Lumber size calculator: what is the actual size of a 2 × 4?
1 1/2 × 3 1/2 in
a nominal 2 × 4, dressed dry (PS 20 Table 3) · green it is 1 9/16 × 3 9/16 in · for a nominal 2 × 4, dressed dry, from PS 20 Table 3
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
1 1/2 × 3 1/2 in
a nominal 2 × 4, dressed dry (PS 20 Table 3) · green it is 1 9/16 × 3 9/16 in
Source: PS 20-20 American Softwood Lumber Standard, Table 3 (U.S. Department of Commerce / American Lumber Standard Committee), read October 2, 2026. Data sheet (PDF)
A nominal 2 × 4 actually measures 1 1/2 × 3 1/2 inches, dressed dry, because softwood framing lumber is milled smaller than its name under the PS 20 standard. Pick your size and the dry or green state to read the real dimensions.
A worked example
A 1 × 8 pine board, dressed dry needs 3/4 × 7 1/4 in. A nominal 1 × 8 dresses to 3/4 inch thick and 7 1/4 inches wide: boards lose 1/2 inch of width up to 7 in, then 3/4 inch from 8 in up, which is why an 8 reads 7 1/4 and not 7 1/2.
Why is a 2x4 not actually 2 by 4 inches?
A 2 × 4 is a nominal name, not a measurement. The board starts near 2 by 4 inches rough-sawn and green, then it is dried and planed smooth on all four sides, which takes it down to the minimum dressed size the American Softwood Lumber Standard (PS 20) sets: 1 1/2 by 3 1/2 inches once dry. Wider boards lose more: up to 7 inches nominal a board loses 1/2 inch of width, but from 8 inches up it loses 3/4 inch, so a 2 × 8 is 1 1/2 × 7 1/4, not 7 1/2. Green lumber, sold unseasoned, is milled a little larger because it keeps shrinking as it dries toward that same dry size.
What else it is called
Lumber sizes are also searched as nominal versus actual, dressed size, or S4S, meaning surfaced four sides. A 2 × 4 is the nominal name; 1 1/2 × 3 1/2 in is the actual dressed size. The name stays the same across softwood species, so the dressed size on this page does not change with pine, fir or spruce.
Common sizes
| Nominal size | Actual, dressed dry | Actual, green |
|---|---|---|
| 1 × 2 | 3/4 × 1 1/2 in | 25/32 × 1 9/16 in |
| 1 × 3 | 3/4 × 2 1/2 in | 25/32 × 2 9/16 in |
| 1 × 4 | 3/4 × 3 1/2 in | 25/32 × 3 9/16 in |
| 1 × 6 | 3/4 × 5 1/2 in | 25/32 × 5 5/8 in |
| 1 × 8 | 3/4 × 7 1/4 in | 25/32 × 7 1/2 in |
| 1 × 10 | 3/4 × 9 1/4 in | 25/32 × 9 1/2 in |
| 1 × 12 | 3/4 × 11 1/4 in | 25/32 × 11 1/2 in |
| 2 × 2 | 1 1/2 × 1 1/2 in | 1 9/16 × 1 9/16 in |
| 2 × 3 | 1 1/2 × 2 1/2 in | 1 9/16 × 2 9/16 in |
| 2 × 4 | 1 1/2 × 3 1/2 in | 1 9/16 × 3 9/16 in |
| 2 × 6 | 1 1/2 × 5 1/2 in | 1 9/16 × 5 5/8 in |
| 2 × 8 | 1 1/2 × 7 1/4 in | 1 9/16 × 7 1/2 in |
| 2 × 10 | 1 1/2 × 9 1/4 in | 1 9/16 × 9 1/2 in |
| 2 × 12 | 1 1/2 × 11 1/4 in | 1 9/16 × 11 1/2 in |
| 4 × 4 | 3 1/2 × 3 1/2 in | 3 9/16 × 3 9/16 in |
| 4 × 6 | 3 1/2 × 5 1/2 in | 3 9/16 × 5 5/8 in |
| 6 × 6 | 5 1/2 × 5 1/2 in | 5 5/8 × 5 5/8 in |
Minimum dressed sizes from PS 20-20, the American Softwood Lumber Standard, Table 3. Dry is lumber at 19% moisture content or less, which is what most retail softwood is; green (unseasoned) lumber is milled a little larger so it reaches the dry size as it dries.
Where the numbers come from
- Dressed sizes: Voluntary Product Standard PS 20-20, American Softwood Lumber Standard (U.S. Department of Commerce), Table 3, Nominal and minimum-dressed sizes of boards, dimension, and timbers. At 19% moisture content (dry) a nominal 1 in dresses to 3/4 in and a nominal 2 in to 1 1/2 in; nominal widths lose 1/2 in up to 7 in and 3/4 in from 8 in up, so a 2 × 8 is 1 1/2 × 7 1/4 in. Green (unseasoned) lumber is milled slightly larger. Read October 2, 2026. Data sheet (PDF)
- Nothing here is calculated: the page looks up the dressed thickness and width for the nominal size you pick, in the dry or green column of the standard.
These are the minimum dressed sizes the standard allows, so a board can measure a hair over, and green lumber shrinks toward the dry size as it dries. Nominal 5 in and larger timbers are usually sold green and surfaced off the nominal by 1/2 to 3/4 in. The actual size does not change with the brand or the store, because it is the national standard, but your tape is the final word.
By Javier Miralles · Last updated . How this site is made.
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