Nominal vs. actual lumber sizes — what a 2x4 really measures (free printable PDF)
A “2x4” isn't actually 2 inches by 4 inches — a finished 2x4 measures 1½" × 3½". Lumber is named by its rough-cut size, then dried and planed smaller. Here's the real, finished size of every common board — download the free printable PDF or print it from the page.
Nominal vs. actual lumber sizes
| Nominal | Actual size (T × W) |
|---|---|
| 1×2 | ¾" × 1½"19 × 38 mm |
| 1×3 | ¾" × 2½"19 × 64 mm |
| 1×4 | ¾" × 3½"19 × 89 mm |
| 1×6 | ¾" × 5½"19 × 140 mm |
| 1×8 | ¾" × 7¼"19 × 184 mm |
| 1×10 | ¾" × 9¼"19 × 235 mm |
| 1×12 | ¾" × 11¼"19 × 286 mm |
| 2×2 | 1½" × 1½"38 × 38 mm |
| 2×4 | 1½" × 3½"38 × 89 mm |
| 2×6 | 1½" × 5½"38 × 140 mm |
| 2×8 | 1½" × 7¼"38 × 184 mm |
| 2×10 | 1½" × 9¼"38 × 235 mm |
| 2×12 | 1½" × 11¼"38 × 286 mm |
T × W = thickness × width. The 2×4 is highlighted — the size everyone asks about. Lengths are actual: an 8-ft 2×4 is a full 8 ft; only the cross-section shrinks. Figures are for surfaced (S4S) softwood dimensional lumber — the standard at any lumberyard or home center.
whatdrillbit.com
Why a 2×4 isn’t 2 by 4 inches
Lumber is named by its nominal (rough-cut) size — the dimension it’s cut to green, straight off the saw. Before it’s sold, the mill dries it and planes all four faces smooth, which shaves off about ¼" to ¾". So a board cut at a rough 2"×4" leaves the mill measuring 1½" × 3½" — the actual finished size. Every DIYer gets tripped up by this once; now you won’t.
The nominal name stuck as a convenient label — it’s what you ask for at the yard — but the board in your hand is the smaller, planed size in the chart above.
Lengths are the exception
Only the cross-section — thickness and width — gets reduced. Length is actual: an 8-foot 2×4 really is a full 8 feet, a 10-footer is 10 feet. So trust the stated length, but always plan around the smaller actual thickness and width.
Building with a 2×4? It’s actually 1½" thick — so it takes the 1½"-material pocket screw.
The right pocket-hole screw for a 2×4Common questions
What is the actual size of a 2x4?
A 2x4 is actually 1½ inches thick by 3½ inches wide (about 38 × 89 mm). The "2×4" is the nominal size — the rough dimension the board is named for before it's dried and planed smooth. Its length is exact, though: an 8-foot 2x4 really is 8 feet long.
Why is a 2x4 not actually 2x4 inches?
Lumber is named by its rough-cut size. A 2x4 starts as a board cut close to 2 by 4 inches, then it's dried and planed smooth on all four sides, which removes roughly ¼" to ¾". The finished, surfaced board that reaches the store measures 1½" × 3½" — smaller than the name it's sold under.
Are lumber lengths actual or nominal?
Lengths are actual. Only the cross-section — the thickness and width — is reduced by drying and planing. An 8-foot 2x4 is a full 8 feet, a 10-foot board is 10 feet, and so on, so you can trust the stated length even though the width and thickness measure smaller than the nominal name.
Gear for this job
As an Amazon Associate, WhatDrillBit earns from qualifying purchases.
Where these sizes come from
These are the standard, fixed actual sizes for surfaced (S4S) US softwood dimensional lumber — the same at any lumberyard or home center, not a source-to-source estimate like our pilot-hole numbers. They’re set by the industry softwood lumber standard; the millimetre figures are the conventional rounded metric equivalents.
These are the standard sizes for surfaced softwood dimensional lumber. Rough-sawn boards, hardwood sold by quarter (4/4) thickness, and some specialty or older stock can measure differently — when a dimension matters, measure the actual board.