Cross Section
Nominal vs Actual
American standard lumber (North American) is sold by nominal dimensions which are larger than the actual finished size. The difference is due to planing (dressing) and drying shrinkage.
Nominal
2 × 4
Rough sawn
Actual
1.5 × 3.5"
38 × 89mm
Timber Dimensions (Nominal → Actual)
29 Sizes| Nominal (in) | Actual (in) | Actual (mm) | Dressed | Common Use |
|---|---|---|---|---|
| 1x2 | 3/4" × 1-1/2" | 19 × 38 | S4S | Trim, furring |
| 1x3 | 3/4" × 2-1/2" | 19 × 64 | S4S | Trim, shelving |
| 1x4 | 3/4" × 3-1/2" | 19 × 89 | S4S | Trim, siding |
| 1x6 | 3/4" × 5-1/2" | 19 × 140 | S4S | Trim, decking |
| 1x8 | 3/4" × 7-1/4" | 19 × 184 | S4S | Trim, shelving |
| 1x10 | 3/4" × 9-1/4" | 19 × 235 | S4S | Trim, flooring |
| 1x12 | 3/4" × 11-1/4" | 19 × 286 | S4S | Trim, shelving |
| 2x2 | 1-1/2" × 1-1/2" | 38 × 38 | S4S | Framing, blocking |
| 2x3 | 1-1/2" × 2-1/2" | 38 × 64 | S4S | Framing, furring |
| 2x4 | 1-1/2" × 3-1/2" | 38 × 89 | S4S | Wall framing, studs |
| 2x6 | 1-1/2" × 5-1/2" | 38 × 140 | S4S | Floor joists, rafters |
| 2x8 | 1-1/2" × 7-1/4" | 38 × 184 | S4S | Floor joists, beams |
| 2x10 | 1-1/2" × 9-1/4" | 38 × 235 | S4S | Floor joists, headers |
| 2x12 | 1-1/2" × 11-1/4" | 38 × 286 | S4S | Floor joists, beams |
| 4x4 | 3-1/2" × 3-1/2" | 89 × 89 | S4S | Posts, columns |
| 4x6 | 3-1/2" × 5-1/2" | 89 × 140 | S4S | Posts, heavy framing |
| 4x8 | 3-1/2" × 7-1/4" | 89 × 184 | S4S | Heavy framing, beams |
| 4x10 | 3-1/2" × 9-1/4" | 89 × 235 | S4S | Heavy framing, beams |
| 4x12 | 3-1/2" × 11-1/4" | 89 × 286 | S4S | Heavy framing, beams |
| 6x6 | 5-1/2" × 5-1/2" | 140 × 140 | S4S | Posts, large columns |
| 6x8 | 5-1/2" × 7-1/2" | 140 × 191 | S4S | Heavy posts, beams |
| 6x10 | 5-1/2" × 9-1/2" | 140 × 241 | S4S | Heavy beams, girders |
| 6x12 | 5-1/2" × 11-1/2" | 140 × 292 | S4S | Heavy beams, girders |
| 8x8 | 7-1/2" × 7-1/2" | 191 × 191 | S4S | Large posts, columns |
| 8x10 | 7-1/2" × 9-1/2" | 191 × 241 | S4S | Large beams, girders |
| 8x12 | 7-1/2" × 11-1/2" | 191 × 292 | S4S | Large beams, girders |
| 10x10 | 9-1/2" × 9-1/2" | 241 × 241 | S4S | Large columns |
| 10x12 | 9-1/2" × 11-1/2" | 241 × 292 | S4S | Large beams |
| 12x12 | 11-1/2" × 11-1/2" | 292 × 292 | S4S | Very large columns |
Timber Grades (ASTM Standards)
6 Grades| Grade | Description | Applications |
|---|---|---|
| Select Structural | Highest quality, minimal defects | Visible beams, heavy loads |
| No. 1 | High quality, minor defects allowed | Framing, general construction |
| No. 2 | Standard grade, moderate defects | Studs, joists, rafters |
| No. 3 | Utility grade, more defects | Sheathing, blocking |
| Stud Grade | Specific for wall framing | Wall studs |
| Construction Grade | Good quality, mixed use | General framing |