Gram

gram
gram
	The mass of this Japanese one yen coin is 1.00 gram. A weight scale such as this can give an accurate reading of mass for many objects (see Weight vs. mass).
General information
Unit system	SI
Unit of	Mass
Symbol	g
Conversions
1 g in ...	... is equal to ...
SI base units	10−3 kilograms
Imperial units; U.S. customary	0.0352740 ounces
daltons	6.02214076×1023 Da

The gram (originally gramme;^[1] SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.

Originally defined in 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 the temperature of maximum density of water (approximately 4 °C). Subsequent redefinitions agree with this original definition to within 30 parts per million (0.003%), with the maximum density of water remaining very close to 1 g/cm³, as shown by modern measurements.^[3]

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 metre, the second, and from the fixed numerical value of the Planck constant ( $h$ ).^[4]^[5]

^ "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. §92.
^ "Décret relatif aux poids et aux mesures" (in French). 1795. Archived from the original on 25 February 2013.
^ The density of water is 0.999972 g/cm³ at 3.984 °C. See Franks, Felix (2012). The Physics and Physical Chemistry of Water. Springer. ISBN 978-1-4684-8334-5.
^ Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018) (PDF), archived from the original (PDF) on 29 April 2018, retrieved 17 May 2020
^ Decision CIPM/105-13 (October 2016) Archived 24 August 2017 at the Wayback Machine. The day is the 144th anniversary of the Metre Convention.

[1] "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. §92.

[2] "Décret relatif aux poids et aux mesures" (in French). 1795. Archived from the original on 25 February 2013.

[3] The density of water is 0.999972 g/cm³ at 3.984 °C. See Franks, Felix (2012). The Physics and Physical Chemistry of Water. Springer. ISBN 978-1-4684-8334-5.

[draft-resolution-A-4] Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018) (PDF), archived from the original (PDF) on 29 April 2018, retrieved 17 May 2020

[5] Decision CIPM/105-13 (October 2016) Archived 24 August 2017 at the Wayback Machine. The day is the 144th anniversary of the Metre Convention.

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