Ok, I've seen many proofs of this, all being the same, but the closest I could find online was here: http://freespace.virgin.net/mark.davidson3/IMS2121/buoyancy/Buoyancy.html Basically the idea is you mess around with the formulas for pressure and hey bingo. However, I have one question - the general idea seems that the up force is a reaction force due to the force downwards of the water above the cube + the weight of the cube, with would indeed be h2pgA IF the cube was of water! Otherwise, the density is not the same and therefore you would have to bring more variables into the proof. Do you get me? Can anyone help and elaborate on the proof? Thanks.