The industry standard for granite countertop thickness is typically around 3 centimeters for granite kitchen island countertops and 2 centimeters for bathroom granite and marble vanity tops. Thicker, 2-inch granite slabs have grown in popularity for interior design but do not add any significant structural advantages. Thicker granite slabs are much more rare and, therefore, more expensive, which is why they are most often used on smaller areas such as kitchen islands.