Sound Smarter on the Jobsite: Lumber Dimensions

A 2x4 isn't really 2"x4", it's 1.5"x3.5". This is "nominal" vs "actual," and while it's pretty basic knowledge in construction world, I still see this mistake. Also, there's more to the story!

First of all, why is a 2x4 smaller than its name implies? Because of "kerf." When a saw cuts a piece of wood, the blade has thickness, and that thickness is taken out of the board. That's kerf. Boards are cut roughly from the tree first in dimensions closer to actual 2"x4". Then, they get "dressed" (a planer gets the board to its finished size/appearance) and/or dried (usually in a kiln, hence the term KD, more on that later). The kerf, drying, etc are subtracted from the original 2x4, making it smaller. You pay for a 2x4 bc you're paying for the process.

This is why in old houses, we see what we call "real 2x4's," which are *actually* 2"x4" (or even bigger) bc that's before the practice of counting kerf/drying as part of the board size (and before modern sawmill/lumber processing procedures in general). And it's why when you're working in old houses, you can do more structurally with the "same" lumber sizes - bc an older growth 100 yr old 2x4 is way stronger than a modern 2x4. It's one of the many reasons old houses are worth saving!