RC plane designing

Hello,

I am interested in designing my own RC plane. For that I am looking for some calculations. I know there are some calculations like, if wingspan is this much than we can have a fuselage length of some 80% of wingspan or something like that.

I want that calculation so that, based on that formula I can design mine.

Can anyone please help me by sharing that calculation?

Thank you in advance,

You can try similar dimensions like this