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CODATA Recommended Values of the Fundamental Physical Constants: 2018

TitleCODATA Recommended Values of the Fundamental Physical Constants: 2018
Publication TypeJournal Article
Year of Publication2021
AuthorsE. Tiesinga, P. J. Mohr, D. B. Newell, and B. N. Taylor
JournalJ. Phys. Chem. Ref. Data
Date PublishedSEP 1
Type of ArticleArticle
Keywordsconventional and SI electrical units, electron and muon g-factors, fine-structure constant, fundamental constants, precision measurements, proton radius, QED, revised SI, Rydberg constant

We report the 2018 self-consistent values of constants and conversion factors of physics and chemistry recommended by the Committee on Data of the International Science Council. The recommended values can also be found at The values are based on a least-squares adjustment that takes into account all theoretical and experimental data available through 31 December 2018. A discussion of the major improvements as well as inconsistencies within the data is given. The former include a decrease in the uncertainty of the dimensionless fine-structure constant and a nearly two orders of magnitude improvement of particle masses expressed in units of kg due to the transition to the revised International System of Units (SI) with an exact value for the Planck constant. Further, because the elementary charge, Boltzmann constant, and Avogadro constant also have exact values in the revised SI, many other constants are either exact or have significantly reduced uncertainties. Inconsistencies remain for the gravitational constant and the muon magnetic-moment anomaly. The proton charge radius puzzle has been partially resolved by improved measurements of hydrogen energy levels. (c) 2021 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved.