Except that a "2x4" is typically 1½ × 3½ . Quoting https://en.wikipedia.org/wiki/Lumber#North_American_softwoods https://en.wikipedia.org/wiki/Lumber#North_Amer

Except that a "2x4" is typically 1½ × 3½ . Quoting https://en.wikipedia.org/wiki/Lumber#North_American_softwoods https://en.wikipedia.org/wiki/Lumber#North_American_softwood... : > a "2x4" board historically started out as a green, rough board actually 2 by 4 inches (51 mm × 102 mm). After drying and planing, it would be smaller, by a nonstandard amount. Today, a "2x4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is reliably 1½ by 3½ inches (38 mm × 89 mm).