We've had this question before. When you cut up a block for a d9p you lose half an inch of its size. This means you would need to start with a 9 patch that is 12.5" finished size to get a d9p that is 12" finished. Now if you want all your patches in the 9 patch to be the same size, that means each one is 4 1/6". That isn't easily cut. That's why this keeps coming up... there is no ***easy*** answer. (You can use different size blocks in the 9 patch, but some of them won't be squares, and it gets complicated cutting and putting together just the right ones.)