# Proton Mass Constant

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

## protonMass

Proton mass

Try it yourself:

```calculio
protonMass
```

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## Proton mass: mass of a nucleon

**protonMass** is the rest mass of a proton, commonly used in atomic, nuclear, and particle calculations. It is close to, but not equal to, the [neutronMass](https://calcul.io/constants/neutronMass/index.md) and far larger than the [electronMass](https://calcul.io/constants/electronMass/index.md).

## Use and caveats

Use it in SI mass calculations or convert through [speedOfLight](https://calcul.io/constants/speedOfLight/index.md) for rest energy. Atomic mass includes binding effects, so do not replace it blindly with [atomicMass](https://calcul.io/constants/atomicMass/index.md).

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