|Unit system||UCUM base unit and CGS unit|
|1 g in ...||... is equal to ...|
|SI base units||10−3kilograms|
|CGS units||1 gram|
| Imperial units|
Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre [1 cm3], and at the temperature of melting ice" (later at 4 degrees Celsius, the temperature of maximum density of water). However, in a reversal of reference and defined units, a gram is now defined as one thousandth of the SI base unit, the kilogram, or 1×10−3 kg, which itself is defined by the International Bureau of Weights and Measures, not in terms of grams, but by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 kg⋅m2⋅s−1.
The only unit symbol for gram that is recognised by the International System of Units (SI) is "g" following the numeric value with a space, as in "640 g" to stand for "640 grams" in the English language. The SI does not support the use of abbreviations such as "gr" (which is the symbol for grains),:C-19 "gm" ("g⋅m" is the SI symbol for gram-metre) or "Gm" (the SI symbol for gigametre).
The word gramme was adopted by the French National Convention in its 1795 decree revising the metric system as replacing the gravet introduced in 1793. Its definition remained that of the weight (poids) of a cubic centimetre of water.
French gramme was taken from the Late Latin term gramma. This word—ultimately from Greek γράμμα (grámma), "letter"—had adopted a specialised meaning in Late Antiquity of "one twenty-fourth part of an ounce" (two oboli), corresponding to about 1.14 modern grams. This use of the term is found in the carmen de ponderibus et mensuris ("poem about weights and measures") composed around 400 AD.[a] There is also evidence that the Greek γράμμα was used in the same sense at around the same time, in the fourth century, and survived in this sense into Medieval Greek, while the Latin term did not remain current in Medieval Latin and was recovered in Renaissance scholarship.[b]
The gram was the fundamental unit of mass in the nineteenth-century centimetre–gram–second system of units (CGS). The CGS system co-existed with the MKS system of units, first proposed in 1901, during much of the 20th century, but the gram has been displaced by the kilogram as the fundamental unit for mass when the MKS system was chosen for the SI base units in 1960.
Most standards and legal requirements for nutrition labels on food products require relative contents to be stated per 100 g of the product, such that the resulting figure can also be read as a percentage by weight.
- 1 gram (g) = 15.4323583529 grains (gr)
- 1 grain (gr) = 0.06479891 grams (g)
- 1 avoirdupois ounce (oz) = 28.349523125 grams (g)
- 1 troy ounce (ozt) = 31.1034768 grams (g)
- 100 grams (g) = 3.527396195 ounces
- 1 gram (g) = 5 carats (ct)
- 1 gram (g) = 8.98755179×1013joules (J) (by mass–energy equivalence)
- 1 undecimogramme = 1 "eleventh-gram" = 10−11 grams in the historic quadrant–eleventh-gram–second system (QES system) a.k.a. hebdometre–undecimogramme–second system (HUS system) (HUS system) 
- 500 grams (g) = 1 Jin in the Chinese units of measurement.
- This list was truncated from 9 items.
- The date and authorship of this Late Latin didactic poem are both uncertain; it was attributed to Priscian but is now attributed to Rem(m)ius Favinus/Flav(in)us. The poem's title is reflected in the French phrase poids et mesures ("weights and mesures") in the title of the 1795 National Convention decree, Decret relatif aux poids et aux mesures that introduced the gram, and indirectly in the name of the General Conference on Weights and Measures responsible for the modern definition of the metric units.
- In the Renaissance, the carmen de ponderibus et mensuris was received as a work of the first-century grammarian Remmius Palaemon edited in 1528 by Johann Setzer of Hagenau, together with works by Celsius, Priscian and Johannes Caesarius; Aurelij Cornelij Celsi, De re medica, libri octo eruditissimi. Q. Sereni Samonici Praecepta medica, uersibus hexametris. Q. Rhemnij Fannij Palaemonis, De ponderibus [et] mensuris, liber rarus [et] utilissimus
- "Weights and Measures Act 1985 (c. 72)". The UK Statute Law Database. Office of Public Sector Information. Archived from the original on 12 September 2008. Retrieved 26 January 2011.
- "Decret relatif aux poids et aux mesures" (in French). 1795. Archived from the original on 25 February 2013.
- Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 20-6th meeting (2018) (PDF)
- Decision CIPM/105-13 (October 2016). The day is the 140-4th anniversary of the Metre Convention.
- 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. OCLC OCLC 58927093. Retrieved 30 June 2012.
- "Decret relatif aux poids et aux mesures du 18 germinal an 3 (7 avril 1795)" [Decree of 18 Germinal, year III (April 7, 1795) regarding weights and measures]. Grandes lois de la Republique (in French). Digithèque de materiaux juridiques et politiques, Universite de Perpignan. Archived from the original on 10 May 2013. Retrieved 3 November 2011.
- Convention nationale, decret du 1er août 1793, ed. Duvergier, Collection complète des lois, decrets, ordonnances, règlemens avis du Conseil d'etat, publiee sur les editions officielles du Louvre, vol. 6 (2nd ed. 1834), p. 70 Archived 2015-04-02 at the Wayback Machine. The metre (mètre) on which this definition depends was itself defined as the ten-millionth part of a quarter of Earth's meridian, given in traditional units as 3 pieds, 11.44 lignes (a ligne being the twelfth part of an pouce (inch), or the 140-4th part of a pied.
- Charlton T. Lewis, Charles Short, A Latin Dictionary s.v. "gramma" Archived 2015-07-17 at the Wayback Machine, 1879
- Knorr, Wilbur R. (1996). "Carmen de ponderibus et mensuris". In Hornblower, Simon; Spawforth, Antony (eds.). The Oxford Classical Dictionary (3rd ed.). Oxford: Oxford University Press. p. 292. ISBN 019866172X.
- Henry George Liddell. Robert Scott. A Greek-English Lexicon (revised and augmented edition, Oxford, 1940) s.v. γράμμα Archived 2015-07-17 at the Wayback Machine, citing the tenth-century work Geoponica and a fourth-century papyrus edited in L. Mitteis, Griechische Urkunden der Papyrussammlung zu Leipzig, vol. i (1906), 62 ii 27.
- Pat Chapman (2007). India Food and Cooking: The Ultimate Book on Indian Cuisine. London: New Holland Publishers (UK) Ltd. p. 64. ISBN 978-1845376192. Retrieved 20 November 2014.
Most of the world uses the metric system to weigh and measure. This book puts metric first, followed by imperial because the US uses it (with slight modifications which need not concern us).
- Gisslen, Wayne (2010). Professional Cooking, College Version. New York: Wiley. p. 107. ISBN 978-0-470-19752-3. Retrieved 20 April 2011.
The system of measurement used in the United States is complicated. Even when people have used the system all their lives, they still sometimes have trouble remembering things like how many fluid ounces are in a quart or how many feet are in a mile. ... The United States is the only major country that uses almost exclusively the complex system of measurement we have just described.
- "System of Measurement Units - Engineering and Technology History Wiki". ethw.org. Archived from the original on 29 April 2018. Retrieved 29 April 2018.
- "Circulating Coin Designs". Japan Mint. Archived from the original on 18 September 2009. Retrieved 7 March 2010.