The minimum thickness for a granite slab for countertop use is 1¼ inches. Thinner slabs are more prone to cracks and chips, and can be a problem for the overhang and other portions that have no underlying supporting structures. You can get a thicker slab if you want, but there is really no need. If you do decide on a thicker slab, you have to make sure that you have the right amount of support.