I am math challenged so I use paper the length of the side, (plus the amount on the bottom and top) and fold the paper in half, then quarters etc. This gives me a crease for spacing my circle on the paper(plate with painter's tape across the middle). Once I have the outer curves where I want them' I reverse the plate for the inner curve. Once my paper pattern is perfect, I cut out the edge and pin it on the quilt. I do the other sides the same way and then stitch the curves before cutting the sandwich.