Sigrun,
Actually, you missed the entire point. The question isn't "how do you calculate wing loading". The question is "how high can wing loading be and still fly ok".

No one has said anything that would say you calculate the conventional wingloading anyway other than what you've said.

However, I can say with absolute certainly that a wingloading of 30oz/sqft as quoted by chrischicago-RCU above might be ok for a large model, but if I tried to fly my .15 powered combat ships like that, I'd never get them off the ground. (I shoot for around 10, 12 tops, anything more doesn't fly well at that scale).

So, it's clear to anyone who has flown more than one size of model that wingloading by itself is a totally useless number. It tells you absolutely nothing about how a plane will fly. You MUST know how big the plane is to go along with that wingloading.

The various cubic forumulas (and there are several of them) all try to add a scaling factor, usually based on wing span, to adjust the wingloading for differnet sized models. And, as long as you are talking about simular types of models with simular airfoils, they do work pretty well.

However, even those cubic forumlas break down when you compare a Cub to an Extra for example.

In other words, how a plane flys at a given wing loading is determined by "a number of factors", such as the airfoil, CG, thrust, Renylds number, etc.

And that is what was being pointed out above. That there are a number of factors that determine the performace of an airplane, and the wingloading is only useful in the context of those other factors.