View source for Grain (unit)

{{Short description|Unit of mass}}
{{Infobox unit
| bgcolor = 
| name = Grain
| image = Gold grain size comparison.jpg
| caption = The small golden disc 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.
| standard = [[Troy weight]], avoirdupois weight, apothecaries' weight
| quantity = Mass
| symbol = gr
| units1 = Troy
| inunits1 = {{frac|5760}} troy pound
| units2 = Avoirdupois
| inunits2 = {{frac|7000}} pound
| units3 = Apothecaries'
| inunits3 = {{frac|5760}} apothecaries' pound
| units4 = SI units
| inunits4 = {{convert|1|gr|mg|sigfig=7|disp=out}}
}}
A '''grain''' is a unit of measurement of [[Physics:Mass|mass]], and in the [[Troy weight|troy weight]], [[Avoirdupois|avoirdupois]], and [[Apothecaries' system|apothecaries' system]]s, equal to exactly {{val|64.79891|u=milligrams}}. It is nominally based upon the mass of a single ideal seed of a [[Biology:Cereal|cereal]]. From the Bronze Age into the Renaissance, the average masses of [[Biology:Wheat|wheat]] and [[Biology:Barley|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.<ref name="McDonaldScarre1992">{{cite book|last1=McDonald|first1=Daniel McLean|last2=Scarre|first2=Christopher|title=The origins of metrology: collected papers of Dr. Daniel McLean McDonald|url=https://books.google.com/books?id=8ujaAAAAMAAJ|access-date=15 September 2012|year=1992|publisher=McDonald Institute for Archaeological Research|isbn=9780951942000}}</ref>{{rp|27}}<ref name="Connor1987">{{cite book|author=R. D. Connor|title=The weights and measures of England|url=https://archive.org/details/weightsmeasureso0000conn|url-access=registration|access-date=2 February 2012|year=1987|publisher=H.M.S.O.|isbn=978-0-11-290435-9|page=[https://archive.org/details/weightsmeasureso0000conn/page/124 124]}}</ref> Another source states that it was defined such that 252.458 units would balance {{convert|1|cuin|cm3}} of distilled water at an ambient air-water pressure and temperature of {{convert|30|inHg|kPa}} and {{convert|62|F|C}} respectively.<ref>{{cite book|title=Universal Dictionary of Weights and Measures |date=1850 |location=Baltimore |url=https://archive.org/stream/universaldictio01alexgoog#page/n146/mode/2up|access-date=2016-09-23}}</ref> Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally.<ref>{{cite book|title=A Manual of Weights, Measures, and Specific Gravity |publisher=author [C. J. Johnson, printer] |last=Oldberg |first=Oscar |date=1885 |location=Chicago |url=https://archive.org/details/amanualweightsm00oldbgoog |page=[https://archive.org/details/amanualweightsm00oldbgoog/page/n100 87] |access-date=2016-09-24}}</ref>

The grain was the legal foundation of traditional English weight systems,<ref name="Rowlett2001">{{cite web |url=http://www.unc.edu/~rowlett/units/dictG.html |title=G |first=Russ |last=Rowlett |date=13 September 2001 |work=How Many? A Dictionary of Units of Measurement |publisher=[[Organization:University of North Carolina at Chapel Hill|University of North Carolina at Chapel Hill]] |location=Chapel Hill, North Carolina |at=grain (gr) [1–3] |access-date=4 July 2012}}</ref> and is the only unit that is equal throughout the troy, avoirdupois, and apothecaries' systems of mass.<ref name="NIST" />{{rp|C-6}} The unit was based on the weight of a single grain of barley which was equal to about {{frac||4|3}} the weight of a single grain of wheat.<ref name="Rowlett2001" /><ref name="Ridgeway1889" />{{rp|95}} The fundamental unit of the pre-1527 English weight system, known as [[English units#Troy and Tower|Tower weights]], was based on the wheat grain.<ref>{{cite book|last=Zupko|first=Ronald Edward|title=British weights & measures: a history from antiquity to the sixteenth century|url=https://books.google.com/books?id=pWUgAQAAIAAJ |access-date=18 December 2011|year=1977|publisher=University of Wisconsin Press|page=11|isbn=9780299073404}}</ref> The tower "wheat" grain was defined as exactly {{frac||45|64}} (≈{{frac||3|4}}) of the troy "barley" grain.<ref name="McDonaldScarre1992" />{{rp|74}}

