Board Foot Calculator

How to calculate board feet

A board foot is a piece of wood 1 foot wide, 1 foot long and 1 inch thick — 144 cubic inches. For any board:

board feet = thickness (in) × width (in) × length (ft) ÷ 12

Worked example. Ten 2×4s, 8 ft long, and four 2×6s, 12 ft long:

• 2×4 × 8 ft: 2 × 4 × 8 ÷ 12 = 5.33 bd ft each × 10 = 53.33 bd ft
• 2×6 × 12 ft: 2 × 6 × 12 ÷ 12 = 12 bd ft each × 4 = 48 bd ft
• Total: 101.33 board feet, 14 pieces, 128 linear feet

That is the calculator’s starting list. Change it to your own: pick a nominal size, set the length and the number of pieces, and add a line for each size you are buying.

Nominal or actual size?

Lumber is named by its nominal size, which is larger than the wood you can measure. The American Softwood Lumber Standard (PS 20, published by NIST) sets the dressed sizes — and also says that board feet are counted with the nominal size: “multiplying the nominal thickness in inches … by the nominal width in feet by the length in feet.”

So use the nominal size when you compare prices or check an invoice; use the actual size when you design — a wall of 2×4 studs is 3½ inches thick, not 4.

Hardwood: thickness in quarters

Hardwood dealers sell rough lumber by board feet, with the thickness in quarters of an inch:

Hardwood boards come in random widths, so measure each board’s width (or the total width of a stack of the same length) and enter it with the thickness chosen from the list. Rough boards lose some thickness when you plane them; the board feet you pay for are counted on the rough size.

Pricing: per piece, per board foot or per linear foot

Home centers price construction lumber per piece; lumberyards often quote per board foot or per thousand board feet (MBF); trim and molding are sold per linear foot. Each line in the calculator can use its own basis, so you can compare a lumberyard quote with store prices for the same list. To convert, a price per board foot × board feet per piece = price per piece.

Extra for waste and defects

Some boards will have knots, splits or wane where you need a clean cut, and offcuts are rarely long enough to reuse. Add a percentage under Extra for waste & defects to raise both the board feet and the cost. How much depends on the grade and the project — a small allowance for construction framing, more for furniture where you cut around defects.

Planning the rest of the job? The concrete calculator covers deck footings and post holes, the square footage calculator measures a deck or a floor, and the paint calculator works out the finish.