How to Calculate Board Feet for Lumber Projects

A board foot is a unit of volume, not area or length. One board foot equals 144 cubic inches, which is the amount of wood in a piece that is 1 inch thick, 12 inches wide, and 12 inches long. Because it measures volume, a board foot can take many shapes: a 1 by 12 that is a foot long and a 2 by 6 that is a foot long both contain exactly one board foot.

Hardwood lumber is almost always sold by the board foot rather than by the linear foot, which is why the same plank can cost very different amounts depending on its thickness and width. Softwood dimensional lumber, by contrast, is usually priced per piece or per linear foot, so the board foot matters most when you are buying oak, walnut, maple, cherry, and other hardwoods from a specialty supplier.

The core formula is thickness in inches times width in inches times length in inches, all divided by 144. If your length is already in feet, a simpler version is thickness in inches times width in inches times length in feet, divided by 12. Both give the same answer because 12 inches of length is folded into the divisor.

Hardwood dealers describe thickness in quarters of an inch. A board marked 4/4 (spoken as four-quarter) is nominally 1 inch thick, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. This matters because board footage is calculated from the rough, unsurfaced thickness. A 4/4 board that has been planed smooth may only measure about 13/16 of an inch, yet you still pay for the full 4/4 because that is how much raw material the mill cut.

Rough lumber is measured before it is surfaced, so its stated dimensions reflect more wood than you will see in the finished board. Width is often measured to the nearest full or half inch on rough stock, and thickness follows the quarters system. Knowing this prevents sticker shock: you are paying for the log volume the mill removed, not the trimmed piece on your bench.

When you plan a project, add extra board footage for waste. Ripping, jointing, planing, and cutting around defects such as knots and checks typically consumes 15 to 30 percent more material than your finished part list suggests. Buying a little extra up front is usually cheaper than a second trip for wood from a different batch that may not match in color or grain.

The calculator runs entirely in your browser, so nothing you enter is uploaded anywhere. Enter thickness in quarters or inches, the width, and the length, add a price per board foot if you want a running total, and it does the volume math and the cost for you.

The most frequent error is mixing units, such as entering length in feet while the tool expects inches, which inflates or deflates the total by a factor of twelve. Always confirm which unit each field wants before trusting the number.

Another mistake is calculating from the planed thickness instead of the nominal rough thickness. If a supplier sells you 4/4 stock, calculate at 1 inch even after it has been surfaced thinner, because that is the basis for their price. Finally, remember that board feet describe volume only. Two boards with identical board footage can still differ in usable width, so check that the actual dimensions fit your parts before you buy.