Quick Answer
Exact Dimensions of a 2×4: 1.5″ × 3.5″ (38 mm × 89 mm)
The **exact, finished size** of a standard North American 2×4 is 1.5 inches thick by 3.5 inches wide.
In metric, that’s 38 mm × 89 mm. The length (8′, 10′, 12′, etc.) depends on what you buy.
Exact measurements (inches, mm, cm)
| Measurement | Inches | Millimeters | Centimeters |
|---|---|---|---|
| Thickness (exact) | 1.5″ | 38 | 3.8 |
| Width (exact) | 3.5″ | 89 | 8.9 |
You may see slight, acceptable variation from moisture and milling tolerances, but the **spec** is 1.5″ × 3.5″.
Nominal vs actual (why the “2×4” name is bigger)
“2×4” is the nominal size—the rough-cut name. After kiln drying and planing the faces smooth (S4S), material is removed, leaving the **actual** dimensions of 1½″ × 3½″. This has been the North American standard for decades.
Compare to other exact lumber sizes
| Nominal | Actual (inches) | Actual (mm) | More |
|---|---|---|---|
| 2×4 | 1.5 × 3.5 | 38 × 89 | 2×4 actual size (home) |
| 2×6 | 1.5 × 5.5 | 38 × 140 | 2×6 actual size |
| 2×8 | 1.5 × 7.25 | 38 × 184 | 2×8 actual size |
| 2×10 | 1.5 × 9.25 | 38 × 235 | 2×10 actual size |
| 4×4 | 3.5 × 3.5 | 89 × 89 | 4×4 actual size |
FAQ: Exact dimensions of a 2×4
What are the exact dimensions of a 2×4?
1.5 inches × 3.5 inches (38 mm × 89 mm). Length varies by board (8′, 10′, 12′, etc.).
Are the exact dimensions the same for pressure-treated 2×4s?
Typically yes—finished size is the same. Treated boards can feel slightly “fuller” when very wet, then shrink as they dry.
Do rough-sawn 2×4s have different measurements?
Rough-sawn (unsurfaced) boards can be closer to the nominal size (e.g., ~1.75″ × 3.75″). Retail framing lumber is surfaced to 1.5″ × 3.5″.