📐 Lumber Dimensions Chart — Nominal vs Actual Sizes

The six answers people search for

Dimensional lumber names are rough-sawn sizes, not measurements — the numbers below are what the tape measure finds on surfaced (S4S) stock. If your question is in the cards, the answer is final; the tables underneath cover everything else.

🪵Every rack is sorted by a name that isn't the measurement

Every rack is sorted by a name that isn't the measurement

Why a 2×4 isn't 2 inches — the two-step shrink

The nominal name is a historical receipt. At the sawmill, a log is sawn into green (wet) boards at the stated size — a 2×4 leaves the head saw genuinely 2 inches by 4 inches. Then two operations shrink it. Kiln drying pulls the moisture content from above 30% down to around 15–19%, and wood contracts across the grain as it dries. Planing comes second: every board is surfaced on four faces (the S4S on the label) so that all boards of a nominal size are interchangeable — a wall framed in studs from three different mills still comes out flat because all of them are planed to the same final dimension, not the same nominal one.

The shrink is not arbitrary. The American Lumber Standard, published as Voluntary Product Standard PS 20 by the Department of Commerce and enforced through certification bodies including NELMA and the ALSC, fixes dressed sizes so that "a 2×4 is a 2×4" everywhere: boards under 2 inches nominal lose a quarter inch of thickness; dimension lumber 2 to 4 inches thick loses a half inch; widths up to 6 inches lose a half inch; widths of 8 inches and above lose three-quarters. Those four rules generate the entire table — if you remember them, you can derive any row from its name.

Nominal vs actual — the full chart

Filter by family, or read the whole dressed-size table in one pass. All values are surfaced four sides (S4S), the form every yard sells framing lumber and boards in; rough-sawn stock runs at full nominal size.

Source: dressed sizes per Voluntary Product Standard PS 20 (American Lumber Standard) as applied by the grading agencies (NELMA, ALSC-certified). Mill tolerance ±1/64″ on dressed faces. 1×14, 1×16 and 2×14 are standard sizes but thinly stocked at retail — confirm availability before designing around them.

Standard lumber lengths — 8 to 20 feet

Length is sold true to name: a 2×4×8 is 96 inches long (actual), unlike its cross-section. The rack depth thins as the number grows — 8- and 10-foot stock is everywhere, 20-foot rafters are a contractor-yard item — and price per board foot rises with length because long clear fiber comes from tall trees.

Pre-cut studs (92-5/8″ and 104-5/8″) are sold alongside full-length stock for standard wall heights — they save three plate-widths of cutting per wall and cost slightly less than 8-footers.

📏Trust the tape, not the stencil

Trust the tape, not the stencil

The quarter system: 4/4, 5/4, 6/4 and 8/4 lumber

The hardwood rack and the decking aisle measure thickness in quarters of an inch instead of nominal inches. The system counts rough-sawn quarter-inches: 4/4 ("four-quarter") is one inch rough, 5/4 is one and a quarter, 8/4 is two. Surfacing takes 3/16″ off hardwood faces (softwood decking 5/4 is surfaced to 1-1/16″), so the surfaced numbers below are what your project actually receives.

Hardwood surfaced thickness per standard S2S practice (13/16″ from 4/4); specialty shops offer S3S/S4S at slightly different finished sizes. Buy hardwood by the board foot — the board foot calculator converts quoted thickness × width × length into billable volume and price.

Studs and posts — where the dressed size does the work

The 1.5 × 3.5-inch stud is the module the whole framing system hangs on. Studs at 16 inches on center leave 14.5-inch clear bays — the opening insulation batts, electrical boxes and 14.5-inch blocking are all manufactured to fill. Gypsom board at 48 inches wide lands on exactly three bays, and a 4×8 plywood panel spans four — which is why the dressed size, not the nominal one, is the number every layout in construction assumes.

Posts run one size class up. A 4×4 post is 3.5 × 3.5 inches dressed, and pressure-treated 4×4s in 8-, 10- and 12-foot lengths are the fence and deck-post default. For deck guardrail posts and structural columns, note that 6×6 posts (5.5 × 5.5″ actual) are what most modern deck codes assume for tall or heavily loaded columns — the 4×4 remains fine for fences, gates and light-duty applications. Treated stock is sold wet: expect it to lose roughly 1/16–1/8″ per face as it dries, and seal cut ends with end-cut solution to keep the treatment envelope intact.

Metric conversions and species notes — reading the chart two other ways

Metric readers and importers meet the same dressed sizes expressed differently. A dressed 2×4 — 1.5 × 3.5 inches — is 38 × 89 mm, and that is the number stamped on European-made plans, on imported hardware packaging and on structural screws sold by length in millimeters. The rule of thumb: one inch equals exactly 25.4 mm, so every entry in the main table converts by multiplication — 5.5 inches (a dressed 2×6) is 139.7 mm, a dressed 4×4 at 3.5 inches is 88.9 mm. Plans drawn metric-first in Canada or the EU assume those dressed dimensions, which is why a "45×90 mm stud" from a metric lumber list is the same piece of wood as the American 2×4 — dressed, not nominal.

Species changes weight and grade, never the dressed size — a southern yellow pine 2×4 measures 1.5 × 3.5 inches exactly like spruce-pine-fir. What species does change is which sizes are commonly stocked: 2×4 pine studs in SYP country often come in longer 10-, 12- and 20-foot lengths than the SPF racks further north, and a 20-foot 2×4 is a stocked SKU in the south while a special order elsewhere. For woodworking lumber, the nominal system crosses species too — a 5/4 board in red oak and in poplar both surface to 1-1/16 inches, even though the two cost three times apart per board foot.

One last habit ties the whole chart together: read the grade stamp inked on the piece, not just the tape. Every American framing board carries a stamp with five facts — the certifying agency, the species or species group (SYP, SPF, DF-L), the grade number (No. 2, stud, No. 3), the moisture marking (S-DRY, MC-15, HT for heat-treated), and the mill identifier. The dressed size is fixed by the standard, but the grade and moisture marks tell you how the board will behave: S-GRN treated stock will shrink as it dries, HT stock is safe for furniture use, and a No. 3 grade at the same dressed size can carry dramatically less load than the No. 2 beside it. Wood sizes answer what the piece measures; the stamp answers what the piece is.

This chart is the lumber-side twin of the site's plywood sheet sizes chart — together they cover the rack from panel goods to framing stock. And when the dressed sizes feed a real calculation, the board foot calculator handles lumber volume and cost, while the plywood calculator on the homepage turns any surface into a sheet order. Anyone converting nominal lumber sizes for a cut list or a material order is exactly who this lumber dimensions chart was written for.

Last updated: November 2026 · Published by the Plywood Calculator team · Dressed sizes per Voluntary Product Standard PS 20 (American Lumber Standard); hardwood surfaced thicknesses per standard S2S practice.