A 2×8 piece of lumber is actually 1 ½ x 7 ½ inches (38 x 203 mm) smaller than advertised at hardware stores. It is because hardware stores sell lumber that is already planned. Measurements of lumber are taken when it is freshly cut. Even though lumber 2-by-8 dimensions have decreased to 1 ½ x 7 ½, sellers still refer to them as their original measurements.
To ensure that you get 2×8 lumber that’s the right size for your project, measure it carefully before buying it at the hardware store.
2×8 lumber Length
There is no difference in the length of a 2×8 board whether it is nominal or actual.
A 2×8 will have an actual length of 6 feet if its nominal length is 6 feet. The length of a nominally lengthened board of 12 feet will actually be 12 feet.
2×8 lumber dimensions
| 2×8 lumber | Nominal size in inches | Actual size in inches |
| 2 | 1 ½ | |
| 6 | 5 ½ |
| 2×8 Lumber | Nominal size in mm | Actual size in mm |
| 50.8 | 38 | |
| 152.4 | 76.2 mm |
Why is the actual size of a 2×8 lumber smaller than its nominal size?
To create a uniform thickness, the surface of the wood is smoothed throughout the planning process. During planning, thin layers of timber are sliced off from each side of the timber, causing its thickness to shrink. The result is that timbers with four-sided smooth surfaces lose both thickness and width, reducing their actual dimensions.
