MathBench

Board Foot Calculator

Turn a board's thickness, width, length, and quantity into board feet, and into dollars at your supplier's price per board foot.

You need

—total board feet
—board feet per piece
—estimated cost

How this calculator works

Pick the board's thickness (in the hardwood trade's quarters system or as a custom measurement), then enter width in inches, length in feet, and how many identical boards you're buying. The calculator multiplies the three dimensions into board feet per piece, scales by quantity, and prices the stack at your supplier's rate per board foot.

Buying random-width stock, where every board is different? Run each board at quantity 1 and keep a running tally. That's how the dealer's chalkboard works, and doing your own math beside theirs is the polite way to catch rounding drift.

The formula

Board feet (per board) = thickness (in) × width (in) × length (ft) ÷ 12
Total BF               = board feet × quantity
Cost                   = total BF × price per BF

One board foot is 144 cubic inches of rough lumber (1″ × 12″ × 12″). With length in inches instead of feet, divide by 144 rather than 12. Thickness uses the rough-sawn nominal size: a surfaced 4/4 board bills as a full inch even though it measures about 13/16″.

Worked example

Say you're buying ten 4/4 red oak boards, 6 inches wide and 8 feet long, at $6.00 per board foot:

  1. Per board: 1 × 6 × 8 ÷ 12 = 4 board feet
  2. Total: 4 × 10 = 40 board feet
  3. Cost: 40 × $6.00 = $240

Switch the same stack to 8/4 (2″ thick) and the total doubles to 80 BF and $480. Thickness is the quiet multiplier people forget at the lumberyard.

Assumptions & tips

  • Budget on rough sizes, build on actual. You pay for 4/4 but your finished part is ¾″. If a design needs a true 1″-thick part, you're buying 5/4 stock. Price it that way from the start.
  • Buy 15–30% over the cutlist. Knots, end checks, sapwood you don't want, and grain matching all eat stock. Leftover hardwood keeps. A mid-project trip for one more matching board usually fails.
  • Watch the width rounding. Many yards tally a 5¾″ board as 6″. On two boards it's noise. On a 200 BF order it's real money. Tally your pile before checkout.
  • Construction lumber isn't priced this way. 2×4s and other dimensional softwood sell by the piece. Board feet is the hardwood dealer's and sawmill's unit. That's where this calculator earns its keep.
  • Check the length assumption. Hardwood lengths are often sold in even feet with odd inches thrown in free: a 100½″ board bills as 8′. Ask how your yard measures before assuming.

Frequently asked questions

What do 4/4, 5/4, and 8/4 mean?

Hardwood thickness is quoted in quarters of an inch, measured on the rough-sawn board: 4/4 ("four-quarter") is 1 inch, 5/4 is 1¼, 6/4 is 1½, and 8/4 is 2 inches. After surfacing, a 4/4 board measures about 13/16 inch, but you pay board feet on the rough thickness, which is what this calculator expects.

How many board feet are in a 2×4×8?

Nominally, 2 × 4 × 8 ÷ 12 = 5.33 board feet. In practice, construction lumber like 2×4s is sold by the piece, not by board feet. Board feet are how hardwood dealers and sawmills price lumber. Use this calculator when the price tag reads per board foot.

Does board footage use nominal or actual dimensions?

Rough (nominal) dimensions. A surfaced 4/4 board that now measures 13/16 inch thick is still billed as 1 inch, and a board measured at 5¾ inches wide is often tallied as 6 by the yard. Width on random-width stock is measured to the nearest inch at the yard, small rounding that adds up on a big order, so tally your pile before the register does.

Sources

  1. The Illustrated Guide to American Hardwood Lumber Grades. American Hardwood Export Council, in collaboration with the National Hardwood Lumber Association, 2017. americanhardwood.orgGives the board-foot formula this calculator uses (width in inches × length in feet × thickness in inches ÷ 12), the quarters thickness convention where 4/4 is one inch, the rule that surfaced stock of 1½ inches and under loses 3/16 inch (so a 4/4 board finishes at 13/16) and the tally practice of rounding random widths to the nearest inch.
  2. Rules for the Measurement and Inspection of Hardwood and Cypress. National Hardwood Lumber Association. nhla.comThe rulebook that governs how hardwood is measured, graded and tallied in board feet, and the standard the conventions on this page ultimately rest on.
  3. Voluntary Product Standard PS 20-20: American Softwood Lumber Standard. U.S. Department of Commerce, National Institute of Standards and Technology, 2020. nist.govSets the nominal versus dressed sizes for construction softwood, which is the convention behind the 2×4 question in the FAQ.

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