A 2x4 is a type of lumber that is cut to standardized width and depth, often specified in millimeters or inches. It is mainly used for construction framing, as well as finishing. In the past, a 2x4 actually measured 2 inches by 4 inches, but now most timber is milled and planed to give it a more finished look and a more consistent size and profile. As a result, a 2x4 no longer measures a full 2 inches by 4 inches. Instead, a 2x4 is actually 1 1/2 inches by 3 1/2 inches. The length of a board is usually specified separately from the width and depth. A 2x4 is the most common type of lumber used in the world and is used for framing houses and in part of just about every other type of project.