The NIST Reference on Constants, Units and Uncertainty

Fundamental Physical Constants


Units &
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International aspects of establishing recommended values
Role of CODATA

    This site provides access to the current (2022) set of self-consistent values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use.

    CODATA was established in 1966 as an interdisciplinary committee of the International Council of Science (ICSU), formerly the International Council of Scientific Unions. It seeks to improve the compilation, critical evaluation, storage, and retrieval of data of importance to science and technology. The CODATA Task Group on Fundamental Constants was established in 1969. Its purpose is to periodically provide the international scientific and technological communities with an internationally accepted set of values of the fundamental physical constants and closely related conversion factors for use worldwide. The first such CODATA set was dated 1973, the second 1986, the third 1998, the fourth 2002, the fifth 2006, the sixth 2010, the seventh (2014), the eighth 2018, and the ninth (the current set) 2022.

    In view of the modern and highly beneficial trend towards making new information immediately and widely available on the Internet, especially via the World Wide Web, the CODATA Task Group on Fundamental Constants altered its approach to the compilation of the values of the constants. More specifically, it took advantage of the high degree of computerization that was incorporated into the 1998 CODATA compilation to provide a new set of CODATA recommended values every four years.

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related to the constants.