Lumber is sold by nominal size, which is a name, not a measurement. A board called two-by-four is smaller in real life because drying and surfacing remove wood. To plan a project, always measure the actual board with a tape and not rely on the label.
Nominal Versus Actual
The nominal size reflects the rough-cut board before drying and planing. Once the wood is dried and surfaced, it ends up thinner and narrower. Many yards in North America follow similar conventions, but the exact numbers can vary, so check the maker’s or yard’s chart.
| Nominal name | Typical actual size |
|---|---|
| 1 x 4 | about 3/4 in by 3-1/2 in |
| 1 x 6 | about 3/4 in by 5-1/2 in |
| 2 x 4 | about 1-1/2 in by 3-1/2 in |
| 2 x 6 | about 1-1/2 in by 5-1/2 in |
These are common figures, not promises. Confirm with a tape on the actual stock.
Reading the Rest of the Label
- Length: usually stated in feet, and the real board may be slightly longer.
- Species or grade: tells you the wood type and the quality class.
- Rough or surfaced: rough stock has a sawn texture and is closer to nominal size; surfaced has been planed smooth.
- Dry condition: abbreviations may show how well it was dried.
- Hardwood: often sold by thickness in quarters of an inch, such as 4/4 for about one inch rough.
Steps for Planning with Real Sizes
- Write your project plan with the actual finished dimensions you need.
- Measure a sample of each board you are buying, because sizes can vary from board to board.
- Add extra length for trimming ends and for saw cuts.
- Check width after planing and jointing if you will remove more wood.
- Recalculate joint layouts based on the real thickness.
Tools Worth Having
A tape measure, a combination square, and calipers or a thickness gauge are enough. Use the same tool for all measurements so errors stay consistent.
A Worked Example
Say your plan calls for a shelf side that is one inch thick and five inches wide. A nominal 1 x 6 board has an actual width of roughly five and a half inches, so it already covers the need with a little left to trim. If you had bought a 1 x 4 instead, its width would fall short. Writing the real dimensions beside each label on your cut list prevents this kind of surprise at the lumber rack.
FAQ
Why is a two-by-four not two inches by four inches?
Because the name comes from the board’s rough size, before drying and planing reduce it.
Is hardwood sized the same way?
No. Hardwood is commonly described by quarter-inch thickness and sold by volume.
The Short Version
Treat the label as a name, measure real boards, and build your plan from those numbers. Allow extra length for cuts.