i've made a quilt for my sister that is 60 wide x 71 long and i would like to do the backing in 12 inch squares with the 2 fabrics i've used for the front. I'm not doing the math correct because In my calculations i get 60 squares. Now Math never was my best subject but this can't be right. Would someone please help me with the CORRECT calculations. I thank you and my brain and hair thank you(because not much hair is left i'm pulling in out)

God Bless

Loretta