Planck constant
= 6.626 070 15 × 10−34 J Hz−1
- Value
- 6.626 070 15 × 10−34 J Hz−1
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# Planck constant, CODATA 2022 (NIST)
h = 6.62607015e-34 # J Hz^-1, exact
# SciPy: scipy.constants.physical_constants['Planck constant']What it is
The quantum of action. It links the energy of a photon to its frequency, E = hν, and sets the scale at which quantum effects matter. Since 20 May 2019 its value is fixed exactly, and that fixed value defines the kilogram; Kibble balances and silicon-sphere experiments turn it into real masses.
This is one of the seven defining constants of the SI. Its value was measured until the CODATA 2017 special adjustment fixed it, and it has been exact since the new definitions took effect on 20 May 2019.
Equations
- photon energy
- de Broglie wavelength
- reduced Planck constant
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm2 g s−1) | 6.626 070 15 × 10−27 | exact |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display.
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 6.626 070 15 × 10−34 | exact | exact |
| 2018 | 6.626 070 15 × 10−34 | exact | +1.4 σ of 2014 |
| 2014 | 6.626 070 040(81) × 10−34 | 1.2 × 10−8 | +1.6 σ of 2010 |
| 2010 | 6.626 069 57(29) × 10−34 | 4.4 × 10−8 | +1.8 σ of 2006 |
| 2006 | 6.626 068 96(33) × 10−34 | 5.0 × 10−8 | −0.3 σ of 2002 |
| 2002 | 6.626 0693(11) × 10−34 | 1.7 × 10−7 | +1.0 σ of 1998 |
| 1998 | 6.626 068 76(52) × 10−34 | 7.8 × 10−8 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).