LUMBER REFERENCE
Nominal vs. Actual Lumber Sizes
Nominal lumber sizes are the familiar dimensions used to identify boards, such as 2x4, 2x6, and 4x4. The actual finished dimensions are smaller.
What Is the Difference?
A nominal lumber size is the traditional name used to identify a piece of dimensional lumber. An actual size is the measured finished dimension of the board after processing.
For example, a standard dry 2x4 is commonly identified as a 2x4, but its actual finished dimensions are approximately 1.5 inches × 3.5 inches.
| Nominal Size | Actual Thickness | Actual Width |
|---|---|---|
| 2x4 | 1.5 in | 3.5 in |
| 2x6 | 1.5 in | 5.5 in |
| 2x8 | 1.5 in | 7.25 in |
| 2x10 | 1.5 in | 9.25 in |
| 2x12 | 1.5 in | 11.25 in |
| 4x4 | 3.5 in | 3.5 in |
| 4x6 | 3.5 in | 5.5 in |
| 6x6 | 5.5 in | 5.5 in |
Why Is Actual Lumber Smaller?
Lumber is commonly rough-sawn before it is dried and surfaced. Planing and finishing remove material from the board, so the finished dimensions are smaller than the original nominal dimensions.
This is why a board sold as a 2x4 does not normally measure exactly 2 inches by 4 inches.
Nominal Size vs. Actual Size Example
If you are buying a 2x4 for a construction or woodworking project, the nominal size is 2x4, while the actual finished dimension is approximately 1.5 × 3.5 inches.
When calculating clearances, framing dimensions, shelf spacing, or project layouts, use the actual dimensions rather than assuming the nominal dimensions are the measured size.
Common Nominal Lumber Sizes
Frequently Asked Questions
Is a 2x4 actually 2 inches by 4 inches?
No. A standard dry 2x4 is commonly about 1.5 inches thick and 3.5 inches wide after finishing.
What does nominal lumber size mean?
Nominal size is the traditional size name used to identify dimensional lumber. It is not necessarily the final measured size.
Should I use nominal or actual dimensions for a project?
Use the actual dimensions when precise measurements, clearances, spacing, or material calculations are important.