Nominal vs actual lumber sizes
Softwood dimension lumber is named by its nominal size, the rough size before drying and planing. What you take home is smaller. These are the dry, surfaced sizes set by the American Softwood Lumber Standard; the last column is the board feet a lumberyard counts per linear foot, which is figured on the nominal size.
| Nominal | Actual size | Actual (metric) | Board feet per linear foot |
|---|---|---|---|
| 1×2 | ¾ × 1 ½ in | 19 × 38 mm | 0.167 |
| 1×3 | ¾ × 2 ½ in | 19 × 64 mm | 0.25 |
| 1×4 | ¾ × 3 ½ in | 19 × 89 mm | 0.333 |
| 1×6 | ¾ × 5 ½ in | 19 × 140 mm | 0.5 |
| 1×8 | ¾ × 7 ¼ in | 19 × 184 mm | 0.667 |
| 1×10 | ¾ × 9 ¼ in | 19 × 235 mm | 0.833 |
| 1×12 | ¾ × 11 ¼ in | 19 × 286 mm | 1 |
| 2×2 | 1 ½ × 1 ½ in | 38 × 38 mm | 0.333 |
| 2×3 | 1 ½ × 2 ½ in | 38 × 64 mm | 0.5 |
| 2×4 | 1 ½ × 3 ½ in | 38 × 89 mm | 0.667 |
| 2×6 | 1 ½ × 5 ½ in | 38 × 140 mm | 1 |
| 2×8 | 1 ½ × 7 ¼ in | 38 × 184 mm | 1.333 |
| 2×10 | 1 ½ × 9 ¼ in | 38 × 235 mm | 1.667 |
| 2×12 | 1 ½ × 11 ¼ in | 38 × 286 mm | 2 |
| 4×4 | 3 ½ × 3 ½ in | 89 × 89 mm | 1.333 |
| 4×6 | 3 ½ × 5 ½ in | 89 × 140 mm | 2 |
| 6×6 | 5 ½ × 5 ½ in | 140 × 140 mm | 3 |
The pattern: from 2 to 6 inches nominal, subtract ½ inch; from 8 inches up, subtract ¾ inch; 1-by boards are ¾ inch thick.
How hardwood is sold
Hardwood is sold by the board foot, with thickness in quarters of an inch: 4/4 is 1 inch rough, 5/4 is 1 ¼, 6/4 is 1 ½ and 8/4 is 2 inches. Board feet are figured on that rough thickness even when the yard planes the board for you, and widths are usually random. Hardwood sold at home centers is often already surfaced to softwood-style sizes, such as a ¾ × 5 ½ inch "1×6", and priced by the piece or the linear foot.
Which calculator do you need?
The board foot calculator totals a whole lumber list: add a line for each thickness, width and length, set a waste allowance and a price, and it gives the board feet to buy and the cost, in cubic meters too if you work in metric.