μ_B
Bohr magneton
The Bohr magneton is the natural unit of electron magnetic moment, defined as the reduced Planck constant times the elementary charge divided by twice the electron mass. Its value of 9.2740100657e-24 joules per tesla is a measured quantity, not an exact one, because the electron mass is still determined experimentally even though the Planck constant and the elementary charge are now fixed. The listed digits follow the current CODATA adjustment and carry a relative uncertainty of about three parts in ten billion.
Watch out: The electron's own magnetic moment is not exactly one Bohr magneton but about 1.00116 of one, the anomalous magnetic moment. That small excess is one of the most precisely tested predictions in all of physics.
| 1 μ_B | 9.2740101e-24 J/T |