The actual size of 1 x 12 lumber is around 3/4″ x 11 1/4 (19 x 304.8 mm). Definately it’s smaller than the nominal size but is the true size. However, despite the nominal size being incorrect, it is still referred to as 1-by-12 lumber in hardware stores due to the standard of measurement.
No matter what the actual or nominal size is, a 1×12 board has the same length. For example, A nominal length of 12 feet board for a 1×12 will actually be 12 feet long.
In order to find out the exact dimensions, it’s best to do some quick measurements.
1×12 lumber dimensions
| 1×12 lumber | Nominal size in inches | Actual size in inches |
| Width | 1 Width | 3/4 |
| Height | 12 length | 11 1/4 inches |
| 1×12 Lumber | Nominal size in mm | Actual size in mm |
| Width | 25.4 | 19.05 |
| Height | 285.75 | 304.8 |
Lumber has two different sizes. Actual vs Nominal. Actually, size is what the exact measurement of the lumber would be now, the Nominal size is
Why is the actual size of a 1 x 12 lumber smaller than its nominal size?
Typically, a plank is measured as it is in its original shape, but the lumber we purchase has been smoothened during the manufacturing process. This process results in the board shrinking.
Timber that is still green or fresh has a rough surface. In order to smooth out the surface of timber, it is put through a planer on both sides so that it has a uniform thickness. As thin layers of timber are sliced away during planning, its thickness shrinks, resulting in a thin edge. Timbers with smooth surfaces on all four sides generally lose thickness and width, resulting in a smaller size.
