Funny, I am completely math challenge but I just 'have at it'& it all works out. I guess you would say that I am visual-spacial....or just "special" maybe :-) When I buy fabric I have no idea what I need, I just look at it & say whatever I think might work. Sometimes I have a little extra but that goes into my stash, sometimes I have a few orphan blocks but it beats thinking too hard. LOL!!!