What is the reduced Planck constant (ħ)?
The reduced Planck constant is ħ = h/2π = 1.054571817e-34 J·s, exact by SI definition. In eV·s it is 6.582119569e-16 eV·s.
Open the interactive PhysRef tool →Key facts
| Value | 1.054571817e-34 J·s |
|---|---|
| Symbol | ħ (h-bar) |
| In eV·s | 6.582119569e-16 eV·s |
| Relation | ħ = h / 2π |
| Source | CODATA 2018 |
Frequently asked questions
What is h-bar equal to?
ħ = 1.054571817e-34 J·s, which is the Planck constant h divided by 2π.
Where is ħ used?
It appears throughout quantum mechanics, e.g. in the Heisenberg uncertainty principle and the Schrodinger equation.
Is ħ exact?
Yes, because h is exact; ħ = h/2π is therefore exact to the precision of π.
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