I prefer to add an inch to the square, say 4 1/2" square, draw line corner to corner then stitch 1/4" both sides, cut on line, press, then square up to 3 1/2". I've been quilting for a long time and no matter how careful I am, I always need to square them up to 3 1/2" using the 45 degree angle on the ruler. My quilt blocks are so much more accurate using this method, although it involves a little extra work, but to me the results are well worth it.