Amount of Substance (n) ○◂ Entries

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Amount of Substance (n) ○◂｜Definition｜1st｜20260107002856-00-⌔

Amount of substance - Wikipedia

Amount of substance

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In chemistry, the amount of substance (symbol n) in a given sample of matter is defined as a ratio (n = N/N${}_A$) between the number of elementary entities (N) and the Avogadro constant (N${}_A$). It is one of the seven base quantities of the International System of Units, SI. The unit of amount of substance in the SI is the mole (symbol: mol), a base unit.¹ Since 2019, the mole has been defined such that the value of the Avogadro constant N${}_A$ is exactly 6.022 140 76 × 10${}^{23}$ mol${}^{-1}$, defining a macroscopic unit convenient for use in laboratory-scale chemistry. The elementary entities are usually molecules, atoms, ions, or ion pairs of a specified kind. The particular substance sampled may be specified using a subscript or in parentheses, e.g., the amount of sodium chloride (NaCl) could be denoted as n${}_{NaCl}$ or n (NaCl). Sometimes, the amount of substance is referred to as the chemical amount or, informally, as the “number of moles” in a given sample of matter. The latter term is deprecated by the IUPAC because, for a substance X, the correct meaning of “number of moles” is n (X)/mol. The amount of substance in a sample can be calculated from measured quantities, such as mass or volume, given the molar mass of the substance or the molar volume of an ideal gas at a given temperature and pressure.

Printed 2026-06-28.

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Footnotes

1. The International System of Units (PDF), V4.01 (9th ed.), International Bureau of Weights and Measures, Jun 2026, ISBN 978-92-822-2272-0 p. 134 ↩

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