Since the implementation of the [[International yard and pound|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 {{val|64.79891|u=milligrams}}.<ref name="NIST">National Institute of Standards and Technology (October 2011). Butcher, Tina; Cook, Steve; Crown, Linda et al. eds. [https://www.nist.gov/pml/wmd/pubs/upload/AppC-12-hb44-final.pdf "Appendix C – General Tables of Units of Measurement"] (PDF). [https://www.nist.gov/pml/wmd/pubs/h44-12.cfm ''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. [[International Standard Serial Number|ISSN]] [http://www.worldcat.org/issn/0271-4027 0271-4027]. OCLC {{OCLC|58927093}}. Retrieved 30 June 2012.</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> One gram is thus approximately equivalent to {{val|15.43236|u=grains}}.<ref name="NIST" />{{rp|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 {{convert|1/4|carat|mg gr}}.<ref name="Rowlett2001" /> The grain was also the name of a traditional [[Physics:Units of measurement in France|French unit]] equal to {{val|53.115|u=mg}}.<ref name="Rowlett2001" />

In both [[Imperial units|British Imperial units]] and United States customary units, there are precisely 7,000 grains per avoirdupois pound, and 5,760 grains per troy pound or apothecaries' pound.<ref name="NIST" />{{rp|C-6–C-7}} It is obsolete in the United Kingdom and, like most other non-SI units, it has no basis in law and cannot be used in commerce.<ref>{{cite web |url=https://www.gov.uk/weights-measures-and-packaging-the-law |title= Weights and measures: the law |website=UK Government |accessdate=2021-11-11}}</ref>

== Current usage ==
[[Image:148 grain 38 special.jpg|thumb|250px|A box of .38 Special ({{convert|0.357|in|mm|disp=out}}) cartridges that have {{convert|148|gr|g|adj=on}} bullets]]

Grains are commonly used to measure the mass of bullets and [[Physics:Propellant|propellant]]s.<ref>{{cite web |url=http://www.ipsc.org/pdf/RulesHandgun.pdf |title=Handgun Competition Rules (January 2012 ed.) |author=International Practical Shooting Confederation |year=2011 |publisher=International Practical Shooting Confederation |location=Ontario, Canada |page=40 |access-date=4 July 2012}}</ref><ref name="MeyerEtAl2007">{{cite book |last1=Meyer |first1=Rudolf |last2=Köhler |first2=Josef |last3=Homburg |first3=Axel |title=Explosives |url=https://books.google.com/books?id=ATiYCfo1VcEC |access-date=4 July 2012 |edition=Sixth, completely revised |year=2007 |publisher=Wiley-VCH |location=Weinheim |isbn=978-3-527-31656-4 |oclc=255797039 |page=152 |chapter=Grain |chapter-url=https://books.google.com/books?id=ATiYCfo1VcEC&pg=PA152}}</ref> In archery, the grain is the standard unit used to weigh arrows.<ref>{{cite book |last=Sorrells |first=Brian J. |title=Beginner's Guide to Traditional Archery |url=https://books.google.com/books?id=P5miJc4EbYwC |access-date=4 July 2012 |edition=1st |year=2004 |publisher=Stackpole Books |location=Mechanicsburg, PA |isbn=978-0-8117-3133-1 |oclc=474105699 |page=23 |chapter=The Right Equipment |chapter-url=https://books.google.com/books?id=P5miJc4EbYwC&pg=PA23 |quote=Arrow weight is measured in grains}}</ref>

