Weight estimations at this point are just educated guesses. Experience plays a big role in weight estimations since it is hard to weight a structure that hasn't been build or even worked out. All we know at this point are dimensions so I use a value per inch to help calculate total airframe weight. For my propjets, I use a value of .36oz/inch. Where did this number come from? It's just a rough estimate taken from other models I've built in the past. So for example, if my fuselage is 60 inches long, I would multiply 60 by .36oz and get 21.6oz. You can also do the same for the wing along it span. The weight calculation is not perfect but it will get you going for now. Now to figure out about how much your model will weight, just add the estimations for the fuselage and wing with all the other components you plan to use like engine, servos, battery, etc. You should now have your estimated weight and now you can figure out the wing loading.
Wing loading will give you an idea about how well your model will fly. Take your value for wing area and convert it to square feet. Now, divide the weight (in oz) by the area (in sq ft). For example, my U-2 weighs about 7lbs and has a wing area of about 800 sq inches. I first convert the sq in to sq ft and get 5.555 sq ft (800 divided by 144). Now convert lbs to oz (7 multiplied by 16) which gives me 112oz. Next divide 112 oz by 5.555 sq ft. I get 20.16 oz/ sq ft as a figure. This is my wing loading. To make this easier I created a wing loading chart.
