Wood · Sizes
Lumber sizes: nominal and actual
The name is the rough-sawn size; the board you buy is smaller after drying and planing. A 2x4 is actually 1½ × 3½ inches (38 × 89 mm), a 2x6 is 1½ × 5½, a 4x4 is 3½ × 3½ and a 1x6 is ¾ × 5½. Up to 6 inches wide the dressed size is half an inch less than the name; from 8 inches, three quarters less. Board feet are counted on the nominal size: the board foot calculator does it for any piece.
Softwood lumber, dry and dressed (PS 20)
| Nominal | Actual, inches | Actual, mm | Board feet per linear foot |
|---|---|---|---|
| 1 × 2 | ¾″ × 1½″ | 19 × 38 | 0.167 |
| 1 × 3 | ¾″ × 2½″ | 19 × 64 | 0.250 |
| 1 × 4 | ¾″ × 3½″ | 19 × 89 | 0.333 |
| 1 × 6 | ¾″ × 5½″ | 19 × 140 | 0.500 |
| 1 × 8 | ¾″ × 7¼″ | 19 × 184 | 0.667 |
| 1 × 10 | ¾″ × 9¼″ | 19 × 235 | 0.833 |
| 1 × 12 | ¾″ × 11¼″ | 19 × 286 | 1.000 |
| 2 × 2 | 1½″ × 1½″ | 38 × 38 | 0.333 |
| 2 × 3 | 1½″ × 2½″ | 38 × 64 | 0.500 |
| 2 × 4 | 1½″ × 3½″ | 38 × 89 | 0.667 |
| 2 × 6 | 1½″ × 5½″ | 38 × 140 | 1.000 |
| 2 × 8 | 1½″ × 7¼″ | 38 × 184 | 1.333 |
| 2 × 10 | 1½″ × 9¼″ | 38 × 235 | 1.667 |
| 2 × 12 | 1½″ × 11¼″ | 38 × 286 | 2.000 |
| 4 × 4 | 3½″ × 3½″ | 89 × 89 | 1.333 |
| 4 × 6 | 3½″ × 5½″ | 89 × 140 | 2.000 |
Sizes are the dry dressed sizes of the American Softwood Lumber Standard (PS 20); green lumber is slightly larger, and hardwoods and metric timber (in Europe, 45 × 95 mm and similar) follow other rules. Board feet are by nominal size, the way lumber is priced.
Questions people ask
- What is the actual size of a 2x4?
- 1½ × 3½ inches, 38 × 89 mm. The 2 × 4 inches is the size before drying and planing.
- Why is a 2x4 not 2 by 4 inches?
- The name is the rough-sawn size. Drying shrinks the board and planing (dressing) the four faces takes off the rest: half an inch in each dimension up to 6 inches, three quarters of an inch from 8 inches up.
- What size is a 2x6 and a 2x8?
- A 2x6 is 1½ × 5½ inches (38 × 140 mm) and a 2x8 is 1½ × 7¼ inches (38 × 184 mm).