Title: atomic mass constant
Long Title: IUPAC Gold Book - atomic mass constant
DOI: 10.1351/goldbook.A00497
Status: current
Index: constant

Definition
One twelfth of the mass of a carbon-12 atom in its nuclear and electronic ground state, \(m_{\rm{u}} = \pu{1.6605402(10)E-27 kg}\). It is equal to the unified atomic mass unit.

Related Terms
- ground state: https://goldbook.iupac.org//terms/view/G02704
- unified atomic mass unit: https://goldbook.iupac.org//terms/view/U06554

Sources
- CODATA Bull. 1986, 63, 1 (https://doi.org/10.6028/jres.092.010)
- PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 962 (https://doi.org/10.1351/pac199668040957)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00497/html
- json: https://goldbook.iupac.org/terms/view/A00497/json
- xml: https://goldbook.iupac.org/terms/view/A00497/xml

Citation: Citation: 'atomic mass constant' 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.A00497
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Accessed: 2026-04-20T12:43:05+00:00