Are you going to quilt it or a LA will quilt. If I pin and quilt, I add 4"or5" to the size=50"x60". I don't like to waste fabric so I would do a horizontal seam cutting 50" in length. After pinning the quilt, I would remove the excess from the bottom of the quilt. If you are having someone quilt it for you, I would ask them on the amount to add to your quilt top.