A 2×4 does not actually measure 2 by 4 inches. A standard 2×4 is 1.5 inches by 3.5 inches. The “2×4” is the nominal (rough) size before the board is dried and planed smooth.
| Nominal | Actual size |
|---|---|
| 2×4 | 1-1/2 x 3-1/2 in |
| 2×6 | 1-1/2 x 5-1/2 in |
| 2×8 | 1-1/2 x 7-1/4 in |
| 2×10 | 1-1/2 x 9-1/4 in |
| 2×12 | 1-1/2 x 11-1/4 in |
Where the size goes. The board starts at the full nominal size when rough-sawn, then loses material when it is surfaced smooth and dried. Boards 8 in and wider lose 3/4 in instead of 1/2 in.
FAQ
Why is a 2×4 not actually 2 inches by 4 inches? The nominal size refers to the rough-cut dimension before the lumber is dried and planed smooth, a process that removes roughly 1/2 inch from each dimension, leaving the actual finished size at about 1.5 by 3.5 inches.
See the full Lumber Dimensions Chart and Plywood Sizes Chart.