Lumber Sizes
Introduction
Lumber for rough carpentry is referred to by its nominal dimension size, such as 2 x 4 (two by four). This 2 x 4 refers to 2” x 4” for the dimension the wood is milled to, however, after drying the wood shrinks as moisture evaporates and its dimension becomes less. A milled 2 x 4 piece of wood ends up being about 1-1/2” x 3-1/2”. Note that all construction grade wood dries at fairly consistent rates regardless of size, so 1” depth will generally reduce to 3/4".
- This rate of reduction is not a set percentage, but more consistent generally in reduction size. This is why 4” reduces 1/2" along with 2” reducing a similar 1/2".
Note that there are technical trade differences/definitions in the usage of the words: lumber, boards, timber. However, in our experience, these differences are so nuanced that unless speaking directly with a mill or defining them in your specifications, they can get easily interchanged.
- To learn more about those; visit our hardwood and softwood page.
Nominal vs Actual
| Nominal | Actual (inch) | Actual (mm) |
| 1 x 1 | 3/4 x 3/4 | 19.05 x 19.05 |
| 1 x 2 | 3/4 x 1-1/2 | 19.05 x 38.10 |
| 1 x 3 | 3/4 x 2-1/2 | 19.05 x 63.50 |
| 1 x 4 | 3/4 x 3-1/2 | 19.05 x 88.90 |
| 1 x 5 | 3/4 x 4-1/2 | 19.05 x 114.30 |
| 1 x 6 | 3/4 x 5-1/2 | 19.05 x 139.70 |
| 2 x 2 | 1-1/2 x 1-1/2 | 38.10 x 38.10 |
| 2 x 3 | 1-1/2 x 2-1/2 | 38.10 x 63.50 |
| 2 x 4 | 1-1/2 x 3-1/2 | 38.10 x 88.90 |
| 2 x 6 | 1-1/2 x 5-1/2 | 38.10 x 139.70 |
| 2 x 8 | 1-1/2 x 7-1/4 | 38.10 x 184.15 |
| 2 x 10 | 1-1/2 x 9-1/4 | 38.10 x 234.95 |
| 2 x 12 | 1-1/2 x 11-1/4 | 38.10 x 285.75 |
| 4 x 4 | 3-1/2 x 3-1/2 | 88.90 x 88.90 |
| 6 x 6 | 5-1/2 x 5-1/2 | 139.70 x 139.70 |
Nominal: Common shorthand size for a piece of wood (2 x 4) - typically immediately after milling.
Actual: Actual ‘real’ dimension of the piece of wood (1-1/2” x 3-1/2”)
Not all wood sizes are available in all species of wood. You can of course custom order ‘anything’... but if specifying or construction using ‘off the shelf’ materials, you may have trouble finding certain sizes, especially at home improvement stores (Menards, Home Depot, Lowes)