Overview#

SI Defining Constants, have been Since 2019, the magnitudes of all SI Base Units have been defined by declaring that seven constants that have certain exact numerical values when expressed in terms of their SI Base Units or SI Derived Unit.

Symbol	Name	Exact value
ΔνCs	hyperfine transition frequency of Cs	9,192,631,770 Hz
c	speed of light	299,792,458 m/s
h	Planck constant	6.62607015×10−34 J⋅s
e	elementary charge	1.602176634×10−19 C
k	Boltzmann constant	1.380649×10−23 J/K
NA	Avogadro constant	6.02214076×1023 mol−1
Kcd	luminous efficacy of 540 THz radiation	683 lm/W!! More Information

There might be more information for this subject on one of the following:

• International System of Units