I want to calculate the force between two magnets. In a previous Phys.SE question, I was told that I needed to use the dipole-dipole interaction, but that equation depends on $m$, the magnetic dipole moment of the magnet.
How do I calculate $m$? I found a source that said $m = p \ell$ where $p$ is the "magnetic pole strength" and $\ell$ is the length of the magnet, but I haven't found anything that says how to compute $p$.