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Board foot calculator
Hardwood is sold by the board foot. Enter the rough size of each board, how many you need and a waste allowance to see what to buy and roughly what it costs.
How to use this calculator
A board foot is a volume: a piece 1 inch thick, 12 inches wide and 12 inches long, or 144 cubic inches. The calculator multiplies thickness in inches by width in inches by length in feet and divides by 12. A board 1 inch thick, 6 inches wide and 8 feet long is 1 × 6 × 8 ÷ 12 = 4 board feet. In metric mode it converts millimeters and meters to inches and feet first, then also shows the volume in cubic meters (1 board foot is about 0.00236 m³).
Hardwood yards price rough-sawn lumber by the board foot and describe thickness in quarters of an inch: 4/4 is 1 inch, 8/4 is 2 inches. Use that rough thickness here, because it is what you pay for, even though the board ends up thinner after planing. Width and length are often measured to the nearest inch or half foot, and yards may round differently, so the total on your receipt can differ a little.
The waste allowance covers knots, checks at the ends, snipe, defects you cut around and the offcuts left over when your parts don't divide neatly into the boards. The 20% default is a planning assumption, not a rule: clear, straight stock and a simple cut list need less, while figured boards, matched grain and short parts need more. If you enter a price per board foot from your yard, the calculator multiplies it by the board feet to buy. That is the lumber cost only, before milling, finishing and labor.
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Questions about this calculator
How many board feet are in a 2×4?
Board feet use the nominal size for softwood dimensional lumber, so an 8-foot 2×4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet, even though the actual board measures about 1.5 × 3.5 inches. Most softwood framing lumber is sold by the piece anyway.
Why does a woodworker quote more board feet than the finished piece contains?
Because rough boards lose thickness and width when they are flattened and planed, and parts are cut around defects. The lumber bought is always more than the wood left in the finished piece.