Situation: Disappearing 9 patch using layer cake. After sewing the 9 patch together cutting is not a problem using the lines on a 24x36 mat and a 6x24 ruler I have.

Possible problem: After cutting the 9 patch into quarters the blocks would be 14 1/2 inches. The largest square ruler I have now is a 12 1/2 x 12 1/2. So to square the block should I just use the measurement lines on the mat or is it easier to get the huge 15 inch square ruler?

Would appreciate your opinions .....