Why is a 2x4 Actually 1.5x3 5?

Why is a 2x4 Actually 1.5x3 5?
Whether you're a homeowner or a do-it-yourselfer, you've likely wondered why is a 2x4 actually a 1.5x3.5 inch board? While this might not be the first thing that comes to mind, it's a commonly used size in construction, and the answer isn't as simple as it sounds.


When wood production first began in the United States, a timber that measured two inches by four inches was a bit of a stretch. Before mass production began, lumber was cut to order, and there were a variety of wood sizes and types. There was a lot of variation between locations, but it seemed that the forests of North America were an unlimited resource. A few decades after the turn of the century, the lumber industry was under great pressure to compete with alternatives such as concrete block and engineered products. This resulted in a lot of litigation and a lot of arguing over the best wood-sizing practices.


Eventually, the lumber industry settled on a new wood-sizing standard. The result was a more uniform size and more predictable dimensions. These new lumber standards have been refined over the last several decades, but the popular lexicon hasn't caught up with the new standard.


One thing to note is that the standard lumber sizes may vary by state. The lumber industry is currently under great pressure to compete with other market alternatives, and the size of a board doesn't necessarily tell you how well the wood will perform in a given situation. One example is that a 3x4 will actually roll off your tongue a little better than a 2x4.


Another reason for the size discrepancy is that a board that measures a nominal 2x4 will actually be a bit smaller than a real 2x4. During the heyday of 2x4 lumber, mills used to cut the wood to rough dimensions before cutting it down to a more reasonable size. This gave the timber a more uniform look, and it also gave mills a way to account for shrinkage as the wood dried. The finished size of a board, however, is usually exactly 1.5x3.5.


The best way to explain this discrepancy is to consider that the nominal 2x4 board isn't the actual 2x4 wood. The lumber is milled down to a smaller size to maximize its use. During this process, the width is reduced by about half an inch, and the thickness is reduced by a quarter inch. The board is then planed to its optimum size, which should yield a finished product that measures 1.5x3.5 inches.


The best way to figure out the true size of your wood is to measure it from the center of an interior wall. If you aren't an architect, you can also try to measure from the center of a door or window. A true contractor will be happy to help, but a novice do-it-yourselfer might not know which size is best. If you're doing a small project, you can probably find a 1.5x3.5 board.