i'm going to guess that you could model a magnet as being made of units
   of magnetic-strength-with-mass and an electromagnet as being made of
   units of magnetic-strength-with-current and you'd basically want the
   smallest volume of the highest grade magnet, shape and distance
   unaddressed, to accelerate it with a given electromagnet. each magnet
   particle needing some number of electromagnet units to lift it.
   electromagnetic seem to be sold based on a raw force, such as "holding
   force" . unsure what this force represents. alternatively one could
   wrap cores with wire by hand.