Consumables
Dimensional Lumber
Dimensional lumber is softwood framing stock sold under a nominal size — 2x4, 2x6, 1x8, and so on — that names the board it started as, not the board you're holding. Buy a 2x4, measure it, and you'll get 1 1/2" by 3 1/2". That's not a bad batch or a rounding error; every 2x4 at every lumberyard measures the same, and the gap between the name and the tape measure is baked into the entire framing lumber industry on purpose.
Where the missing material actually goes
A "2x4" starts life at a sawmill genuinely close to 2" by 4" — rough-sawn, straight off the blade. Two things happen to it after that, and both remove real material:
- Drying. Green (freshly sawn) lumber is mostly water. Kiln-dried to the industry-standard 19% moisture content or below, it shrinks — wood loses dimension across the grain as it dries, the same physics behind the Wood Movement Estimator. That alone accounts for a meaningful chunk of the loss.
- Surfacing. Rough-sawn faces aren't flat, square, or splinter-free, so the board gets planed on all four faces — S4S (surfaced four sides) — to arrive at the smooth, uniform, stackable product actually sold. Planing removes more material than drying does.
Add the two together and a nominal 2" dimension lands at 1 1/2" actual — a 3/4" total loss split across both faces. It's a real, physical, unavoidable cost of turning a rough-sawn timber into something with a flat face and a consistent thickness, not an industry trying to quietly shortchange anyone.
The actual sizes
| Nominal | Actual |
|---|---|
| 1x2 | 3/4" x 1 1/2" |
| 1x3 | 3/4" x 2 1/2" |
| 1x4 | 3/4" x 3 1/2" |
| 1x6 | 3/4" x 5 1/2" |
| 1x8 | 3/4" x 7 1/4" |
| 1x10 | 3/4" x 9 1/4" |
| 1x12 | 3/4" x 11 1/4" |
| 2x2 | 1 1/2" x 1 1/2" |
| 2x3 | 1 1/2" x 2 1/2" |
| 2x4 | 1 1/2" x 3 1/2" |
| 2x6 | 1 1/2" x 5 1/2" |
| 2x8 | 1 1/2" x 7 1/4" |
| 2x10 | 1 1/2" x 9 1/4" |
| 2x12 | 1 1/2" x 11 1/4" |
| 4x4 | 3 1/2" x 3 1/2" |
The part that actually trips people up
The loss isn't a flat, predictable 1/2" across the board. Nominal widths of 6" and under lose exactly 1/2" (a 1x6 becomes 5 1/2"). Nominal widths of 8" and over lose 3/4" instead (a 1x8 becomes 7 1/4", not 7 1/2") — an industry convention, not a typo, and one worth knowing before you design a project around a shelf that "should" be 7 1/2" wide and comes home 1/4" short. Thickness doesn't have this quirk: a 2x anything is always 1 1/2" thick, full stop.
Why hardwood doesn't work this way
Walk into a hardwood dealer and ask for a "2x6" walnut board and you'll get a confused look — hardwood is sold rough-sawn or S2S (surfaced two sides, faces only, edges left rough) by actual thickness in quarters: 4/4 (four-quarter, roughly 1" rough), 8/4 (roughly 2" rough), and so on, priced by the Board Foot, not by a nominal name. There's no equivalent of "a 4/4 board is actually 3/4 inch" folk knowledge to memorize, because 4/4 was never claiming to be a full inch to begin with — it's telling you the rough thickness up front, before you've decided how much of it a project needs milled away. Dimensional lumber's nominal-vs-actual gap is a softwood-framing-specific convention, not how lumber sizing works generally.
What to check before you buy
- Grade and species stamp. Framing lumber is stamped with its grading agency, species group (SPF — Spruce-Pine-Fir — is the most common in North America, alongside Hem-Fir and Southern Yellow Pine), and moisture content at grading (KD or S-DRY for kiln-dried, S-GRN for green/unseasoned). A stud that was graded green can still shrink further after you've built with it.
- Actual, not nominal, in your plans. Any cut list, especially one mixing dimensional lumber with plywood (which is sold close to its actual stated thickness) or hardwood, needs the real 1 1/2" x 3 1/2"-style numbers, not the nominal name, or joints won't line up.
- Straightness. Framing-grade lumber isn't graded for the same straightness and stability furniture work wants — sight down every board before buying, not just at the yard's stated grade.