By my figuring if you cut your squares at 4 ¾" and sew ¼" seams you should end up with a 12 ¾" finished block. If you cut your squares at 4 5/8" inch your finished block would be 12 3/8" soooooo..... if you had a ruler with the 1/16" markings maybe you could try cutting your squares at 4 and 11/16ths OR.... how about just cutting them at the 4 ¾" and then trim down the block from 12 ¾ to 12 ½" ?