In North America, the hardness of water is often measured in grains per US gallon (gpg) of [[Chemistry:Calcium carbonate|calcium carbonate]] equivalents.<ref name="WistEtAl2007">{{cite book |last1=Wist |first1=William |last2=McEachern |first2=Rod |last3=Lehr |first3=Jay H. |title=Water Softening with Potassium Chloride: Process, Health, and Environmental Benefits |url=https://books.google.com/books?id=GJbdjEvQd1kC |access-date=4 July 2012 |year=2009 |publisher={{wipe|John Wiley & Sons}} |location=Hoboken, NJ |isbn=978-0-470-08713-8 |oclc=496960317 |page=116 |chapter=Chapter 8: Comparison of KCl and NaCl as Regenerant |chapter-url=https://books.google.com/books?id=GJbdjEvQd1kC&pg=PA116}}</ref><ref name="VaclavikEtAl2008">{{cite book|author1=Vaclavik, Vickie A.|author2=Christian, Elizabeth W. |year=2008 |chapter-url=https://books.google.com/books?id=iCCsvwZrguUC&pg=PA29 |chapter=Chapter 2: Water — Water Hardness and Treatments|title=Essentials of Food Science |edition=3rd |editor=Heldman, Dennis R. |series=Food Science Text Series|location=New York; London|publisher=[[Company:Springer Science+Business Media|Springer]] |page=29|isbn=978-0-387-69939-4|oclc=230744052}}</ref> Otherwise, water hardness is measured in the dimensionless unit of [[Parts per million|parts per million]] (ppm), numerically equivalent to concentration measured in milligrams per litre.<ref name="WistEtAl2007" /><ref name="VaclavikEtAl2008" /> One grain per US gallon is approximately {{val|17.1|u=ppm}}.<ref name="WistEtAl2007" />{{ref|ppm|[''note'']}} Soft water contains 1–4&nbsp;gpg of calcium carbonate equivalents, while hard water contains 11–20&nbsp;gpg.<ref name="VaclavikEtAl2008" />

[[Image:5 grain aspirin.jpg|thumb|250px|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|apothecaries' system]], especially in prescriptions for older medicines such as [[Chemistry:Aspirin|aspirin]] or [[Chemistry:Phenobarbital|phenobarbital]].<ref name="Zentz2010">{{cite book |last=Zentz |first=Lorraine C. |title=Math for Pharmacy Technicians |url=https://books.google.com/books?id=PvriGp6ZEhMC |access-date=5 July 2012 |year=2010 |publisher=Jones & Bartlett Learning |location=Sudbury, MA |isbn=978-0-7637-5961-2 |oclc=421360709 |pages=7–8 |chapter=Chapter 1: Fundamentals of Math — Apothecary System |chapter-url=https://books.google.com/books?id=PvriGp6ZEhMC&pg=PA7}}</ref><ref name="Boyer2009">{{cite book |last=Boyer |first=Mary Jo |title=Math for Nurses: A Pocket Guide to Dosage Calculation and Drug Preparation |url=https://books.google.com/books?id=FCfCGwqNt4QC |access-date=2 July 2012 |edition=7th |year=2009 |publisher=Wolters Kluwer Health {{pipe}} Lippincott Williams & Wilkins |location=Philadelphia, PA |isbn=978-0-7817-6335-6 |oclc=181600928 |pages=108–9 |chapter=UNIT 2 Measurement Systems: The Apothecary System |chapter-url=https://books.google.com/books?id=FCfCGwqNt4QC&pg=PA108}}</ref> For example, the dosage of a standard {{val|325|u=mg}} tablet of aspirin is sometimes given as {{val|5|u=grains}}.<ref name="Zentz2010" /><ref name="Howell2010">{{cite book |last=Howell |first=David C. |title=Statistical Methods for Psychology |url=https://books.google.com/books?id=5WFohzuwzP0C |access-date=5 July 2012 |edition=7th |year=2010 |publisher=Wadsworth, Cengage Learning |location=Belmont, CA |isbn=978-0-495-59784-1 |oclc=689547756 |page=402 |chapter=Chapter 12: Multiple Comparisons Among Treatment Means — 12.10&nbsp;Trend Analysis |chapter-url=https://books.google.com/books?id=5WFohzuwzP0C&pg=PA402}}</ref> In that example the grain is approximated to {{val|65|u=mg}}, though the grain can also be approximated to {{val|60|u=mg}}, depending on the medication and manufacturer.<ref name="Zentz2010" /><ref name="Buchholz2009" /> 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]].<ref name="Boyer2009" /><ref name="Buchholz2009">{{cite book |last1=Buchholz |first1=Susan |last2=Henke |first2=Grace |title=Henke's Med-Math: Dosage Calculation, Preparation and Administration |url=https://books.google.com/books?id=ZlKqGHGNrtIC |access-date=5 July 2012 |edition=6th |year=2009 |publisher=Wolters Kluwer Health {{pipe}} Lippincott Williams & Wilkins |location=Philadelphia, PA |isbn=978-0-7817-7628-8 |oclc=181600929 |pages=55–6 |chapter=Chapter 3: Metric, Apothecary, and Household Systems of Measurement — Apothecary System |chapter-url=https://books.google.com/books?id=ZlKqGHGNrtIC&pg=PA55}}</ref><ref name="PickarEtAl2012">{{cite book |last1=Pickar |first1=Gloria D. |last2=Swart |first2=Beth |last3=Graham |first3=Hope |last4=Swedish |first4=Margaret |title=Dosage Calculations |url=https://books.google.com/books?id=wFEsup6KhuQC |access-date=5 July 2012 |edition=2nd Canadian |year=2012 |publisher=Nelson Education |location=Toronto |isbn=978-0-17-650259-1 |oclc=693657704 |pages=527–8 |chapter=Appendix B: Apothecary System of Measurement |chapter-url=https://books.google.com/books?id=wFEsup6KhuQC&pg=PA527}}</ref> 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).<ref name="Boyer2009" /><ref name="Buchholz2009" /><ref name="PickarEtAl2012" /><ref name="Biblis1992">{{cite book |editor-first=Margaret M. |editor-last=Biblis |title=Dorland's Medical Abbreviations |url=https://books.google.com/books?id=iFZqAAAAMAAJ |access-date=5 July 2012 |year=1992 |publisher=Saunders |location=Philadelphia, PA |isbn=978-0-7216-3751-8 |oclc=246565261}}</ref>{{rp|263}} Therefore, a prescription for tablets containing 325&nbsp;mg of aspirin and 30&nbsp;mg of codeine can be written "ASA gr. v c̄ cod. gr. ss tablets" (using the medical abbreviations ASA for acetylsalicylic acid [aspirin],<ref name="Biblis1992" />{{rp|34}}<ref name="Steen1971">{{cite book |last=Steen |first=Edwin Benzel |title=Medical Abbreviations |url=https://books.google.com/books?id=LWvKBnlAY_4C |access-date=5 July 2012 |edition=3rd |year=1971 |publisher=F.A. Davis |location=Philadelphia, PA |isbn=978-0-7020-0360-8 |oclc=165344}}</ref>{{rp|8}} c̄ for "with",<ref name="Biblis1992" />{{rp|56}}<ref name="Steen1971" />{{rp|14}} and cod. for codeine).<ref name="Biblis1992" />{{rp|70}}<ref name="Steen1971" />{{rp|19}} The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare.<ref name="Buchholz2009" />

