What is the Planck constant?
The Planck constant is h = 6.62607015e-34 J·s, exact by SI definition (zero uncertainty). In eV·s it is 4.135667696e-15 eV·s.
Open the interactive PhysRef tool →Key facts
| Value | 6.62607015e-34 J·s |
|---|---|
| Symbol | h |
| In eV·s | 4.135667696e-15 eV·s |
| Exactness | Exact by SI definition (uncertainty 0) |
| Source | CODATA 2018 |
Frequently asked questions
What is the value of Planck's constant?
h = 6.62607015e-34 joule-seconds, an exact defining constant of the SI since the 2019 redefinition of the kilogram.
What does the Planck constant represent?
It relates a photon's energy to its frequency via E = h·f, setting the quantum of action in physics.
Is the Planck constant exact?
Yes, it is fixed exactly at 6.62607015e-34 J·s and now defines the kilogram.
Related pages
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