A piece of stone may have a stated size such as 12” wide x 24” long x 1” thick, but when the stone is measured, both the size and the thickness are different than stated. There is a simple explanation for this. Stone suppliers have traditionally used nominal dimensions.
Nominal measurements (length x width) traditionally refer to the size of the stone without a grout joint. For example, in a natural cleft piece of 12”x24” bluestone, the actual size is cut smaller to allow for a grout joint when setting the stone.
Nominal measurements (thickness) traditionally refer to the average thickness of the stone. For example, 1” thick natural cleft flagging ranges in thickness from approximately ¾” to 1-¼” thick and 1-½” thick natural cleft flagging ranges in thickness from approximately 1-¼” to 2”.
Actual measurements are the “true” final size of the stone.