In the U.S., particulate emission levels, used to monitor and regulate pollution, are sometimes measured in grains per cubic foot instead of the more usual ppm by volume.<ref name="Averdieck2005">{{cite book |last=Averdieck |first=William J. |editor1-first=Randy D. |editor1-last=Down |editor2-first=Jay H. |editor2-last=Lehr |title=Environmental Instrumentation and Analysis Handbook |url=https://books.google.com/books?id=6jhELyGJOm0C |access-date=5 July 2012 |year=2005 |publisher=Wiley-Interscience |location=Hoboken, NJ |isbn=978-0-471-46354-2 |oclc=469979932 |page=330 |chapter=15 Continuous Particulate Monitoring — 15.1 Overview |chapter-url=https://books.google.com/books?id=6jhELyGJOm0C&pg=PA330}}</ref><ref>{{cite book |editor-first=Craig L. |editor-last=Chase |title=Biomass Energy: A Glossary of Terms |url=https://books.google.com/books?id=NT3JvB4JWYUC |access-date=5 July 2012 |series=Western Regional Biomass Energy Program |year=1998 |publisher=DIANE Publishing |isbn=978-0-7881-7256-4 |oclc=256903828 |page=40 |chapter=Particulate Emissions |chapter-url=https://books.google.com/books?id=NT3JvB4JWYUC&pg=PA40}}</ref> This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity.<ref name="BOEMRE2010">{{cite web|url=http://www.boemre.gov/glossary/aa-ab.htm |title=Glossary: AA–AB |access-date=5 July 2012 |date=17 September 2010 |work=Offshore Energy and Minerals Management |publisher=Bureau of Ocean Energy Management, Regulation and Enforcement, United States Department of the Interior |location=Washington, D.C. |url-status=dead |archive-url=https://web.archive.org/web/20120729121218/http://www.boemre.gov/glossary/aa-ab.htm |archive-date=29 July 2012 }}</ref> The SI unit used to measure particulate emissions and absolute humidity is mg/[[Cubic metre|m{{sup|3}}]].<ref name="Averdieck2005" /><ref name="BOEMRE2010" /> One grain per cubic foot is approximately {{val|2288|u=mg/m{{sup|3}}}}.{{ref|mgm3|[''note'']}}

