were first known as English units, as did the related system of United States customary units.

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 System of units of measurement commonly used in the United States

United States customary units are a system of measurements commonly used in the United States since it was formalized 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. Subsequently, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.

Troy weight System of units of mass

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 weights are the grain, the pennyweight, the troy ounce, and the troy pound. The troy grain is equal to the grain-unit of the avoirdupois system, the troy ounce is heavier than the avoirdupois ounce, yet the troy pound is lighter than the avoirdupois pound.

The ounce is the name of several different units of mass, weight, or volume used in most British derived customary systems of measurement.

Avoirdupois system System of weights (more properly, mass) based on a pound of 16 ounces

The avoirdupois system is a measurement system of weights which 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, 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 – an ancient Roman coin, later used as the symbol of an old British penny.

Fluid ounce

A fluid ounce is a unit of volume typically used for measuring liquids. Various definitions have been used throughout history, but only two are still in common use: the British Imperial and the United States customary fluid ounce.


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.

Apothecaries system 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 recipes 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 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. Systems of measurement in use include the International System of Units (SI), the modern form of the metric system, the British imperial system, and the United States customary system.

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.

History of measurement Aspect of history

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.

Comparison of the imperial and US customary measurement systems

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.

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.

Before the introduction of the Metric system, one may divide the history of Indian systems of measurement into three main periods: the pre-Akbar's period, the period of the Akbar system, and the British colonial period.

