I must admit I never actually checked mine. I generally use my 6" wide Omnigrip and if I need wider, I butt up my 6 1/2" square, also Omnigrip. I do also use my mat from time to time, if it's a larger piece there's more room for fudge factor. But as a matter of interest, I'm going to check all my rulers and mats. My DH will think I'm a right saddo, he already thinks I'm anal about these things! LOL