Based on standard dry-dressed size conventions. Actual products may differ according to surfacing, moisture condition, special milling, or product specification.

Nominal lumber size is a commercial trade designation, distinct from the board’s finished dimensions. The rough-sawn size before drying and surfacing is closer to the nominal number, but drying and planing reduce the final dimensions to the standard dressed size.

Nominal dimensions are useful for ordering, but actual dimensions are necessary for precise layout and material calculations.

Rough-sawn dimensions start closer to the nominal 2 by 4 in size. Drying shrinkage reduces the board slightly as moisture leaves the wood, and planing to a smooth, uniform surface removes additional material from all four sides. The nominal designation remains a conventional trade name; it is not a promise that the board originally measured exactly 2 by 4 inches at every manufacturing stage.

Larger timbers and specially milled products can follow different sizing rules than standard dimension lumber; verify against the specific product specification.

A conventional surfaced-dry 1x board is 3/4 in thick, subject to the relevant product specification.

Post size, timber classification, treatment, and actual dimensions can involve different product availability and rules than standard 2x boards. Do not assume every large beam follows the same reduction pattern as 2x lumber.

Larger sections such as 6×6, 6×8, and 8×8 exist as both rough-sawn timbers and surfaced products, with actual dimensions depending on the specific product and mill. Provide only standard-verified or manufacturer-verified dimensions for these larger sizes rather than assuming they follow the same reduction pattern as smaller dimension lumber. For structural selection of large beams, see the Wood Beam Span Chart.

Longer lengths and availability depend on species, grade, size, region, and supplier. Nominal cross-sectional dimensions (such as 2×4) do not determine the length a board is stocked in.

Ordinary 2×4 and 2×6 studs are commonly available as full-length stock or as precut studs sized to coordinate with standard wall heights once plates are added. Precut stud length and quantity depend on the specific wall assembly and plate configuration; detailed wall-spacing and structural capacity tables remain on their dedicated pages rather than being duplicated here.

Green lumber is often dressed larger to account for subsequent shrinkage. Do not claim that green lumber universally equals rough lumber; they are separate concepts describing moisture condition and surfacing status respectively.

Rough-sawn lumber has not been planed and typically measures closer to its full nominal dimension. S2S means surfaced two sides, and S4S means surfaced four sides, referring to how many faces have been planed smooth. Nominal trade sizes, standard dressed dimensions, and custom mill dimensions are three distinct concepts.

The current American Softwood Lumber Standard is DOC PS 20-25, which supersedes PS 20-20 Revision 1. Developed under U.S. Department of Commerce procedures at the initiation of the American Lumber Standard Committee, PS 20-25 became effective for products produced under it beginning January 2025. It governs product definitions, minimum dressed dimensions, moisture conditions, and lumber grading and marking. Many existing lumber-size references still cite the older PS 20-20 edition.

A grade stamp typically communicates species identification, lumber grade, the certifying inspection agency, the producing mill, and moisture designation at the time of surfacing. Common visually graded categories vary by species group and grading agency. Grade stamps communicate quality and identification information; they are distinct from a board’s physical dimensions, which follow the applicable dimensional standard separately.

Moisture condition connects to actual dimensions and dimensional movement, but an individual board will not always shrink by one predictable amount; actual movement depends on species, initial moisture, and drying conditions.

Hardwood is often sold by rough quarter-inch thickness designations such as 4/4, 5/4, 6/4, and 8/4, referring to quarters of an inch in rough thickness before surfacing. The National Hardwood Lumber Association rulebook provides standardized rough and surfaced thickness guidance for hardwood, which differs from the softwood nominal-to-actual dressed-size convention used throughout the rest of this chart. Do not apply softwood conventions to hardwood boards.

A 2×4 converts to approximately 38 by 89 mm, based on its actual dimensions, not its nominal label. Converting the nominal “2×4” directly would incorrectly suggest 51 by 102 mm.

This is used for volume estimates and basic geometry, not as a standalone structural-capacity check; see the Joist Span Chart for span-based structural sizing.

An 8-ft 2×4 (actual board feet = 3.5) in kiln-dried softwood commonly weighs in the range of roughly 9 to 13 lb, depending on species density, which for common softwoods ranges from approximately 23 to 39 lb/ft³ at typical moisture content. Avoid universal weights for all 2x4s, since species and moisture content both affect mass significantly.

Explain waste, cuts, openings, spacing, and stock-length selection using project-specific calculators for detailed material lists; see the Lumber Calculator and Framing Calculator rather than duplicating full material-list logic here.

Actual depth, width, species, grade, span, spacing, loading, and service conditions all matter for structural capacity. Span-table methodology combines these inputs rather than relying on nominal size alone. See the Lumber Span Chart, Floor Joist Span Chart, Roof Rafter Span Chart, and Header Span Chart for the specialized span data instead of relying on dimensional size alone.

Ordinary solid-sawn lumber follows the nominal-to-actual conventions covered throughout this chart, while engineered products such as LVL, glulam, and I-joists often have manufacturer-specific dimensions. These engineered products should not automatically be converted using ordinary nominal lumber tables. See the LVL Span Chart and Glulam Beam Size Chart for those product-specific dimensional references.

Conventional pressure-treated dimensional lumber generally uses the same familiar nominal sizes as untreated lumber, but physical dimensions, moisture, milling, and product specifications still need verification for the specific product. Preservative treatment is distinct from structural grade; treatment tags and use categories communicate chemical treatment and intended exposure, not size or strength grade information.

Distinguish ordinary lumber, specialty 5/4 decking, and wood-composite products; never treat their dimensions as universally identical. See the Decking Calculator and Deck Post Size Chart for related deck-specific sizing.

Applicable U.S. retail labeling requirements distinguish nominal descriptions from prominently displayed actual or minimum surfaced sizes. Verify dimensions before buying, especially for critical fit applications.