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Lumber Measurements

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  • Lumber Measurements

    I'm sure this question has been asked before, but my search yield no results. Why does a 2x4 measure only 1.5 x 3.5? Best I can figure, the lumber companies must have been politicians first - promising one thing and delivering another!!

    Seriously, what is the reason - why does it measure a half inch less? Yes... I'm new to the world of wood -but learning fast.


  • #2
    Re: Lumber Measurements

    When a 2x4 is first sawed, it is sawed 2"x4". This is referred to as rough cut. It is then allowed to dry or is put in a kiln where it is forced to dry. That process causes the board to shrink slightly and because the shrinkage varies among boards the size of various pieces is then different. The dried lumber is then planed, to again make it uniform in size.


    • #3
      Re: Lumber Measurements

      I agree with Mr Moy. Go to a saw mill and buy rough lumber and it is the actual dimensions. If you want the rough lumber size in a planed board, they would rough cut it a quarter or half bigger.

      Now does anybody know if there was ever a time when the processed lumber came in a true, planed measurement. Or has the 1.5X3.5 been the standard since planed, processed lumber arrived on the scene?
      I'm on "The List" and I love it!!


      • #4
        Re: Lumber Measurements

        at one time about 40 years ago the standard was 1 5/8" X 3 5/8" inches for a 2x4,

        threads where this has been discussed before

        there has been a down sizing of the lumber over the years,
        For convenience, we refer to lumber by its nominal dimensions, which are larger than its actual fractional size (see above table). This difference occurs because nominal dimensions traditionally referred to rough lumber, whose size was reduced in drying and planing. In addition, the standard finished dimensions of lumber have decreased through time—the typical 13/16 inches for a 1-inch board in the 1910s was reduced by 4% in 1929 and by another 4% in 1956, resulting in the current standard of 3/4 inch.[2] The move to set national standards for lumber in the United States began with publication of the American Lumber Standard in 1924, which set specifications for lumber dimensions, grade, and moisture content; it also developed inspection and accreditation programs. These standards have changed over the years to meet the changing needs of consumers, manufacturers, and distributors, so that lumber would remain competitive with alternative construction products. Current standards are set by the American Lumber Standard Committee, appointed by the Secretary of Commerce.[3]

        Attempts to maintain lumber quality over time have been challenged by historical changes in the timber resources of the United States—from the slow-growing virgin forests common over a century ago to the fast-growing plantations now common in today's commercial forests. Resulting declines in lumber quality have shifted use to alternative construction products and have been of recent concern to both the lumber industry and consumers.[4][5]
        Last edited by BHD; 10-20-2009, 09:12 PM. Reason: typo
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        • #5
          Re: Lumber Measurements

          I agree with BHD... I can actually remember my Dad teaching me that a 2 by 4 was 1-5/8 by 3-5/8 inches, and as I recall, my purchases of such lumber was true to that dimension right up through the 70's.

          I had an absense from such things for most of the 80's and 90's, but when I returned to it in early 2000, things seemed about a 1/8-inch less than they used to be.

          So, either lumber has gotten a lot wetter and now shrinks considerably more.... OR, as I expect, the lumber mills are gaining a few extra boards out of each trunk by shaving a little from each customer's expectations.

          You may take note that 3/4 ply is not exactly 3/4-inches thick either. That may be with some brands and/or with some dealers and there's not a lot of consistancy with such sheet stock (actually there's not a lot of consistance with boards either). I've been building a lot of stock for shelving and I've noted that when buying a 1 x 10 it varies from 9-1/4 inches wide to 9-5/8 inches. Graded stock is also often somewhat less than the particular "grade" indicates too... with more knots, knock-outs, etc.

          So, whether buying sheet stock or "boards", I've just learned to check the dimensions closely on each piece as I'm working along.

          Bottom line is that lumber in 2009 is nether the same dimension or quality that it was 30 years ago.



          • #6
            Re: Lumber Measurements

            My dad built his house in the early 60's and purchased all of the floor joist from a wrecking company, they came out of a church they were tearing down. The lumber is planed on all four sides and measures 2 1/2" x 14" x 20' and all of them are yellow pine placed on 16" centers. Glad I was still in diapers, those things must have weighed a ton.

            Sorry to stray off topic, but what the other fellas said is correct.