What size box of fondant would I need to buy to cover a 10x2" square cake? Would one box that covers an 8" or 9" round work? Thanks!

According to the Wilton fondant chart it'd take 48 ozs. of fondant to cover a 10" x 4" square cake. If you have a 2" high cake you may need about 40 oz. in my estimation, so you'd have to buy 2 24oz. size boxes of Wilton fondant (if that is what you are going to be using).