Force on Solenoid Plunger

Kalagaraz

I'm trying to figure out how to calculate the actual physical force on a solenoid plunger. I.E what kind of load it can pull or push.

So if I setup a magnetic circuit and calculate the flux going through it at maximum airgap, am I right to assume that the force is equal (B^2 * A) / (2*u) where B is the flux density at end of plunger, A is the cross sectional area at end of plunger, and u is the magnetic permeability of a vacuum? Obviously force would increase as the air gap closes, but I really only need to know worst case scenario and best case scenario (no air gap).

B would be the flux divided by cross sectional area at end of plunger?

Thanks.