- e is the elementary charge,
- ħ is the reduced Planck constant,
- mp is the proton rest mass, and
- c is the speed of light
In SI units, its value is approximately:
The nuclear magneton is the natural unit for expressing magnetic dipole moments of heavy particles such as nucleons and atomic nuclei. On the contrary, the dipole moment of the electron, which is much higher as a consequence of much higher charge-to-mass ratio, is usually expressed in corresponding units of the Bohr magneton.