2×4 lumber (4×2 in the UK, Australia and New Zealand) measures 2” by 4”.
Don’t believe that!
An amateur do-it-yourselfer, bringing home some 2x4s from his local hardware store, may find that his project comes up a little short, since 2x4s actually measure 1.5” by 3.5”.
Is this a prime example of false advertising? Actually, 2x4s used to measure 2” by 4” (more or less), but this was a very rough-hewn piece of wood by modern standards. The rise of sawmills and improved production techniques created the smaller dimensions; that extra half-inch is lost due to planning/sanding and the drying process (which creates shrinkage).
The length of a 2×4 can vary between six feet and 20 feet or more, and is specified separately.
Not only is the outdated size of 2” x 4” still used, but in fact all engineering specifications are based on the original, rough cut dimensions of the wood!