Board foot calculator

What a board foot is

A board foot is the standard volume unit for lumber: 144 cubic inches of wood, the volume of a board one foot square and one inch thick. Lumber is priced per board foot because boards come in every combination of thickness, width, and length. A volume unit lets a supplier put one price on all of them.

The formula

Board feet = thickness (inches) × width (inches) × length (feet) ÷ 12. If you measure everything in inches, divide by 144 instead. Worked example: a board 1.25″ thick, 10″ wide, and 8′ long is 1.25 × 10 × 8 ÷ 12 = 8.33 BF. Five of them at 4.15 dollars per board foot cost 8.33 × 5 × 4.15 ≈ 172.92 dollars.

The convention that trips everyone: nominal vs actual

Softwood dimensional lumber is calculated with nominal dimensions. A 2×4 actually measures 1½″ × 3½″ after drying and surfacing, but a 2×4×8′ is still counted as 2 × 4 × 8 ÷ 12 = 5.33 board feet. The industry sells the nominal size; the calculator's dimensional mode does the same and shows the actual size beside it.

Hardwood works differently: it is sold by rough quarter thickness: 4/4 ("four-quarter") is 1″, 5/4 is 1.25″, 6/4 is 1.5″, 8/4 is 2″, 12/4 is 3″. You pay for the rough-sawn thickness even when the board has been surfaced thinner. The hardwood mode uses the quarter system and carries retail price presets per species you can overwrite with your supplier's number.

Board feet, linear feet, and square feet

A linear foot measures length only, which is useful once the cross-section is fixed. For any nominal size the conversion is BF per LF = (nominal thickness × nominal width) ÷ 12, so a 2×4 is 0.667 BF per linear foot, a 2×6 is exactly 1, and a 2×12 is 2. A square foot measures area; for sheet goods the bridge is BF = square feet × thickness in inches, which is why a 3/4″ 4×8 plywood sheet (32 SF) works out to 24 BF.

Waste is part of the order, not an afterthought

Net board feet from the math is not what you order. Framing typically carries 10–15 percent waste, trim about 10, decking 5–10 (add roughly 10 points for diagonal layouts), and hardwood for furniture or millwork 15–30 percent, because grain matching and defect cutting consume stock. The waste selector applies the factor to the whole order; for grade-sensitive hardwood work, 30 percent is the safe default.

From lumber counts to a priced bid

A board-foot total is one line of an estimate. The framing package behind it (studs, plates, headers, sheathing) comes off the drawings, and that takeoff is where estimates win or lose. Ruh reads the plan set, counts the framing package, and drafts the priced estimate against your own price book, so the lumber line is traceable to the sheet it came from. See how it works on the framing estimating software page, or the material takeoff guide for the manual method.