Actual lumber sizes (nominal vs dressed)

A board's nominal size — the "2x4" on the price tag — is the size it was sawn before drying and surfacing. What you actually hold is smaller, by an amount PS 20-25 fixes precisely for each of three item categories: boards, dimension lumber, and timbers. Every weight on this site uses the dressed figure, never the nominal one.

Boards (nominal thickness 3/8″ to 1-1/2″)

The common shorthand "nominal widths over 6 in. lose 3/4 in." is wrong at 7 in: a nominal 7 dresses to 6-1/2″ (6.5″) — losing only 1/2 in, same as the narrower widths. The break to 3/4 in doesn't start until nominal 8, which dresses to 7-1/4″ (7.25″). Source: PS 20-25 Table 3.

Dimension lumber (nominal thickness 2″ to 4-1/2″)

Dimension lumber has no 7, 9, or 11-in. nominal widths — those widths exist only as Boards, which is why there is no such thing as a 2×7 or a 2×9 stud. Green sizes (S-GRN, over 19% MC) are cut oversized across the board to allow room for shrinkage during seasoning, so every nominal above has two real dressed sizes, not one.

Timbers (nominal thickness 5″ and up)

Timbers don't use a lookup table — PS 20 fixes a bracketed offset from nominal instead: 1/2 in. off both thickness and width from 5 to 6 in. nominal, 3/4 in. dry (1/2 in. green) from 7 to 15 in., and 1 in. dry (1/2 in. green) from 16 in. up. The same rule applies to thickness and width independently.