== History ==
{|class=wikitable align=right
|carob seed||≈200&nbsp;mg
|-
|barley grain||≈65&nbsp;mg
|-
|wheat grain||≈50&nbsp;mg
|}
At least since [[History:Classical antiquity|antiquity]], grains of [[Biology:Wheat|wheat]] or [[Biology:Barley|barley]] were used by Mediterranean traders to define units of mass; along with other seeds, especially those of the [[Biology:Carob|carob]] tree. According to a longstanding tradition, one carat (the mass of a carob seed) was equivalent to the weight of four wheat grains or three barleycorns.<ref name="Ridgeway1889">{{cite journal |last=Ridgeway |first=William |title=Metrological Notes: III.- Had the People of Pre-historic Mycenae a Weight Standard? |journal=The Journal of Hellenic Studies |volume=10 |year=1889 |pages=90–97 |publisher=The Council for the Society for the Promotion of Hellenic Studies |location=London |issn=0075-4269 |oclc=51205085 |doi=10.2307/623588 |jstor=623588|s2cid=164030519 |url=https://zenodo.org/record/1449896 }}</ref>{{rp|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.<ref name="wms">{{cite book |last=Connor |first=R.D. |author2=Simpson, A.D.C. |title=Weights and Measures in Scotland |location=East Linton |year=c. 2004}}</ref>{{rp|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).<ref>{{cite book|last=Zupko|first=Ronald Edward|title=British Weights and Measures|year=1977|publisher=University of Wisconsin |location=Madison |isbn=0-299-07340-8|pages=11}}</ref> The Tower pound was one of many monetary pounds of 240 silver pennies.{{Citation needed|date=January 2021}}

{{Quote|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.|[[Weights and Measures Acts (UK)#Acts of Parliament|Tractatus de Ponderibus et Mensuris]]<ref name="wms" />{{rp|119}}}}

The pound in question is the Tower pound. The Tower pound, abolished in 1527, consisted of 12 [[Ounce|ounce]]s like the troy pound, but was {{frac|16}} (≈6%) lighter. The weight of the original sterling pennies was 22½ troy grains, or 32 "Tower grains".<ref name="wms" />{{rp|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.<ref>{{cite web|title=The Grains of History |url=http://www.apothecariesweights.com/articles/the-grains-of-history/ |access-date=2016-09-21}}</ref>

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, and 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 a wheat grain.<ref name=watson1910>{{cite book|last=Watson|first=C. M.|title=British Weights and Measures as described in the laws of England from Anglo-Saxon times|year=1910|publisher=John Murray|location=London|pages=32–34|url=https://archive.org/details/britishweightsme00watsuoft}}</ref>

Avoirdupois (goods of weight) refers to those things measured by the lesser but quicker balances: the bismar or auncel, the Roman balance, and the [[Engineering:Steelyard balance|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 {{val|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.<ref name="watson1910"/>

The avoirdupois pound was defined in prototype, rated as {{val|6992}} to {{val|7004}} grains. In the Imperial Weights and Measures Act of 1824, the avoirdupois pound was defined as {{val|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 {{sfrac|{{val|7000}}}} of it.<ref>{{Cite web|url=http://www.global-converter.com/unit-to-unit/pound-avoirdupois-pound-mass-to-grain-avoirdupois-mass-converter/|title = Pound (Avoirdupois, pound-mass) to grain (Avoirdupois) conversion &#124; Units of Mass}}</ref>

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.<ref name=Woodhouse>{{cite book|last=Woolhouse|first=W. S. B.|title=Measures, Weights and Measures of all Nations|year=1890|publisher=Crosby Lockwood and Son|location=London|page=33|url=https://archive.org/details/measuresweights00woolgoog/page/n6/mode/2up}}</ref>

== See also ==
* English unit

== Notes ==
:1.{{note|ppm}}The exact value of one grain per US gallon is {{sfrac|{{val|64.79891}}|{{val|3.785411784}}}}&nbsp;mg/L (ppm).<ref name="NIST" />{{rp|C-12,C-14}}
:2.{{note|mgm3}}The exact value of one grain per cubic foot is {{sfrac|{{val|64.79891}}|{{val|0.028316846592}}}}&nbsp;mg/m<sup>3</sup>.<ref name="NIST" />{{rp|C-10,C-14}}

== References ==
{{Reflist|30em}}

{{Imperial units}}

[[Category:Units of mass]]
[[Category:Imperial units]]
[[Category:Customary units of measurement in the United States]]

{{Sourceattribution|Grain (unit)}}