Why are 2" x 4"s Not Two Inches by Four Inches?

Many do-it-yourselfers have discovered that the two by fours they bring home from the lumber supply store are not actually two inches thick or four inches wide. The actual dimensions of standard two by fours can vary somewhat, but a true measurement of 1.5 inches by 3.5 inches is not unusual. So is the designation of two by fours a misnomer? Not necessarily. The lumber industry is nothing if not consistent with its measuring system. When harvested trees are brought to commercial sawmills for processing, the first cuts can be rough indeed. Many of the irregular outer planks are discarded immediately. The usable lumber is often sawn into easily divisible multiples of two, such as 24-foot, 12-foot and 6-foot lengths. Many two by fours sold for home use are cut into refreshingly consistent 6-foot lengths. Indeed, at one point in the milling process, two by fours actually do measure two inches by four inches. This is the measurement of the planks just before they are run through a machine ...  more