A common construction lumber designation, such as “2×4,” does not refer to the actual dimensions of the wood. This nomenclature is a nominal size established before the wood is surfaced or dried. Consequently, the final product is smaller than the stated dimensions.
This practice originated historically as a method to account for shrinkage during the milling and drying processes. The stated size reflected the approximate dimensions of the green, rough-cut lumber. Over time, as milling techniques became more refined, the finished size decreased, but the nominal size remained unchanged. This convention simplifies material specification and ordering within the construction industry.