The thickness and weight of a granite countertop depends on the total dimensions of the piece. Larger pieces naturally have to be thicker and heavier than smaller pieces. They need to be able to support their own weight, in addition to the weight of other items placed on or in it. Usually, countertops for kitchens or sinks must also support sinks and other in-counter appliances. Additional thickness and mass are needed for granite countertops to do this.