TidyToolsWhat is a board foot?
A board foot is the standard unit for buying rough and hardwood lumber. One board foot is a piece 1 inch thick, 12 inches wide, and 12 inches long — in other words, 144 cubic inches of wood. Because boards come in all sorts of sizes, board feet give a consistent way to measure and price them by volume rather than by the piece.
The formula is simple: board feet = (thickness in inches × width in inches × length in feet) ÷ 12, multiplied by how many pieces you're buying. This calculator runs that for each board and totals it, and if you enter a price per board foot it estimates the cost too — handy at the lumber yard where prices are almost always quoted per board foot.
A worked example
A board 1 in thick, 6 in wide, and 8 ft long is (1 × 6 × 8) ÷ 12 = 4 board feet. Buy 5 of them and that's 20 board feet. At $6 per board foot, your timber comes to about $120.
Tips
- Use nominal vs actual carefully — rough lumber is measured at its full ("nominal") size; planed/surfaced boards are slightly smaller.
- Quarter system: hardwood thickness is often sold in quarters of an inch — "4/4" means 1 inch, "8/4" means 2 inches.
- Add extra for defects, cuts, and mistakes — 15–20% is a common buffer.
- Prices are per board foot, so this is the number the yard will quote against.
Frequently asked questions
How do you calculate board feet?
Multiply thickness (inches) × width (inches) × length (feet), then divide by 12. Multiply by the number of pieces for the total.
What does 4/4 lumber mean?
Hardwood thickness is sold in quarter-inches. 4/4 is 1 inch thick, 5/4 is 1.25 inches, and 8/4 is 2 inches (nominal, before surfacing).
How much extra lumber should I buy?
Add roughly 15–20% over your finished requirement to allow for cuts, defects, and mistakes.