A 2×4 actually measures 1½ × 3½ inches, or 38 × 89 mm; a 2×6 is 1½ × 5½ inches, 38 × 140 mm.
| Nominal | Actual thickness (in) | Actual width (in) | Thickness (mm) | Width (mm) | Board feet per linear foot |
|---|---|---|---|---|---|
| 1 × 2 | 0.75 | 1.50 | 19 | 38 | 0.17 |
| 1 × 3 | 0.75 | 2.50 | 19 | 64 | 0.25 |
| 1 × 4 | 0.75 | 3.50 | 19 | 89 | 0.33 |
| 1 × 6 | 0.75 | 5.50 | 19 | 140 | 0.50 |
| 1 × 8 | 0.75 | 7.25 | 19 | 184 | 0.67 |
| 1 × 10 | 0.75 | 9.25 | 19 | 235 | 0.83 |
| 1 × 12 | 0.75 | 11.25 | 19 | 286 | 1.00 |
| 2 × 2 | 1.50 | 1.50 | 38 | 38 | 0.33 |
| 2 × 3 | 1.50 | 2.50 | 38 | 64 | 0.50 |
| 2 × 4 | 1.50 | 3.50 | 38 | 89 | 0.67 |
| 2 × 6 | 1.50 | 5.50 | 38 | 140 | 1.00 |
| 2 × 8 | 1.50 | 7.25 | 38 | 184 | 1.33 |
| 2 × 10 | 1.50 | 9.25 | 38 | 235 | 1.67 |
| 2 × 12 | 1.50 | 11.25 | 38 | 286 | 2.00 |
| 4 × 4 | 3.50 | 3.50 | 89 | 89 | 1.33 |
| 4 × 6 | 3.50 | 5.50 | 89 | 140 | 2.00 |
| 6 × 6 | 5.50 | 5.50 | 140 | 140 | 3.00 |
How it is computed
The nominal size is the rough-sawn size before drying and planing. Dry dressed sizes follow the American Softwood Lumber Standard: ¾ in for 1-by stock, 1½ in for 2-by, then ½ in less up to 6 in wide and ¾ in less above. Millimetres = inches × 25.4; board feet use the nominal size: thickness × width × 12 ÷ 144.
FAQ
Why is a 2×4 not 2 by 4 inches?+
It is sawn close to 2 × 4 in, then shrinks as it dries and loses wood when planed smooth.
Are board feet based on the nominal or the actual size?+
On the nominal size, by trade convention. That is why the table uses 2 × 4 for a 2×4.