What a board foot really is
A board foot is a measure of volume, not length or area. One board foot is 144 cubic inches — the volume of a piece one inch thick, twelve inches wide, and twelve inches long. Lumber yards use it because it lets boards of wildly different dimensions be priced on a single, comparable basis.
To find the board feet in any piece, multiply its thickness, width, and length in inches and divide by 144. The calculator does this for one board, then multiplies by your quantity for the total, and applies a price per board foot if you supply one.
Nominal versus actual size
Hardwood is often sold in quarter-inch thickness steps written as a fraction over four: 4/4 means a board milled to one inch, 8/4 means two inches, and so on. This rough or "nominal" thickness is measured before the board is surfaced.
After planing, a board is thinner than its nominal size — a nominal 4/4 board commonly finishes around 13/16 inch. Pricing is almost always based on the nominal thickness, so enter the nominal figure to match the yard's quote rather than the planed dimension.
Getting an accurate estimate
Board-foot math is unforgiving of unit mistakes, so a little care up front saves money at the till.
- Enter all three dimensions in inches; if your length is in feet, multiply it by twelve first.
- Use nominal thickness, not the planed thickness, to match how lumber is priced.
- Buy 10 to 20 percent extra to cover defects, cracks, knots, and cutting waste.
- Round-up of long boards adds up fast — confirm whether the yard sells random lengths or fixed lengths.
Pricing notes and caveats
The cost figure here is a straight multiplication of board feet by your price and is meant for quick budgeting only. Real invoices vary with species, grade, surfacing, kiln drying, and minimum-order or short-board surcharges. Softwood dimensional lumber (studs, 2x4s) is usually sold by the piece or linear foot instead of by the board foot, so this tool fits hardwood and rough lumber best.
Formula
boardFeet = (thickness(in) × width(in) × length(in)) / 144 × quantityFrequently asked questions
- Is length in inches or feet?
- This calculator uses inches for all three dimensions and divides by 144. If your length is in feet, multiply by 12 first.