What is the actual size of a 2x4?
A '2x4' is a nominal size — the actual dressed dimensions are 1½ × 3½ inches. Nominal dimension lumber is always smaller than its name once surfaced: 2x6 = 1½ × 5½, 2x8 = 1½ × 7¼, 2x10 = 1½ × 9¼, and 2x12 = 1½ × 11¼ inches. These finished sizes come from the American Softwood Lumber Standard (PS 20).
Source: American Softwood Lumber Standard (PS 20) · Verify against your AHJ and the adopted code edition.
Dimensional lumber is sold by its nominal size — the rough dimension before it’s dried and planed smooth. The actual (dressed, “S4S”) size is smaller. The most quoted example: a 2x4 is really 1½ × 3½ inches.
Common softwood sizes:
| Nominal | Actual (dressed) |
|---|---|
| 1x4 | ¾ × 3½ in |
| 1x6 | ¾ × 5½ in |
| 2x4 | 1½ × 3½ in |
| 2x6 | 1½ × 5½ in |
| 2x8 | 1½ × 7¼ in |
| 2x10 | 1½ × 9¼ in |
| 2x12 | 1½ × 11¼ in |
Two patterns make these easy to remember: 2x thickness is always 1½ inches, and from 2x8 up the face width is the nominal minus ¾ inch (a 2x8 is 7¼, not 7½). Below that, 2x4 and 2x6 lose a full ½ inch.
Rough-sawn or “full-dimension” lumber is the exception — it can measure at or near its nominal size — so confirm before you lay out tight tolerances.
Sources
- American Softwood Lumber Standard (PS 20) — U.S. Dept. of Commerce Voluntary Product Standard PS 20