What Is a Board Foot?
A board foot is a unit of lumber volume equal to a piece measuring 1 inch thick × 12 inches wide × 12 inches long — or any combination that equals the same volume. It's the standard unit used by lumber yards, sawmills, and hardwood dealers across North America.
Board Foot Formula
Board Feet = (Thickness × Width × Length) ÷ 12
Where thickness and width are in inches, and length is in feet.
Example Calculation
A board that is 1.5" thick × 5.5" wide × 8 feet long:
(1.5 × 5.5 × 8) ÷ 12 = 66 ÷ 12 = 5.5 board feet
Common Lumber Sizes in Board Feet
| Nominal Size | Actual Size | BF per 8ft board | BF per 12ft board |
|---|---|---|---|
| 1×4 | ¾" × 3½" | 1.75 | 2.63 |
| 1×6 | ¾" × 5½" | 2.75 | 4.13 |
| 2×4 | 1½" × 3½" | 3.5 | 5.25 |
| 2×6 | 1½" × 5½" | 5.5 | 8.25 |
| 2×8 | 1½" × 7¼" | 7.25 | 10.88 |
| 2×10 | 1½" × 9¼" | 9.25 | 13.88 |
| 4×4 | 3½" × 3½" | 8.17 | 12.25 |
When Do You Need Board Feet?
- Ordering hardwood at a lumber yard (hardwood is sold by the board foot)
- Estimating lumber costs for furniture or cabinet making
- Calculating wood for flooring, decking, or siding projects
- Comparing prices between different board sizes
Pro tip: Always add 10–15% waste factor when ordering lumber for any project. Cuts, knots, and defects always reduce usable yield.