Title: kilogram
Long Title: IUPAC Gold Book - kilogram
DOI: 10.1351/goldbook.K03391
Status: current
Index: unit

Definition
The kilogram, symbol \(\pu{kg}\), is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant \(h\) to be \(\pu{6.62607015E-34}\) when expressed in the unit \(\pu{J s}\), which is equal to \(\pu{kg m2 s-1}\), where the metre and the second are defined in terms of c and ΔνCs.

Related Terms
- Planck constant: https://goldbook.iupac.org//terms/view/P04685
- Δ<em>ν</em><sub>Cs</sub>: https://goldbook.iupac.org//terms/view/S05854

Source
- BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 131 (https://www.bipm.org/en/publications/si-brochure/)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/K03391/html
- json: https://goldbook.iupac.org/terms/view/K03391/json
- xml: https://goldbook.iupac.org/terms/view/K03391/xml

Citation: Citation: 'kilogram' 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.K03391
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Accessed: 2026-06-12T07:24:54+00:00