This is a solid piece of clay, shaped in an octagon pattern, sold raw. However a layer of sealer is recommended before installation. It measures 11.5"" from parallel side to side, each side is about 4.75"" long. Each piece covers about 109 sq in. Using a 1/2"" grout an average of 133 sq in will be covered with one piece, this is a rough estimate to compute how many pieces you need. To calculate how many pieces you will need, just multiply your square footage by 1.083; that will give you the answer. However, if you are planning on using the 5""x5"" inserts, then one square foot is covered by one of each (one octagon and one insert).