Calculate board feet and optional cost with quantity, unit conversion, and wastage allowances.
How this is calculated
A board foot is a volume measure: 1 inch thick × 12 inches wide × 1 foot long.
board_feet_each = (thickness_in × width_in × length_ft) ÷ 12board_feet_total = board_feet_each × quantity × (1 + wastage%)boards_to_buy = ceil( quantity × (1 + wastage%) )Hardwood is sold by the board foot; dimensional softwood is usually sold by the piece; pick the matching pricing mode.
Use nominal thickness (e.g., 1″ for a "5/4" board); that is what board-foot pricing assumes.
What is a board foot?
A board foot is the volume of a piece of lumber 1″ thick × 12″ wide × 1 ft long, or 144 cubic inches. Hardwood is almost always priced this way. Dimensional softwood (2×4s, 2×6s) is priced per piece.
Should I use nominal or actual lumber dimensions?
Nominal. A "2×4" measures 1.5″ × 3.5″ actual, but board-foot pricing uses 2 × 4. Hardwood is quoted in "quarters" (4/4 = 1″, 5/4 = 1.25″) which are nominal, so use those.
How much wastage for hardwood?
10% covers most rough cuts. Bump to 15–20% when you need clear stock with no defects, when the cut list has lots of short pieces, or when you're working with figured/specialty wood that's more expensive to re-order.
Board feet for hardwood, pieces for framing
A yard that prices hardwood by the board foot is measuring volume, not length, which is why a wide thin board and a narrow thick one can ring up the same. If you are buying hardwood or checking a lumber quote, board feet is the number to understand.
A worked example
Say you need 15 walnut boards, each 4/4 (that is 1 inch thick), 6 inches wide, and 8 feet long. Board feet is thickness in inches times width in inches times length in feet, divided by 12. So each board is 1 times 6 times 8, divided by 12, which is 4 board feet. Fifteen boards comes to 60 board feet, and that is the number the yard multiplies by its per-board-foot price.
Common mistakes
- Board-footing your framing lumber. Dimensional softwood like a 2 by 4 or 2 by 6 is sold by the piece, not the board foot. Board feet is a hardwood measure.
- Using the actual dressed size instead of the nominal one. A 4/4 board is priced as 1 inch and a 5/4 as 1.25 inches, even though the planed board measures a hair less.
- Assuming a wider board always costs more. Because board feet is volume, a 1 by 12 and a 2 by 6 of the same length work out to the same board footage, so they cost the same in material.
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