Term: Avogadro constant, NA, L https://doi.org/10.1351/goldbook.A00543 Definition: The Avogadro constant, NA = 6.022 140 76 x 1023 mol-1, is a proportionality constant between the quantity amount of substance (n, with unit mole) and the quantity for counting entities (N with unit one, symbol 1), N = NAn. Notes: 0) In the revision of the International System of Units (SI) of 2019 the Avogadro constant became one of the seven defining constants with the exact value 6.022 140 76 x 1023 mol-1. 1) The Avogadro number is the exact numerical value of the Avogadro constant, 6.022 140 76 x 1023 2) While the symbol NA is used to honour Amedeo Avogadro, the symbol L is used in honour of Josef Loschmidt. Related Terms: 1) entities (http://doi.org/10.1351/goldbook.N04266). 2) amount of substance (http://doi.org/10.1351/goldbook.A00297). Source: BIPM, Le Système international d’unités (SI), SI Brochure, 9e ed. (2019), p. 17 (https://www.bipm.org/fr/publications/si-brochure/) Citation: 'Avogadro constant, <em>N</em><sub>A</sub>, <em>L</em>' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.A00543 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.