Lumber Dimensions
Learn the difference between nominal lumber sizes and the actual finished dimensions of common boards and posts.
Common Lumber Dimensions
| Nominal Size | Actual Thickness | Actual Width |
|---|---|---|
| 2x2 | 1.5 in | 1.5 in |
| 2x3 | 1.5 in | 2.5 in |
| 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 |
What Are Lumber Dimensions?
Lumber dimensions describe the thickness and width of a board or post. Lumber sold in the United States is commonly identified using nominal dimensions, such as 2x4 or 4x4.
The actual finished dimensions are normally smaller than the nominal dimensions because lumber is dried and surfaced during processing.
Nominal vs. Actual Dimensions
For example, a nominal 2x4 does not normally measure exactly 2 inches by 4 inches. A commonly sold dry 2x4 has an actual finished size of approximately 1.5 × 3.5 inches.
Similarly, a nominal 2x8 is commonly about 1.5 × 7.25 inches after finishing.
Actual dimensions may vary depending on the product, lumber grade, moisture condition, manufacturer, and applicable standards.
Why Actual Dimensions Matter
Actual dimensions are important when designing, measuring, cutting, framing, building furniture, or determining whether a piece of lumber will fit a specific space.
When a project requires precise measurements, use the actual dimensions of the specific lumber product rather than relying only on its nominal size.