2×4 Actual Size
Convert nominal lumber sizes to actual sizes for fence posts, rails and boards.
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A 2×4 rail is 1½ in by 3½ in.
Why lumber is smaller than its name
Lumber is named by its rough-sawn size. Drying and planing take about ½ in off sizes up to 6 in and ¾ in off 8 in and wider boards, under the American Softwood Lumber Standard.
A 2×4 measures 1.5 × 3.5 in (38 × 89 mm). Covering 8 ft side by side takes 28 boards.
Nominal and actual sizes
| Nominal | Actual (dry) |
|---|---|
| 1 in | ¾ in |
| 5/4 in | 1 in |
| 2 in | 1½ in |
| 4 in | 3½ in |
| 6 in | 5½ in |
| 8 in | 7¼ in |
| 10 in | 9¼ in |
| 12 in | 11¼ in |
Under the American Softwood Lumber Standard (PS 20).
Common questions
Why is a 2×4 not 2 by 4 inches?
The name is the rough-sawn size. After drying and planing it is 1½ by 3½ inches.
Are fence pickets full size?
Not always. Many cedar pickets are 5/8 in thick instead of ¾ in, and dog-ear pickets are usually 5½ in wide.
Sources
- NIST, American Softwood Lumber Standard (PS 20): https://www.nist.gov/standardsgov/voluntary-product-standards-program