1. The size designation for most lumber, plywood, and other panel products. In lumber, the nominal size is usually greater than the actual dimension, thus, a kiln-dried 2" x 4" ordinarily is surfaced to 1-1/2" x 3-1/2". In panel products, the size is generally stated in feet for surface dimensions and increments of 1/16" for thickness. Product standards permit various tolerances for the latter, varying according to the type and nominal thickness of the panel.