Building balsa wood aircraft models?

I didn't know were to ask this but this section seems appropriate, anyway I want to start getting into building model planes and power them using electric(I have nitro powered models and are very messy). But thing is I never built a model before so could u guys tell me how do I calculate scales like 1:32 and 1:18? The model kit is of a supermarine spitfire and it comes in either 1:32 or 1:18 but I dont know which is bigger and what wingspan it will be?