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The gram (originally gramme; SI unit symbol g) is a Physical unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.
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 Cubic centimetre], and at the temperature of Melting point ice", the defining temperature (≈0 °C) was later changed to 4 °C, the temperature of maximum density of water.
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 one-thousandth of a kilogram (i.e., one gram is ). The kilogram, as of 2019, is defined by the International Bureau of Weights and Measures from the fixed numerical value of the Planck constant (). Decision CIPM/105-13 (October 2016) . The day is the 144th anniversary of the Metre Convention.
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.
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),Charlton T. Lewis, Charles Short, A Latin Dictionary s.v. "gramma" , 1879 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. 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,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. while the Latin term died out in Medieval Latin and was recovered in Renaissance scholarship.
The gram was the base unit of mass in the 19th-century centimetre–gram–second system of units (CGS). The CGS system coexisted with the metre–kilogram–second system of units (MKS), first proposed in 1901, during much of the 20th century, but the gram was displaced by the kilogram as the base unit for mass when the MKS system was chosen for the SI base units in 1960.
Many standards and legal requirements for 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.
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