Board Foot Calculator

Enter thickness and width in inches, length in feet, and quantity to get board feet per piece and in total — plus the cost if you add a price per board foot. Hardwood is sold this way; here's how the math works.

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How board feet work

A board foot is the lumber trade's unit of volume: 144 cubic inches, the size of a board 1 inch thick, 12 inches wide, and 12 inches long. Hardwood comes off the sawmill in random widths and lengths, so it can't be priced per stick the way a bundle of identical 2×4s can — instead the dealer tallies the volume of wood in each board and charges by the board foot. Once you can compute it yourself, you can sanity-check a lumberyard invoice and compare a $6/bd ft walnut quote against a $12/bd ft one on equal footing.

One trade convention to know: hardwood thickness is quoted in quarters of an inch of rough thickness. 4/4 ("four-quarter") is 1 inch, 5/4 is 1¼, 6/4 is 1½, and 8/4 is 2 inches. When a dealer says "eight-quarter walnut," enter 2 in the thickness box.

The formula

board feet = (thicknessin × widthin × lengthft) ÷ 12 × quantity

Thickness and width are in inches, length is in feet — that mixed-unit shortcut is why the divisor is 12 rather than 144. If you'd rather keep everything in inches, multiply the three dimensions and divide by 144; the answer is identical.

Worked example

You order 10 pieces of 8/4 stock, 6 inches wide and 10 feet long. 8/4 means 2 inches thick, so each piece is 2 × 6 × 10 ÷ 12 = 10 board feet, and the order totals 100 board feet. At $6.50 per board foot, that's $650.00 of lumber — before the dealer's surfacing charge, if you have them plane it.

The nominal-size trap (and why it isn't a scam)

Here's the part that surprises people: board feet are tallied on nominal (rough-sawn) dimensions, not actual ones. A "2×4" actually measures 1.5 × 3.5 inches, and a 4/4 hardwood board surfaced on two sides comes to you about 13/16 inch thick — yet both are counted at their full nominal size. The reason is honest enough: the mill sawed a full-size board, and the material lost to drying shrinkage and planing was real wood that passed through the saw. The convention only becomes a trap when you mix up your two sets of math. Budget with nominal dimensions, build with actual ones. If your project needs a finished 1-inch-thick panel, 4/4 stock won't get you there after flattening — you buy 5/4 and plane down, and you pay for the full 5/4. Seasoned woodworkers also add 15-30% extra board footage for defects, grain matching, and mistakes; rough lumber is not sold defect-free.

Frequently asked questions

How do you calculate board feet?

Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2-inch-thick, 6-inch-wide, 10-foot board is 2 × 6 × 10 ÷ 12 = 10 board feet. If you have the length in inches instead, multiply all three inch dimensions and divide by 144.

How many board feet are in a 2x4x8?

Using nominal dimensions, 2 × 4 × 8 ÷ 12 = 5.33 board feet. The actual milled size of a 2×4 is only 1.5 × 3.5 inches, but board-foot tallies for dimensional and rough lumber use the nominal size — you pay for the wood the board started as, not what's left after planing.

What does 4/4 lumber mean?

Hardwood dealers state rough thickness in quarters of an inch: 4/4 ("four-quarter") is 1 inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. A board sold as 4/4 that has been surfaced on two sides will actually measure about 13/16 inch, but it is still tallied and priced as 4/4.

Do you use nominal or actual dimensions to calculate board feet?

Nominal (rough) dimensions. The board-foot measure is taken from the lumber as it was sawn, before surfacing removed material, so an 8/4 board planed down to 1.75 inches is still 8/4 for pricing. That's the industry convention, not a scam — but it does mean your project math should use actual dimensions while your budget math uses nominal.

What is the difference between a board foot and a linear foot?

A board foot measures volume — 144 cubic inches, the size of a 1-inch × 12-inch × 12-inch piece. A linear foot measures only length along the board, regardless of its width or thickness. Hardwood is priced per board foot because boards come in random widths; trim and dimensional lumber are often priced per linear foot because their cross-section is fixed.

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