US Wood Sizes
Dimensional Lumber
Most wood lumber (or “timber” in British usage) used in the US is specified by the width and height in inches, and the length in feet. The most common example, is a “two by four” (written “2×4”), meaning it is 2 inches by 4 inches (51mm by 102mm), and commonly sold in an 8 foot (2.44m) length, or in increments of 2 feet (0.61m) for longer lengths.
Except that it isn’t really 2 inches by 4 inches: that is the “rough cut” size before it gets smoothed or “finished”. Finished sizes have shrunk over the years, and as of 1961 the actual sizes for softwood (such as pine and fir) are:
| Nominal size (inches) | Finished Size (inches) | Finished Size (mm) | comments |
| 1 | 0.75 | 19 | |
| 2 | 1.5 | 38 | |
| 4 | 3.5 | 89 | |
| 6 | 5.5 | 140 | |
| 8 | 7.25 | 184 | Except that an 8×8 is 7.5 inches (191mm) on a side. |
| 12 | 11.25 | 286 |
Hardwoods like maple and oak are more often cut to the specified size. Wood dowels, which are often (but not always) made of hardwood, are specified to the exact diameter so that it will fit in a hole of the specified size.
Plywood Sheets
Sizes for engineered wood (such as sheets of plywood) are closer to the nominal thickness, though it will be reduce somewhat if one or both sides is finished. Standard sheet size is 4 feet ( 122cm ) by 8 feet ( 244cm ), and antenna projects using plywood may sometimes be optimized to make maximum use of such a size.