Wing loading is highly over-rated. Wing loading by itself gives absolutely ZERO indication of how a plane will fly. The ONLY way wing loading can give a useful comparison is if you compare two exactly identical planes in every respect, except they weigh different amounts.

I'm not sure I understand the question of the original post, but if one wants to calculate wing loading becasue they need math practice, the first response by LouW was correct, weight into area.

Any statement like you must have a wing loading of X to fly good is uninformed. Montauge had a good go at it. While caluclating "wing loading" is straight forward, calculating how "light" or "heavy" a plane will "feel" in the air is considerably more complicated.

I am guilty of throwing out the cubic loading calc on ocassion. We don't live in a linear world. While not perfect, cubic wing loading (weight into volume of wing) tells a lot more about the aerodynamics of a plane than just wing loading. True, change scale dramatially or airfoils, etc., and it all goes out the window. Sigrun's link explains this in more detail.

By "good flying plane", what we really mean is that the plane falls into a certain lift/drag range with a wing that generates X lift at Y angle of attack where the Y angle is in some acceptable range for a given flight speed Z at an airdensity of A and of course X must equal the weight of the plane.

It really comes down to full blown aerodynamic theory with lift/drag ratios, flows, Renyolds #, etc. In short, there is no cheat, rule of thumb, seat of the pants estimate, or easy way to quantify aircraft performance. With enough experience, one can guess fairly closely how a plane will fly, but to actually quantify this you really need to crank all the formulas and do tunnel testing.

Cheers