Lumber Dimensions: Nominal vs Actual Size Chart
Lumber is sold by nominal size but milled to smaller actual dimensions. A 2×4 is actually 1½″ × 3½″. This chart covers all standard S4S (surfaced four sides) softwood dimensional lumber. Rough-sawn lumber IS full nominal size.
Softwood dimensional lumber — S4S (surfaced four sides)
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1×2 | ¾ × 1½″ | 19 × 38 mm |
| 1×3 | ¾ × 2½″ | 19 × 64 mm |
| 1×4 | ¾ × 3½″ | 19 × 89 mm |
| 1×6 | ¾ × 5½″ | 19 × 140 mm |
| 1×8 | ¾ × 7¼″ | 19 × 184 mm |
| 1×10 | ¾ × 9¼″ | 19 × 235 mm |
| 1×12 | ¾ × 11¼″ | 19 × 286 mm |
| 2×2 | 1½ × 1½″ | 38 × 38 mm |
| 2×3 | 1½ × 2½″ | 38 × 64 mm |
| 2×4 | 1½ × 3½″ | 38 × 89 mm |
| 2×6 | 1½ × 5½″ | 38 × 140 mm |
| 2×8 | 1½ × 7¼″ | 38 × 184 mm |
| 2×10 | 1½ × 9¼″ | 38 × 235 mm |
| 2×12 | 1½ × 11¼″ | 38 × 286 mm |
| 4×4 | 3½ × 3½″ | 89 × 89 mm |
| 4×6 | 3½ × 5½″ | 89 × 140 mm |
| 6×6 | 5½ × 5½″ | 140 × 140 mm |
Common lengths
8 ft · 10 ft · 12 ft · 14 ft · 16 ft · 20 ft — not all sizes are available in all lengths. Check with your local supplier.
Rough-sawn vs S4S
Rough-sawn lumber IS the nominal size — a rough-sawn 2×4 is actually 2″ × 4″. S4S is planed smooth on all four sides, reducing dimensions by roughly ¼″–½″. Always use actual dimensions for structural calculations.