1.1. Fundamental constants

The table below lists relevant fundamental constants (based on the 2018 CODATA recommended values). Digits in parentheses indicate uncertainty, relative to the last digit. For example, $7.85(1)$ indicates $7.85\pm 0.01$, and $1.3454(12)$ indicates $1.3454\pm 0.0012$.

Several of the constants have zero uncertainty, since they are defined as exact values. (The SI base units kg, m, C, K, and mol are defined through these constants.)

Symbol	Name	Value
$h$	Planck constant	$6.62607015\times {10}^{-34}\mathrm{J}\mathrm{s}$ (exact)
$\hslash$	reduced Planck constant	$1.054571817...\times {10}^{-34}\mathrm{J}\mathrm{s}$ (exact)
$c$	speed of light in vacuum	$299792458\mathrm{m}{\mathrm{s}}^{-1}$ (exact)
$e$	elementary charge	$1.602176634\times {10}^{-19}\mathrm{C}$ (exact)
$N_{\mathrm{A}}$	Avogadro constant	$6.02214076\times {10}^{23}{\mathrm{mol}}^{-1}$ (exact)
$k_{\mathrm{B}}$	Boltzmann constant	$1.380649\times {10}^{-23}\mathrm{J}{\mathrm{K}}^{-1}$ (exact)
$u$	atomic mass unit	$1.66053906660(50)\times {10}^{-27}\mathrm{kg}$
$m_{\mathrm{e}}$	electron mass	$9.1093837015(28)\times {10}^{-31}\mathrm{kg}$
$m_{\mathrm{p}}$	proton mass	$1.67262192369(51)\times {10}^{-27}\mathrm{kg}$
$m_{\mathrm{n}}$	neutron mass	$1.67492749804(95)\times {10}^{-27}\mathrm{kg}$
$a_0$	Bohr radius	$5.29177210903(80)\times {10}^{-11}\mathrm{m}$
$R_{\mathrm{\infty }}$	Rydberg constant	$10973731.568160(21){\mathrm{m}}^{-1}$
${ϵ}_0$	electric constant	$8.8541878128(13)\times {10}^{-12}{\mathrm{C}}^2{\mathrm{J}}^{-1}{\mathrm{m}}^{-1}$
${\mu }_{\mathrm{B}}$	Bohr magneton	$9.2740100783(28)\times {10}^{-24}\mathrm{J}{\mathrm{T}}^{-1}$
${\mu }_{\mathrm{N}}$	nuclear magneton	$5.0507837461(15)\times {10}^{-27}\mathrm{J}{\mathrm{T}}^{-1}$