Planck constant

Symbol h. The fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency. It has the value 6.626 0755(40) × 10⁻³⁴ J s. It is named after Max Planck. In quantum-mechanical calculations the rationalized Planck constant (or Dirac constant) ħ = h/2π = 1.054 589 × 10⁻³⁴ Js is frequently used.