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 °C, the temperature of maximum density of water). However, in a reversal of reference and defined units, a gram is now defined as one one-thousandth of the SI base unit, the kilogram, or 1×10-3 kg, which itself is now defined, not in terms of grams, but as being equal to the mass of a physical prototype of a specific alloy kept locked up and preserved by the International Bureau of Weights and Measures.
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),: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 (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 was used in the same sense at around the same time, in the 4th 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 is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide.
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.
^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, 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.
^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
^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. 70Archived 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 12th part of an pouce (inch), or the 144th part of a pied.
^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. ISBN019866172X.
^Henry George Liddell. Robert Scott. A Greek-English Lexicon (revised and augmented edition, Oxford, 1940) s.v. Archived 2015-07-17 at the Wayback Machine., 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.