When subjected to a magnetic induction B, an elementary volume v of magnetizable substance acquires local magnetization M, where M is the magnetic moment of the elementary volume.

The volumetric intensity of magnetization per unit volume is:

The dimensions of the magnetic moment are:

Electrical intensity × surface = I.m2

? is the magnetic susceptibility, which is approximately 10-5 in the SI.

As [ M ] = I.m 2 , we have [ M/v ] = I.m?1

J is therefore measured in the same units as H, and the magnetic susceptibility is a dimensionless number.