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Short description: Metric unit of mass
Gram (pen cap on scale).jpg
The mass of this pen cap is about 1 gram. A weight scale such as this can give an accurate reading of mass for many objects (see Weight vs. mass).
General information
Unit systemUCUM base unit and CGS unit
Unit ofMass
1 g in ...... is equal to ...
   SI base units   10−3 kilograms
   CGS units   1 gram
   Imperial units
U.S. customary
   0.0353 ounces

The gram (originally gramme;[1] SI unit symbol g) is a unit of mass in the metric system.

Originally defined as of 1795 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",[2] the defining temperature (~0 °C) was later changed to 4 °C, the temperature of maximum density of water.

However, by the late 19th century, there was an effort to make the base unit the kilogram and the gram a derived unit. In 1960, the new International System of Units defined a gram as one thousandth of a kilogram (i.e., one gram is 1×10−3 kg). The kilogram, as of 2019, is defined by the International Bureau of Weights and Measures from the fixed numerical value of the Planck constant (h), which is 6.62607015×10−34 kg⋅m2⋅s−1.[3][4]

Official SI symbol

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),[5]: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.[6][7]

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),[8] 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.[lower-alpha 1] There is also evidence that the Greek γράμμα was used in the same sense at around the same time, in the 4th century, and survived in this sense into Medieval Greek,[10] while the Latin term did not remain current in Medieval Latin and was recovered in Renaissance scholarship.[lower-alpha 2]

The gram was the fundamental unit of mass in the 19th-century centimetre–gram–second system of units (CGS). The CGS system co-existed with the meter-kilogramme-second system of units (MKS), 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.


The gram is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide.[11][12] Liquid ingredients may be measured by volume rather than mass.

Many 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.

Conversion factors

  • 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) = 8.98755179×1013 joules (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) [13]
  • 500 grams (g) = 1 Jin in the Chinese units of measurement.


  • 1 gram is roughly equal to 1 small paper clip or pen cap.
  • The Japanese 1 yen coin has a mass of 1 gram,[14] lighter than the British penny (3.56 g), the United States penny (2.5 g), the Euro cent (2.30 g), and the Australian 5 cent coin (2.80 g).

See also


  1. 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.[9] 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, Décret 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.
  2. In the Renaissance, the carmen de ponderibus et mensuris was received as a work of the 1st-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


  1. "Weights and Measures Act 1985 (c. 72)". The UK Statute Law Database. Office of Public Sector Information. "§92." 
  2. "Décret relatif aux poids et aux mesures" (in fr). 1795. 
  3. Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018),, retrieved 17 May 2020 
  4. Decision CIPM/105-13 (October 2016). The day is the 144th anniversary of the Metre Convention.
  5. 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.
  6. "Décret relatif aux poids et aux mesures du 18 germinal an 3 (7 avril 1795)" (in fr). Grandes lois de la République. Digithèque de matériaux juridiques et politiques, Université de Perpignan. 
  7. Convention nationale, décret du 1er août 1793, ed. Duvergier, Collection complète des lois, décrets, ordonnances, règlemens avis du Conseil d'état, publiée sur les éditions officielles du Louvre, vol. 6 (2nd ed. 1834), p. 70 . 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 12th part of an pouce (inch), or the 144th part of a pied.
  8. Charlton T. Lewis, Charles Short, A Latin Dictionary s.v. "gramma" , 1879
  9. Knorr, Wilbur R. (1996). "Carmen de ponderibus et mensuris". in Hornblower, Simon; Spawforth, Antony. The Oxford Classical Dictionary. (3rd ed.). Oxford: Oxford University Press. p. 292. ISBN 019866172X. 
  10. Henry George Liddell. Robert Scott. A Greek-English Lexicon (revised and augmented edition, Oxford, 1940) s.v. γράμμα , citing the 10th-century work Geoponica and a 4th-century papyrus edited in L. Mitteis, Griechische Urkunden der Papyrussammlung zu Leipzig, vol. i (1906), 62 ii 27.
  11. 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 2014-11-20. "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)." 
  12. Gisslen, Wayne (2010). Professional Cooking, College Version. New York: Wiley. p. 107. ISBN 978-0-470-19752-3. Retrieved 2011-04-20. "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." 
  13. "System of Measurement Units - Engineering and Technology History Wiki". 
  14. "Circulating Coin Designs". Japan Mint.