Imperial and US customary measurement systems

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 1826, 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 McDonald, Daniel McLean; Scarre, Christopher (1992). The origins of metrology: collected papers of Dr. Daniel McLean McDonald. McDonald Institute for Archaeological Research. ISBN   9780951942000 . Retrieved 15 September 2012.
  2. R. D. Connor (1987). The weights and measures of England . H.M.S.O. p.  124. ISBN   978-0-11-290435-9 . Retrieved 2 February 2012.
  3. Universal Dictionary of Weights and Measures. Baltimore. 1850. Retrieved 2016-09-23.
  4. Oldberg, Oscar (1885). A Manual of Weights, Measures, and Specific Gravity. Chicago: author [C. J. Johnson, printer]. p.  87 . Retrieved 2016-09-24.
  5. 1 2 3 4 Rowlett, Russ (13 September 2001). "G". How Many? A Dictionary of Units of Measurement. Chapel Hill, North Carolina: University of North Carolina at Chapel Hill. grain (gr) [1–3]. Retrieved 4 July 2012.
  6. 1 2 3 4 5 6 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" (PDF). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. NIST Handbook. 44 (2012 ed.). Washington, D.C.: U.S. Department of Commerce, Technology Administration, National Institute of Standards and Technology. ISSN 0271-4027. OCLC OCLC   58927093. Retrieved 30 June 2012.
  7. 1 2 Ridgeway, William (1889). "Metrological Notes: III.- Had the People of Pre-historic Mycenae a Weight Standard?". The Journal of Hellenic Studies . London: The Council for the Society for the Promotion of Hellenic Studies. 10: 90–97. doi:10.2307/623588. ISSN   0075-4269. JSTOR   623588. OCLC   51205085.
  8. Zupko, Ronald Edward (1977). British weights & measures: a history from antiquity to the sixteenth century. University of Wisconsin Press. p. 11. ISBN   9780299073404 . Retrieved 18 December 2011.
  9. 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. 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.
  10. International Practical Shooting Confederation (2011). "Handgun Competition Rules (January 2012 ed.)" (PDF). Ontario, Canada: International Practical Shooting Confederation. p. 40. Retrieved 4 July 2012.
  11. Meyer, Rudolf; Köhler, Josef; Homburg, Axel (2007). "Grain". Explosives (Sixth, completely revised ed.). Weinheim: Wiley-VCH. p. 152. ISBN   978-3-527-31656-4. OCLC   255797039 . Retrieved 4 July 2012.
  12. Sorrells, Brian J. (2004). "The Right Equipment". Beginner's Guide to Traditional Archery (1st ed.). Mechanicsburg, PA: Stackpole Books. p. 23. ISBN   978-0-8117-3133-1. OCLC   474105699 . Retrieved 4 July 2012. Arrow weight is measured in grains
  13. Small, Bruce W.; Johnson, Warren (March 2006). "Gold Foil and Its Use in Modern Dentistry". Dentistry Today. Montclair, NJ. 25 (3): 92, 94, 96. ISSN   8750-2186. OCLC   60622136. PMID   16617798 . Retrieved 5 July 2012.
  14. Soratur, S.H. (2002). "Chapter 17: Direct Filling Gold—Cohesive Gold — Gold Foil". Essentials of Dental Materials (1st ed.). New Delhi: Jaypee Brothers. p. 217. ISBN   978-81-7179-989-3. OCLC   465910002 . Retrieved 5 July 2012.
  15. Manappallil, John J. (2003). "Chapter 11: Direct Gold Filling — Gold Foil". Basic Dental Materials (2nd ed.). New Delhi: Jaypee Brothers. p. 199. ISBN   978-81-8061-153-7. OCLC   257699731 . Retrieved 5 July 2012.
  16. 1 2 3 Wist, William; McEachern, Rod; Lehr, Jay H. (2009). "Chapter 8: Comparison of KCl and NaCl as Regenerant". Water Softening with Potassium Chloride: Process, Health, and Environmental Benefits. Hoboken, NJ: John Wiley & Sons. p. 116. ISBN   978-0-470-08713-8. OCLC   496960317 . Retrieved 4 July 2012.
  17. 1 2 3 Vaclavik, Vickie A.; Christian, Elizabeth W. (2008). "Chapter 2: Water — Water Hardness and Treatments". In Heldman, Dennis R. (ed.). Essentials of Food Science. Food Science Text Series (3rd ed.). New York; London: Springer. p. 29. ISBN   978-0-387-69939-4. OCLC   230744052.
  18. 1 2 3 Zentz, Lorraine C. (2010). "Chapter 1: Fundamentals of Math — Apothecary System". Math for Pharmacy Technicians. Sudbury, MA: Jones & Bartlett Learning. pp. 7–8. ISBN   978-0-7637-5961-2. OCLC   421360709 . Retrieved 5 July 2012.
  19. 1 2 3 Boyer, Mary Jo (2009). "UNIT 2 Measurement Systems: The Apothecary System". Math for Nurses: A Pocket Guide to Dosage Calculation and Drug Preparation (7th ed.). Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams & Wilkins. pp. 108–9. ISBN   978-0-7817-6335-6. OCLC   181600928 . Retrieved 2 July 2012.
  20. Howell, David C. (2010). "Chapter 12: Multiple Comparisons Among Treatment Means — 12.10 Trend Analysis". Statistical Methods for Psychology (7th ed.). Belmont, CA: Wadsworth, Cengage Learning. p. 402. ISBN   978-0-495-59784-1. OCLC   689547756 . Retrieved 5 July 2012.
  21. 1 2 3 4 Buchholz, Susan; Henke, Grace (2009). "Chapter 3: Metric, Apothecary, and Household Systems of Measurement — Apothecary System". Henke's Med-Math: Dosage Calculation, Preparation and Administration (6th ed.). Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams & Wilkins. pp. 55–6. ISBN   978-0-7817-7628-8. OCLC   181600929 . Retrieved 5 July 2012.
  22. 1 2 Pickar, Gloria D.; Swart, Beth; Graham, Hope; Swedish, Margaret (2012). "Appendix B: Apothecary System of Measurement". Dosage Calculations (2nd Canadian ed.). Toronto: Nelson Education. pp. 527–8. ISBN   978-0-17-650259-1. OCLC   693657704 . Retrieved 5 July 2012.
  23. 1 2 3 4 Biblis, Margaret M., ed. (1992). Dorland's Medical Abbreviations. Philadelphia, PA: Saunders. ISBN   978-0-7216-3751-8. OCLC   246565261 . Retrieved 5 July 2012.
  24. 1 2 3 Steen, Edwin Benzel (1971). Medical Abbreviations (3rd ed.). Philadelphia, PA: F.A. Davis. ISBN   978-0-7020-0360-8. OCLC   165344 . Retrieved 5 July 2012.
  25. 1 2 Averdieck, William J. (2005). "15 Continuous Particulate Monitoring — 15.1 Overview". In Down, Randy D.; Lehr, Jay H. (eds.). Environmental Instrumentation and Analysis Handbook. Hoboken, NJ: Wiley-Interscience. p. 330. ISBN   978-0-471-46354-2. OCLC   469979932 . Retrieved 5 July 2012.
  26. Chase, Craig L., ed. (1998). "Particulate Emissions". Biomass Energy: A Glossary of Terms. Western Regional Biomass Energy Program. DIANE Publishing. p. 40. ISBN   978-0-7881-7256-4. OCLC   256903828 . Retrieved 5 July 2012.
  27. 1 2 "Glossary: AA–AB". Offshore Energy and Minerals Management. Washington, D.C.: Bureau of Ocean Energy Management, Regulation and Enforcement, United States Department of the Interior. 17 September 2010. Archived from the original on 29 July 2012. Retrieved 5 July 2012.
  28. 1 2 3 Connor, R.D.; Simpson, A.D.C. (c. 2004). Weights and Measures in Scotland. East Linton.
  29. Zupko, Ronald Edward (1977). British Weights and Measures. Madison: University of Wisconsin. p. 11. ISBN   0-299-07340-8.
  30. "The Grains of History" . Retrieved 2016-09-21.
  31. 1 2 Watson, C. M. (1910). British Weights and Measures. London: John Murry. pp. 32–34.
  33. Woolhouse, W. S. B. (1890). Measures, Weights and Measures of all Nations. London: Crosby Lockwood and Son. p. 33.