Board Foot Calculator
Work out board feet, total footage, and lumber cost from thickness, width, and length for any board or order.
Hardwood dealers usually quote thickness in quarters (4/4 = 1 in, 8/4 = 2 in). This calculates rough, pre-milled dimensions, so buy 15 to 20% extra to cover material lost to jointing and planing.
How it works
A board foot is a volume measurement, not a length. One board foot is a piece of wood 1 inch thick, 12 inches wide, and 12 inches long, so the formula for any board is (thickness in inches × width in inches × length in feet) divided by 12. Lumber yards sell hardwood by the board foot because it accounts for thickness, unlike a 2x4 at the home center that's priced by the linear foot.
Worked example: a rough walnut board that's 1 inch thick, 6 inches wide, and 8 feet long comes out to (1 × 6 × 8) / 12, which is 4 board feet. Order three of those boards and you're at 12 board feet total. At $5.50 a board foot, one board runs $22, so the full order lands around $66 before tax. Enter your own numbers above and the calculator does the same math for boards of any size.
FAQ
Why do hardwood dealers talk about "quarters" instead of inches?
It's shorthand for rough thickness before milling. 4/4 (four-quarter) means 1 inch, 8/4 means 2 inches, 5/4 means 1-1/4 inches, and so on. When a price sheet lists a species as "8/4 walnut," plug in 2 for thickness and the calculator handles the rest.
Why does the calculator ask for length in feet but thickness and width in inches?
That mixed-unit setup is standard in the lumber trade and it's baked into the /12 at the end of the formula, which converts the whole calculation to cubic feet. Keep thickness and width in inches and length in feet and the math works out correctly every time.
Should I buy exactly the board footage my project needs?
No. Rough lumber is sold before it's jointed and planed flat and square, and that process removes material, plus you'll want to cut around knots, checks, and warp. Add 15 to 20% to your calculated total, more if the board has visible defects or you need to match grain across a panel.
Does this work for plywood or sheet goods?
No, this formula is for solid lumber sold by the board foot. Plywood and other sheet goods are priced per sheet, so there's no board foot math involved. If you're pricing a project that mixes solid wood and sheet goods, calculate each separately.
For more background on how lumber is sized and graded, see understanding lumber dimensions and grades, softwood vs hardwood, and how to measure and mark wood accurately.