4x4 Actual Size
The real dimensions of a nominal 4x4, and what it's commonly used for.
| Measurement | Value |
|---|---|
| Nominal size | 4x4 |
| Actual thickness | 3-1/2" |
| Actual width | 3-1/2" |
| Board feet per linear foot | 1.333 |
| Approx. weight per linear foot | 3.30 lb (kiln-dried softwood) |
| Common uses | Deck posts, fence posts |
Why a 4x4 measures 3-1/2" × 3-1/2"
Like all dimensional lumber, a 4x4 starts life close to its nominal size before it's dried and planed smooth on all four sides. That process removes roughly 1/2 inch from each dimension, leaving the actual, finished size you buy at 3-1/2" × 3-1/2". This is standard across every softwood lumberyard in the US, not specific to any one supplier.
Where these numbers come from
Actual dimensions reflect the American Softwood Lumber Standard (PS 20) size for surfaced dry (S-DRY) dimension lumber. Weight is an approximate figure for kiln-dried softwood framing lumber and varies somewhat by species and moisture content.
Frequently asked questions
Is a 4x4 really 4 by 4 inches?
No -- like all dimensional lumber, the 4x4 name describes the rough size before milling. After drying and planing, the actual size is 3-1/2" × 3-1/2".
Does this size vary by species?
The actual dimension is standardized across species for a given nominal size, though weight per linear foot varies somewhat since different softwood species have different densities.
What is a 4x4 commonly used for?
Deck posts, fence posts.
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