The formula
Board feet = thickness (in) × width (in) × length (ft) ÷ 12 1 board foot = 144 cubic inches (1 in × 12 in × 12 in)
Example: one 2 × 6 board, 8 feet long, is 2 × 6 × 8 ÷ 12 = 8 board feet. Ten 1 × 8 boards 10 feet long are 66.67 board feet.
Board feet for common lumber
| Board (nominal size) | Board feet |
|---|---|
| 2 × 4, 8 ft | 5.33 |
| 2 × 4, 10 ft | 6.67 |
| 2 × 6, 8 ft | 8 |
| 2 × 8, 10 ft | 13.33 |
| 2 × 10, 12 ft | 20 |
| 2 × 12, 16 ft | 32 |
| 4 × 4, 8 ft | 10.67 |
| 1 × 6, 8 ft | 4 |
| 1 × 12, 8 ft | 8 |
Nominal or actual size?
Dimensional softwood lumber is counted by its nominal size, so a 2 × 4 counts as 2 by 4 inches even though it measures 1½ by 3½. Hardwood is sold by thickness in quarter inches: 4/4 is 1 inch, 5/4 is 1¼ inches and 8/4 is 2 inches.
Questions
What is a board foot?
A volume of wood 1 inch thick, 12 inches wide and 12 inches long: 144 cubic inches.
How many board feet are in a 2×4×8?
5.33 board feet: 2 × 4 × 8 ÷ 12.
How many board feet are in a cubic foot?
12 board feet.