This is a solid piece of clay, sold raw. However a layer of sealer is recommended before installation. It measures 8 3/4"" from top to bottom and 7 3/4"" left to right. Each piece covers about 36 sq in. Using a 1/2"" grout an average of 42 sq in will be covered with this piece (about 3.5 per sf). For a more accurate quantity, given a surface, give us a call to find out.