Definition of the mole

Corresponding Author: Jürgen Stohner

In 2011 the General Conference on Weights and Measures (CGPM) noted the intention of the International Committee of Weights and Measures (CIPM) to revise the entire International System of Units (SI) by linking all seven base units to seven fundamental physical constants. Of particular interest to chemists, new definitions for the kilogram and the mole have been proposed. A recent IUPAC Technical Report* discussed these new definitions in relation to immediate consequences for the chemical community. This IUPAC Recommendation on the preferred definition of the mole follows from this Technical Report. It supports a definition of the mole based on a specified number of elementary entities in contrast to the present 1971 definition.

*Marquardt, R., J. Meija, Z. Mester, M. Towns, R. Weir, R. Davis, and J. Stohner (2017): “A critical review of the proposed definitions of fundamental chemical quantities and their impact on chemical communities (IUPAC Technical Report),” Pure Appl. Chem., AOP published online 13 June 2017,

Public review ended 30 June 2017

IUPAC Recommendations published in PAC Jan 2018

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