CalcCoverageHow to calculate board feet
A board foot is a volume of lumber: a piece 1 inch thick, 12 inches wide and 1 foot long — 144 cubic inches. Hardwood and rough lumber are priced by the board foot, so this is the number that decides what your project actually costs.
Board feet = thickness (in) × width (in) × length (ft) ÷ 12
Example: a board 1 in thick, 6 in wide and 8 ft long is 1 × 6 × 8 ÷ 12 = 4 board feet. Ten of them: 40 board feet (about 0.094 cubic meters).
Nominal size vs real size
Big-box lumber is sold by its nominal name but measured by its actual size, and the difference is where board-foot math goes wrong:
| Nominal | Actual size | Board feet per foot |
|---|---|---|
| 1 × 4 | 0.75 × 3.5 in | 0.22 |
| 1 × 6 | 0.75 × 5.5 in | 0.34 |
| 2 × 4 | 1.5 × 3.5 in | 0.44 |
| 2 × 6 | 1.5 × 5.5 in | 0.69 |
| 2 × 8 | 1.5 × 7.25 in | 0.91 |
| 4 × 4 | 3.5 × 3.5 in | 1.02 |
Enter the actual dimensions in this calculator (the pre-filled hint uses the real size of a 2×4). Lumber yards selling rough hardwood usually calculate from nominal rough dimensions — check their convention before a big order.