effective from 20 May 2019, the International System of Units, the SI, is the system of units in which:
the unperturbed ground state hyperfine transition frequency of the caesium 133 atom,
Cs, is 9 192 631 770 Hz,the speed of light in vacuum, c, is 299 792 458 m/s,
the Planck constant, h, is 6.626 070 15 × 10^–34 J s,
the elementary charge, e, is 1.602 176 634 × 10^–19 C,
the Boltzmann constant, k, is 1.380 649 × 10^–23 J/K,
the Avogadro constant, NA, is 6.022 140 76 × 10^23 mol–1.
the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, is 683 lm/W,
where the hertz, joule, coulomb, lumen, and watt, with unit symbols Hz, J, C, lm, and W, respectively, are related to the units second, metre, kilogram, ampere, kelvin, mole, and candela, with unit symbols s, m, kg, A, K, mol, and cd, respectively, according to
Hz = s^–1,
J = kg m^2 s^–2,
C = A s,
lm = cd m^2 m^–2 = cd sr, (sr = esterradiano a unidade de ângulo sólido)
and
W = kg m^2 s^–3
And god make the Earth in six days and rested in the seventh. :-)
