Ok, when we frame a block we have to remember that goes on each side, so an 8" center with a 2" frame is now 12" (8+2+2). I had a project like that last year where it started with a 6" block and a 2" frame and I was designing for 8" and was somehow surprised when it came out a lot bigger at 10"!
So it depends on how big you want to make those QST, can easily be 2", 3", or 4" inches for the total of 12". Remember that you also need one for the corners, so add that to the count.