The Planck constant, h, is a fundamental physical constant. Electromagnetic radiation has a dual nature. It can be considered to be composed of waves or of particles ( photons). The wavelike and particle-like properties are related by Planck's Law in which the constant of proportionality is h. (h = 6.62 x 10-34 Joule seconds).

the numerical factor h relating the frequency v of a photon to its energy e in the expression e = hn. the Planck constant has the value h = 6.62620 x 10-27 erg sec.

The fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency. (Course Material/Radiography/Physics/comptonscattering.htm)

6.6260755e-34 ± 4.0e-40 J s