Volume formula
Use inches for thickness and width, feet for length
board feet = quantity × thickness (in) × width (in) × length (ft) ÷ 12
One board foot represents a volume 1 inch thick, 12 inches wide and 1 foot long. The formula works for other dimension combinations because it converts their volume into that same unit.
Worked examples
Check the units before multiplying
A 1 × 12 in board that is 8 ft long contains 8 board feet: 1 × 12 × 8 ÷ 12.
Ten entered 2 × 8 in × 8 ft boards contain about 106.7 board feet. A user-selected 10% allowance produces 117.33 board feet, which RightQty rounds upward to 117.4 board feet.
Billing dimensions
Nominal, rough and surfaced dimensions can differ
Use the dimensions the seller uses for the board-foot transaction. A nominal name may not equal the measured surfaced size, and a price per board foot may follow established trade dimensions. Confirm before treating a calculation as an invoice quantity.
Board Foot Calculator answers a volume question. Lumber Calculator answers a different purchasing question: how many whole stock boards are required from a piece count or linear-length demand.
Board-foot volume does not determine an efficient cut list, account for kerf or prove that the available stock lengths fit the project.
Sources
References and project authority
These references support the stated measurement convention or planning boundary. Product instructions, the approved design, and local requirements take priority for the actual project.
- US Forest Service board-foot definition defines the 12 × 12 × 1 in volume convention used by the formula.