True Measurements of a 2×4
Despite the name, a construction 2×4 is not 2 inches by 4 inches. The true (actual) measurements of a standard, kiln-dried, surfaced 2×4 in North America are 1.5 inches by 3.5 inches. In metric, that is 38 mm by 89 mm.
Quick Answer
True size of 2×4: 1.5 in × 3.5 in (38 mm × 89 mm)
Why smaller? Boards are cut rough at nominal size, then dried and planed smooth, which removes material.
Exact Measurements Table
| Dimension | Inches (Actual) | Millimeters | Centimeters |
|---|---|---|---|
| Thickness | 1.5 | 38 | 3.81 |
| Width | 3.5 | 89 | 8.89 |
Nominal Size vs Actual Size
The label “2×4” is the nominal or rough-cut name. After kiln drying and planing (surfacing on four sides, S4S), the board finishes to its actual or true measurements listed above. This standard has been used for decades in U.S. and Canadian softwood framing lumber.
Related Conversions
- 2×4 in mm: 38 mm × 89 mm
- 2×4 in cm: 3.81 cm × 8.89 cm
- 2×4 width: 3.5 inches (89 mm)
- 2×4 actual dimension
FAQ: True Measurements of a 2×4
Are all 2x4s exactly 1.5 in by 3.5 in?
Yes for standard surfaced framing lumber. Minor variation can occur due to moisture and mill tolerances.
Do pressure-treated 2x4s have different true measurements?
No, they are surfaced to the same finished size. If very wet, they can shrink slightly as they dry.
What about rough-sawn or “green” 2x4s?
Rough-sawn boards can be closer to the nominal size (around 1.75 in by 3.75 in). Retail framing lumber is typically surfaced to 1.5 in by 3.5 in.
Key Takeaways
- True 2×4 size: 1.5 in × 3.5 in (38 mm × 89 mm).
- Nominal names stay for consistency; actual sizes are used for building.
- Measure boards when precision matters, especially in tight-tolerance projects.