Title: amount of substance
Long Title: IUPAC Gold Book - amount of substance
DOI: 10.1351/goldbook.A00297
Status: current
Index: quantity

Definition
The amount of substance, symbol \(n\), of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

Note
This wording is part of the definition of the SI base unit mole, which was agreed upon by the 26th CGPM in November 2018 with effect from 20 May 2019.

Sources
- BIPM, Le Système international d’unités (SI), SI Brochure, 9e ed. (2019), p. 21 (https://www.bipm.org/fr/publications/si-brochure/)
- BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 134 (https://www.bipm.org/en/publications/si-brochure/)
- PAC, 2018, 90, 175. 'Definition of the mole' on page 177 (https://doi.org/10.1515/pac-2017-0106)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00297/html
- json: https://goldbook.iupac.org/terms/view/A00297/json
- xml: https://goldbook.iupac.org/terms/view/A00297/xml

Citation: Citation: 'amount of substance' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.A00297
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Accessed: 2026-04-19T00:14:36+00:00