2×4 Actual Size: 1.5 in × 3.5 in (38 mm × 89 mm)
Quick dimensions
| Label | Inches | Millimeters |
|---|---|---|
| 2×4 actual size | 1.5″ × 3.5″ | 38 mm × 89 mm |
| 2×4 width | 3.5″ (actual) | 89 mm |
| 2×4 thickness | 1.5″ (actual) | 38 mm |
You’ll also see this called 2×4 dimensions, 2×4 actual measurement, 2×4 true size, or 2×4 size in mm — they all mean the same thing shown above.
Why a “2×4” isn’t 2 inches by 4 inches
“2×4” is the nominal size (the rough-cut name). After milling, drying, and planing the board smooth, the actual size becomes smaller: 1½″ × 3½″. This has been the standard for decades, so builders and DIYers expect it.
Nominal vs. actual lumber sizes
| Nominal | Actual (inches) | Actual (mm) | Details |
|---|---|---|---|
| 2×4 | 1.5″ × 3.5″ | 38 × 89 | Main framing stud |
| 2×6 | 1.5″ × 5.5″ | 38 × 140 | Joists/rafters |
| 2×8 | 1.5″ × 7.25″ | 38 × 184 | Floor/roof members |
| 2×10 | 1.5″ × 9.25″ | 38 × 235 | Beams/joists |
| 4×4 | 3.5″ × 3.5″ | 89 × 89 | Posts |
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FAQ: 2×4 actual size
What is the actual size of a 2×4?
The actual size is 1.5 inches by 3.5 inches, which is 38 mm by 89 mm in metric.
Why is a 2×4 smaller than 2″ × 4″?
2×4 is the rough-cut (nominal) name. After the board is dried and planed smooth, it finishes at 1½″ × 3½″.
How wide is a 2×4?
The width is 3.5 inches (89 mm). The thickness is 1.5 inches (38 mm).
Are sizes the same everywhere?
In North America, yes. Specialty lumber or regional standards can vary, but for common softwood studs, 1½″ × 3½″ is the norm.