Originally Posted by raptureready
It's because you're going to end up making half square triangles that will end up being 3 1/2". Since you always have to trim them up anyway, it's much easier just to cut 4" squares, mark a diagonal line on the back, put the two you need faces together and sew 1/4" on both sides of your line. Then just cut on your line, press them open and trim to 3 1/2" square.
I just read in a book called "Stash and Splash" that if you cut the square 4 inches and use a regular presser foot to sew on both sides of the diagonal line, you will have a 31/2 square without having to cut down to size. On almost all sewing machines the presser foot measures 3/8 inch from needle to edge of the foot so you are making a larger seam to compensate for the larger square. How about that! Rita