Nominal vs Actual Lumber Sizes
A "2x4" is not 2 by 4 inches - it is really 1½ by 3½. Lumber is named at its rough-sawn nominal size and finishes smaller once it is dried and planed. Here is the full nominal-vs-actual chart in inches and millimetres, and which size to use when.
By the Calculate My Reno Team / Published
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A “2x4” is not 2 inches by 4 inches. It is really 1½ × 3½. Softwood lumber is named at its nominal size - the rough dimension it is first sawn to - and ends up smaller after it is dried and planed smooth. The name sticks, the size shrinks.
The short answer
A standard 2x4 measures 1½ in × 3½ in (38 × 89 mm). Every “2x” board is 1½ in thick; the width is what changes. Boards up to 6 inches nominal lose ½ inch, and 8 inches and wider lose ¾ inch.
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If you only need board feet, the board foot calculator takes the nominal size you type and works out the volume and cost - no need to convert to actual first.
Why nominal and actual differ
Two steps shrink the board between the sawmill and the shelf:
- Drying. Green lumber is sawn slightly oversize, then kiln- or air-dried, which shrinks it.
- Surfacing. It is planed smooth on all four sides (S4S), taking off more wood for a clean, consistent finish.
The finished sizes are fixed by the American Softwood Lumber Standard (PS 20), so a 2x4 is the same 1½ × 3½ at any yard in North America.
Lumber size chart (nominal vs actual)
Standard dry, surfaced (S4S) softwood sizes:
| Nominal | Actual (inches) | Actual (mm) |
|---|---|---|
| 1 × 2 | ¾ × 1½ | 19 × 38 |
| 1 × 3 | ¾ × 2½ | 19 × 64 |
| 1 × 4 | ¾ × 3½ | 19 × 89 |
| 1 × 6 | ¾ × 5½ | 19 × 140 |
| 1 × 8 | ¾ × 7¼ | 19 × 184 |
| 1 × 10 | ¾ × 9¼ | 19 × 235 |
| 1 × 12 | ¾ × 11¼ | 19 × 286 |
| 2 × 2 | 1½ × 1½ | 38 × 38 |
| 2 × 3 | 1½ × 2½ | 38 × 64 |
| 2 × 4 | 1½ × 3½ | 38 × 89 |
| 2 × 6 | 1½ × 5½ | 38 × 140 |
| 2 × 8 | 1½ × 7¼ | 38 × 184 |
| 2 × 10 | 1½ × 9¼ | 38 × 235 |
| 2 × 12 | 1½ × 11¼ | 38 × 286 |
| 4 × 4 | 3½ × 3½ | 89 × 89 |
| 4 × 6 | 3½ × 5½ | 89 × 140 |
| 6 × 6 | 5½ × 5½ | 140 × 140 |
Which size do I use - nominal or actual?
- Board feet and ordering: use the nominal size. A 2x4 is figured 2 by 4. See how to calculate board feet and what is a board foot.
- Fit and framing layout: use the actual size. When you are working out how studs stack up, how thick a wall is, or whether a board fits an opening, the 1½ × 3½ is what matters.
Metric and regional sizes
Outside North America the same framing timber is sold in millimetres - a 2x4 equivalent is 38 × 89 mm, and in the UK regularised/CLS stud is commonly 38 × 89 mm too. Timber there is quoted at the nominal (sawn) size, with planed (PAR) stock finishing a few millimetres smaller per face. Hardwood is a separate world: it is sold rough in quarter-inch thicknesses (4/4, 5/4, 8/4) and close to its full nominal size.
The quick takeaways
- A 2x4 is 1½ × 3½, a 2x6 is 1½ × 5½, a 2x8 is 1½ × 7¼.
- Thickness of any 2x board is always 1½ in; 1x boards are ¾ in.
- Use nominal for board feet and ordering, actual for fit.
Frequently asked questions
What is the actual size of a 2x4?
A 2x4 is actually 1½ inches by 3½ inches (38 × 89 mm). The "2 × 4" is the nominal size - the rough size the board is sawn to before it is dried and planed smooth, which takes about a quarter inch off the thickness and a half inch off a 4-inch face.
Why is a 2x4 not actually 2x4 inches?
Two steps shrink it. The board is first rough-sawn close to 2 × 4, then it is dried, which shrinks it slightly, and planed smooth on all four sides, which removes more. The finished, surfaced board is 1½ × 3½ in. The standard sizes are set by the American Softwood Lumber Standard (PS 20), so a 2x4 is the same size at any yard.
What is the actual size of a 2x6, 2x8 and 2x10?
A 2x6 is 1½ × 5½ in, a 2x8 is 1½ × 7¼ in and a 2x10 is 1½ × 9¼ in. The thickness is always 1½ in for 2x stock. Widths up to 6 inches lose ½ inch; widths of 8 inches and up lose ¾ inch, which is why a 2x8 is 7¼ rather than 7½.
Do nominal and actual sizes apply to pressure-treated lumber?
Yes - a pressure-treated 2x4 is still 1½ × 3½ in. Treatment adds moisture and a little weight but does not change the nominal-to-actual sizing. Rough-sawn and some hardwood boards are the exception: they can be close to their full nominal size, which is why board-foot pricing uses the nominal figure.
Do I use nominal or actual size to calculate board feet?
Use the nominal size. A 2x4 is figured as 2 by 4 for board feet, not its actual 1½ × 3½, because that is the convention lumber is priced on. Enter the nominal size in the board foot calculator.