Have you ever wondered why a 2×4 isn’t actually 2 inches wide? It’s called a 2×4 but the dimensions are 1.5” x 3.5.” You are used to “sizes” like 2×4, 2×6, 1×2, etc. but none of them really measure up to those dimensions.
Fortunately there is no vast lumber conspiracy. When first rough sawn from a log, a board is a full 2”x4”, but drying and planing reduce it to the finished 1.5×3.5 size. The cost of the original board plus machining is figured into the finished board so you really aren’t being cheated. And it certainly is a lot easier to refer to a board as a “2×4”, rather than a “1.5×3.5”.
Nominal Sizes
Softwoods, wood from coniferous trees (evergreens) like pine or cedar will typically be sold in nominal sizes. These tables show some of the most common nominal sizes with their actual measurements:
| Nominal Size | Actual Size |
| 1×1 | ¾ x ¾ |
| 1×2 | ¾ x 1½ |
| 1×3 | ¾ x 2½ |
| 1×6 | ¾ x 5¼ |
| 1×8 | ¾ x 7¼ |
| 1×10 | ¾ x 9¼ |
| 1×12 | ¾ x 11¼ |
| Nominal Size | Actual Size |
| 2×2 | 1½ x 1½ |
| 2×3 | 1½ x 2½ |
| 2×4 | 1½ x 3½ |
| 2×6 | 1½ x 5¼ |
| 2×8 | 1½ x 7¼ |
| 2×10 | 1½ x 9¼ |
| 2×12 | 1½ x 11¼ |
Quarters
Now the plot thickens…hardwoods are generally sold by “quarters” when referring to thickness. Hardwood lumber is produced from deciduous trees (a tree which drops its leaves each year). Common domestic hardwoods would be oak, maple and walnut.
In the quarter system, 4/4 (four quarters) refers to a 1” thick board. 8/4 (eight quarters) is a 2” thick board and so on. But, a 4/4 board isn’t really 1” thick – once it has been planed it will usually be about 13/16” thick. Similarly an 8/4 board will be about 1-13/16” thick.
Hardwoods are generally sold by the board foot since they come in random lengths and widths, so you need to know how many board feet you are buying. A board 12” wide x 12” long x 1” thick equals one board foot. It is easy to calculate board feet – just take the length x width x thickness in inches and divide by 144.
Knowledge is Power!
Knowing how lumber is sold and its actual dimensions will let you plan your projects accurately. You can use the true dimensions to calculate the actual amount of lumber you need to buy before you head to the store. Always lay out your plans using the actual dimensions but be sure to refer to them in nominal sizes or quarters so you sound savvy in the lumberyard.
