Section: 1 | CODATA Recommended Values of the Fundamental Physical Constants: 2018 |
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John R. Rumble, ed., CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), CRC Press/Taylor & Francis, Boca Raton, FL.
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Eite Tiesinga, Peter J. Mohr, David B. Newell, and Barry N. Taylor

This report gives the 2018 self-consistent set of values of the constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA). These values are based on a least-squares adjustment that take into account all data available up to December 31, 2018. They also reflect the major changes to the SI units made in 2019. See the International System of Units (SI) in this section for further details about these changes.

The tables below are extracted from reports (Refs. 1-4) prepared by the authors under the auspices of the CODATA Task Group on Fundamental Constants and the International Bureau of Weights and Measures (BIPM). The present members of the task group are:


  1. Mohr, P. J., Newell, D. B., and Taylor, B. N., J. Phys. Chem. Ref. Data 45, 043102, 2016. []
  2. Mohr, P. J., Newell, D. B., and Taylor, B. N., Rev. Mod. Phys. 88, 035009, 2016. []
  3. Available on the Web at <>.
  4. Newell, D. B., and Tiesinga, E., The International System of Units (SI), NIST Special Publication 330, 2019 Edition, National Institute of Standards and Technology, Gaithersburg, MD, 2019. []

The 2018 set of CODATA recommended values of the fundamental physical constants is based on the recently adopted definitions of the SI units as derived from a set of seven defining constants, as shown in Table 1. 

TABLE 1. The Seven Defining Constants of the SI and the Seven Corresponding Units They Define (Note: All constants are exact)

Defining constantSymbolNumerical valueUnit
hyperfine transition of cesium (113Cs)ΔνCs9 192 631 770Hz
speed of light in vacuumc, c0299 792 458m s-1
Planck constanth6.626 070 15 × 10-34J s
elementary chargee1.602 176 634 × 10-19C
Boltzmann constantk1.380 649 × 10-23J K-1
Avogadro constantNA6.022 140 76 × 1023mol-1
luminous efficacyKcd683lm W-1

Table 2 is an abbreviated list of the CODATA recomended values of the fundamental constants of physics and chemistry, based on the 2018 adjustment and the recently adopted defining SI constants and units (Table 1). Uncertainties are given when appropriate. See References 3 and 4 for additional information.

TABLE 2. Frequently Used Fundamental Constants of Physics and Chemistry Based on the 2018 CODATA Adjustment

QuantitySymbolNumerical valueUnitUncertainty
Continued on next page...
electron volt (e/C) JeV1.602 176 634 × 10-19Jexact
Josephson constant 2e/hKJ483 597.848 4... × 109Hz V-1exact
von Klitzing constant 2πh/e2RK25 812 807 45...Ωexact
molar gas constantR8.314 462 618...J mol-1 K-1exact
Stefan-Boltzmann constant (π2/60)k4/ℏ3c2σ5.670 374 419... × 10-8W m-2 K-4exact
(unified) atomic mass unit (1/12)m(12C)u1.660 539 066 60 × 10-27kg0.000 000 000 50 × 10-27
Newtonian constant of gravitationG6.674 30⁢ × 10-11m3 kg-1 s-20.000 15 × 10-11
fine-structure constant  e2/4πϵ0c α7.297 352 5693 × 10-30.000 000 0011 × 10-3
inverse fine-structure constantα-1137.035 999 084⁢0.000 000 021
Rydberg constant α2mec/2⁢hR10 973 731.568 160m-10.000 021
vac. magnetic permeability 4παℏ/(e2c)μ01.256 637 062 12 × 10-6N A-20.000 000 000 19 × 10-6
electron massme9.109 383 7015 × 10-31kg0.000 000 0028 × 10-31
proton massmp1.672 621 923 69 × 10-27kg0.000 000 000 51 × 10-27
proton-electron mass ratiomp/me1836.152 673 430.000 000 11
reduced Compton wavelength ℏ/(mec)C3.861 592 6796 × 10-13m0.000 000 0012 × 10-13
Bohr radius /(αmec)α05.291 772 109 03 × 10-11m0.000 000 000 80 × 10-11
Bohr magneton e/(2me)μB9.274 010 0783 × 10-24J T-10.000 000 0028 × 10-24
h/2⁢π1.054 571 817... × 10-34J sexact
vac. electric permittivity 1/(μ0c2)ϵ08.854 187 8128 × 10-12F m-10.000 000 0013 × 10-12

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