Planck constant

The Planck constant (h) is 6.62607015 × 10^-34 m² kg/s (m²kg/s is equivalent to joules × seconds). This value is exact by design: the International System of Units (SI) now defines the relevant units based upon this and other physical constants. The relation (Planck relation) of a photon's energy (E) to its frequency (f) is:

E = h × f

The constant and the Planck function were conceived by Max Planck as a mathematical means to describe the black-body spectrum. The reduced Planck constant (aka Dirac constant, abbreviated ℏ) is h / 2π, which is convenient because many equations incorporate this expression.