Lumber Sizes: Nominal vs Actual (2x4, 2x6 and More)
Part of Interior & Finishes
Quick answer
Lumber is named by its nominal (rough) size, but the actual finished size is smaller. A 2x4 is really 1.5 × 3.5 inches, and a 2x6 is 1.5 × 5.5 inches, because the board is planed and dried after it's cut.
The name of a board — '2x4,' '2x6' — is its nominal size, set when the lumber is first rough-sawn. After it's dried and planed smooth on all four sides, it ends up smaller. That finished number is the actual size, and it's what you build with.
Dimensional lumber size chart
| Nominal | Actual (inches) |
|---|---|
| 1x4 | 0.75 × 3.5 |
| 1x6 | 0.75 × 5.5 |
| 2x2 | 1.5 × 1.5 |
| 2x4 | 1.5 × 3.5 |
| 2x6 | 1.5 × 5.5 |
| 2x8 | 1.5 × 7.25 |
| 2x10 | 1.5 × 9.25 |
| 2x12 | 1.5 × 11.25 |
| 4x4 | 3.5 × 3.5 |
| 6x6 | 5.5 × 5.5 |
The rule behind the chart
- Thickness: a nominal 1 in is 3/4 in actual; a nominal 2 in is 1.5 in.
- Width under 8 in: subtract 1/2 in (a 2x6 → 5.5).
- Width 8 in and up: subtract 3/4 in (a 2x8 → 7.25).
- Lengths (8, 10, 12 ft) are the real length — only thickness and width shrink.
Board-foot calculations for rough hardwood use the rough (nominal-ish) dimensions, while framing math uses these actual sizes — keep the two straight when estimating.
FAQs
Why isn't a 2x4 actually 2x4?
It starts at a rough 2×4 inches when sawn, then loses material when it's dried and planed smooth, finishing at 1.5 × 3.5 inches.
How thick is a 2x4?
A 2x4 is 1.5 inches thick and 3.5 inches wide. The '2' and '4' are nominal sizes, not the finished dimensions.