I always trim using the center "cross hair" seams as my quide. I know that if I want a 5 inch FINISHED square I have to trim it to 5 1/2 so from center to one side is going to be 2 3/4inches so I line the center vert. and horiz. lines up with 2 3/4 and then trim two sides (top and side). turn and do the same thing for the other two sides and I end up with a 5 1/2 inch square.