I understand that the actual dimensions of dimensional lumber are slightly smaller than their nominal dimensions, like how a 2x4 is actually 1½" x 3½". Are there industry standard tolerances on how close a board needs to be to those sizes? When I search for this, I get results about tolerances for framing and assembly, not the boards themselves. For example, I'm looking for something like "the 1½" dimension on lumber must be within 1.50±0.05" over the entire board's length, and the 3½" dimension must be 3.50±0.08" over the entire board's length."

Are there similar tolerances for the form of the lumber? For example, "For boards 6' or shorter, they may not be bowed more than 1/4" and no more than 0.10" per foot, may not be crooked more than 1/4" and no more than 0.10" per foot, may not be cupped more than 0.10" at any cross section, and may not be twisted by more than 5 degrees and no more than 2 degrees per foot, and each end of the board must be perpendicular within 0.10".

The dimensions and form of the board may change over time due to environmental conditions, but there must be some standards for when they are initially cut, right?

  • Yes there are. Raw cut wood is actually 2x4.
    – Traveler
    Feb 26, 2023 at 3:44
  • For what purpose do you need this information?
    – RMDman
    Feb 26, 2023 at 4:42
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    It's possible those standards exist, but all that falls apart in the real world. Wood dries out and defects appear. Sometimes you send it back; sometimes you buy new; other times you make it work. Feb 26, 2023 at 5:34
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    '"For boards 6' or shorter, they may not be bowed more than 1/4" and no more than 0.10" per foot' That would be my dream lumber! I've seen stuff at the local big box store that would be perfect for the bows of a boat without any additional bending!
    – FreeMan
    Feb 26, 2023 at 19:54
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    Try shopping at a lumberyard, letting them know what you're looking for. Woodworking supply stores also often have some selection of higher-grade lumber that may be milled to a finished or near-finished size. I seem to remember there's a woodworking stack; you would probably find more detailed advice there.
    – keshlam
    Feb 27, 2023 at 20:42

1 Answer 1


There absolutely are standards. For dimensional lumber, the document you're looking for is the "National Grading Rule for Dimension Lumber." Here is a link to the 2012 version in PDF. This is way out of my wheelhouse though, so I won't try to turn the rules for skip, crook, cup, wane, and warp in to numbers for you. Good luck with it. It's a fun looking standard.

In the end, though, your local store probably has what they have. Get used to using your planer. Also: my experience has been that dedicated lumber yards tend to get better stuff than the big box stores.

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