It's not a square or even a rectangle!  It's a circle that measures approximately 13" which has been determined to be the best size for your suit pocket.  Because the fabric is cut partly on the bias, it gives the pocket round some body, a characteristic that is lacking on regular pocket squares, particularly with cotton and linen fabrics.  Various color styles available --- please advise on colored piping (i.e., RED, PINK, WHITE, LIGHT BLUE or BLUE/GREY).  If no color specified, the default will be the same color of thread as the fabric.