Why is a 2 x 4 not 2″ x 4″ ?

Nominal vs Actual

Have you ever gone to the lumber store to pick up some wood and wondered why the 2 x 4’s are actually 1-½ x 3-½ inches? At first it could seem like false advertising, or that over time the sizes just got smaller, sort of like the burgers at your favorite fast food place. Fortunately, there is a reason for the madness that we call “actual size” and “nominal size”.

The nominal (named) dimensions of lumber are larger than the actual dimensions of dry, finished lumber. This is because when lumber is first cut it contains high moisture content that evaporates upon being kiln dried, causing the lumber to shrink. Once the wood is dry it is planed to the standard finished sizes. This is why a 2-inch x 4-inch board ends up measuring 1-½ inches x 3-½ inches once the process is finished.

Now it probably would make more sense for stores just to label lumber as its actual finished size, but it would also make more sense to spell Colonel Sanders as Kernal Sanders. I guess some things just are the way they are. Hopefully this clears up some confusion, or at least answers the question of why a 2 x 4 is not actually a 2” x 4”.

Now in some cases you may need an actual 2 x 4-inch piece of lumber, luckily there is a solution. Most specialty lumber mills will be able to provide actual dimensional lumber upon request, and in many cases you can even be specific with the desired moisture content. This will ensure that your finished piece will not shrink beyond reason and will be ready to work once received. We hope you have fun with your next project and that this information helps in one way or another!


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