A 2×4 refers to thickness and width in inches and pronounced 2 by 4. It is not so to-day. Prior to the early 1950’s, the lumber was cut to 2″ thick and 4″ wide. Now they are cut and dressed to 1 ½” by 3 ½”, but still called a 2 by 4. The same goes for 2×3, 2×5, 2×6, 2×8, 2×10, 2×12. They are all generally ½” smaller in thickness + width than what their name implies.

How Big is a 2×4 S.P.F.

A piece of dressed 2×4 lumber actually measures 1 ½” thick and 3 ½”wide. In rough, not milled, a 2×4 is approximately 2” thick and approximately 4” wide. When wood is dressed from a rough to a smooth surface, it loses about ¼” from each of its four sides