Dimensional lumber, commonly referred to by its nominal size, undergoes a process of surfacing or dressing at the mill. This process reduces the rough-cut dimensions to a standardized, smaller size. Therefore, a piece of lumber designated as a “2 x 6” does not measure precisely two inches by six inches. The actual dimensions are typically 1.5 inches by 5.5 inches.
The discrepancy between nominal and actual dimensions arose historically from the need for lumber to be dried and surfaced, resulting in material loss. Maintaining the nominal size designation, while providing the reduced actual size, simplifies construction planning and material ordering. It allows builders and designers to account for standard material dimensions in their calculations, facilitating accurate project execution.
