Dimension of 2×4 (Quick Guide)
The real, finished dimension of a 2×4 is 1.5 inches by 3.5 inches. In metric, that equals 38 mm by 89 mm. The label “2×4” is nominal (the rough-cut name) and is larger than the final size after drying and planing.
Quick Answer
2×4 actual dimension: 1.5 in × 3.5 in (38 mm × 89 mm)
2×4 nominal dimension: 2 in × 4 in (before drying/planing)
Exact Dimensions Table
| Dimension | Inches (Actual) | Millimeters | Centimeters |
|---|---|---|---|
| Thickness | 1.5 | 38 | 3.81 |
| Width | 3.5 | 89 | 8.89 |
Why the Dimension Is Smaller Than the Name
Lumber is sawn at its nominal size, then kiln-dried and planed smooth (S4S). That process removes material from each face, giving the final, standardized size of 1.5″ × 3.5″ for a 2×4 in U.S./Canadian framing lumber.
Conversions & Formula
- Inches → millimeters:
mm = inches × 25.4 - 1.5 in × 25.4 = 38.1 mm → 38 mm (rounded)
- 3.5 in × 25.4 = 88.9 mm → 89 mm (rounded)
Related Pages
- 2×4 actual dimension
- 2×4 width: 3.5 inches (89 mm)
- 2×4 in mm: 38 × 89 • 2×4 in cm: 3.81 × 8.89
- 2×4 measurements (all units)
FAQ: Dimension of a 2×4
Is every 2×4 exactly 1.5 in × 3.5 in?
Yes for standard surfaced framing lumber. Small, acceptable variation can occur from mill tolerances and moisture.
Do pressure-treated 2x4s have the same dimensions?
Yes. They are surfaced to the same finished size; freshly treated boards can shrink slightly as they dry.
What about rough-sawn (“green”) 2x4s?
Rough-sawn pieces can be closer to the nominal dimension (around 1.75 in × 3.75 in). Retail framing lumber is typically surfaced to 1.5 in × 3.5 in.
Key Takeaway
The dimension of a 2×4 you actually build with is 1.5″ × 3.5″ (38 × 89 mm) — plan cuts and layouts using the actual size, not the nominal label.