Same here with the oven measurements. That's why I went and got 8 1/2" square quarry tiles, to make a 17" square. Even with that, I still had to shave a wee bit off. I'd think 8 1/4" would be a little safer, if you want to make absolutly sure it fits. But definitely do the quarry tile thing...those actual pizza stones are not only expensive, but as Pierre unfortunately discovered, not very well made in general.