# Planck Constant Constant

Use Planck Constant in Calcul.io. See what this built-in constant represents, enter it in an editable calculation, and review related values and units.

## planckConstant

Planck constant

Try it yourself:

```calculio
planckConstant
```

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## Planck constant: the quantum of action

**planckConstant**, h, relates a photon’s energy to its frequency through E = hν. Its SI unit is joule second, and its exact defined value underpins the modern SI kilogram.

## Practical use

Use h to convert frequency into photon energy, often together with [speedOfLight](https://calcul.io/constants/speedOfLight/index.md) for wavelength calculations. [reducedPlanckConstant](https://calcul.io/constants/reducedPlanckConstant/index.md) is h divided by 2π and is common in angular-frequency formulas.

## Caveats

Distinguish frequency ν from angular frequency ω; the latter normally uses reduced Planck constant. Use [multiply](https://calcul.io/function/multiply/index.md) for unit-consistent products and [elementaryCharge](https://calcul.io/constants/elementaryCharge/index.md) when converting energy in joules to electron-volts.

[All constants](https://calcul.io/constants/index.md)