Hi and welcome. Remember that the seam takes up room when you sew your patches together. So as Lakekids said, figure out the size of one grid square of your graph paper, calculate the size of each patch, then add a quarter of an inch to all 4 sides. So for instance if you decide that a patch is a 4" square, you would cut the piece 4 1/2" to allow for the seam allowance.