Hi neferkamichael,
It is a very valid question. As Pommie has pointed out, the total
flux density is a measurement of the number of field lines in any given cm2 of pole area. When plotting lines of
flux from a magnet of any shape, the closer the lines are together, the stronger the field will be.
The flux density depends on the grade of magnet and the relationship between the diameter and the
magnetic length (L/d ratio).
Magnets with larger pole areas relative to smaller lengths, have the lowest flux densities.
Magnets with smaller pole areas relative to longer magnetic lengths, have much higher flux densities.
It must also be consider that the flux density must be multiplied by the pole area to give the total magnetism, as flux density is only half of the equation when considering overall magnetic force.
We have put together a spreadsheet which may help with calculations relating to cylindrical and rectangular magnets. Unfortunately the forum is not letting me attach it. If anyone knows how to attach it then I will happily post it.