The Curie–Weiss law is an adapted version of Curie's law, which for a paramagnetic material may be written in SI units as follows, assuming :
Here μ is the permeability of free space;  M the magnetization (magnetic moment per unit volume),  is the magnetic field, and C the material-specific Curie constant:
where  is Boltzmann's constant,  the number of magnetic atoms (or molecules) per unit volume,  the Landé g-factor,  the Bohr magneton,   the angular momentum quantum number.
For the Curie-Weiss Law the total magnetic field is  where  is the Weiss molecular field constant and then
which can be rearranged to get
which is the Curie-Weiss Law
where the Curie temperature  is