I've made a quilt this way, can't remember the size of blocks. But the two squares that you sew together, then cut in half, need to be bigger than the 4 inch square--you're going to lose two seams, so I can't remember that exact figure, if a seam is 1/4", your squares need to be 4 1/2". Make one out of some scraps to be sure. Have fun and good luck!