Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.

Updated July 24, 2017

Planck's Constant Definition: Planck's constant is the proportionality constant relating a photon'senergy to its frequency.

Planck's constant is expressed by the symbol h

h = 6.62606896(33) x 10^{-34} J·sec h = 4.13566733(10) x 10^{−15} eV·sec