Why are all lumber measurements a 1/4" to 1/2" shorter than what they say it is?

Answer 1

that would be the size before they finish it or rough cut.

Answer 2

Lumber goes thru many steps before it gets to your local lumber company for sale to the general public.
Years ago, and in some areas, when the lumber mills sold lumber it was generally cut to a specific dimension which started with an inch. They were cut to as close to the one inch thickness as they could get them, and the width could be most anything the customer desired. The measurement was always the exact amount that the board was called, a 1x4 was 1 inch by 4 inches, a 2x4 was 2 inches by 4 inches and so on. This lumber was green, fresh out of the woods, and rough cut, (sawn by large toothed saws, that usually left a groove with every stroke). The boards also varied as to exact measurement from one spot to the next several inches down. If you wanted a smooth board you had to use a hand plane or a draw knife to get it to that point. Nowadays the lumber is cut in a sawmill by a giant band saw, pushed down a conveyor belt to a drying rack where it's stacked and dried, sometimes for weeks, before it's put through a planer, to get the rough spots out. Then it's cut to length and shipped to the lumber yard where you buy it. The drying lumber shrinks as the moisture leaves the wood and the planing procedure takes off another small chunk of thickness and width. Length should still be accurate, or in most cases a little longer than the stated length to allow for squaring up the board ends, but the widths will always be 1/2"- 5/8" less than the stated size, thickness usually a 1/4" - 1/2" less.

Answer 3

Well, at the mills,they cut let's say a 2x4. That would be a ruff cut. Then they run it through a planer to get a finished smooth cut. The actual ruff cut size is what they go by. But now I heard that is no longer the case,in the state of California.

Answer 4

This is called "nominal sizing". This is the size of the stock before planing for smoothness. In the old days they used the true dimensions but over a period of time the market wanted a prettier product. It was easier to leave the reference the same because of all the code books and reference materials out there. Well, there is my carpenter's trivia; my apprenticeship wasn't wasted.

;- )