Lovely, I always had a hard time with this square. I learned that the middle square is 3" but to make the two half squares you need to make them 3 and a half. You need to use a quarter inch marker so you sew two lines. Then cut down the center. Now when you press you should have a quarter inch of material to see your diamond when you sew. It does make a difference when you sew that you sew a quarter inch and be your careful when you iron. I made all these mistakes. I hope this helps Karen Lynn from Freedom Ohio