What a board foot actually measures

A board foot is 144 cubic inches of wood. The classic reference piece is one inch thick, twelve inches wide, and twelve inches long. Because it is a measure of volume, thickness counts just as much as width and length: a two-inch-thick board holds twice the board footage of a one-inch board of the same face dimensions, and costs roughly twice as much even though they look identical from above.

This is why hardwood is sold by the board foot rather than the running foot. A running foot of 12-inch-wide stock and a running foot of 3-inch-wide stock are wildly different amounts of wood, but their board-foot figures capture that difference honestly.

The formula

The general formula is board feet = (thickness in inches × width in inches × length in inches) ÷ 144. When the length is in feet — which is how boards are usually described — the handy shortcut is (thickness in inches × width in inches × length in feet) ÷ 12.

Multiply the result by the number of identical boards for a total, and by the price per board foot for a cost. Our board foot calculator does all of this and accepts fractions and mixed numbers, so you can type measurements straight off the tape.

Rough vs. surfaced lumber — the common trap

Board feet are usually figured on the nominal rough thickness, quoted in quarters: 4/4 means one inch, 5/4 means 1¼ inch, 8/4 means two inches. Crucially, that figure is used even after the board has been planed (surfaced) thinner. A 4/4 board dressed to ¾ inch is still sold and calculated as one inch thick.

So always calculate and pay on the thickness you are charged for, not the final dressed thickness. Getting this wrong is the single most common board-foot mistake, and it always favours the seller.

Don't forget waste

The board-foot figure tells you the wood in the boards, not the wood your project needs. Defects, snipe, saw kerf, and the simple fact that parts rarely tile perfectly onto random-width boards all eat into the usable yield. Add 15–25% over your finished requirement, and lean toward the higher end for figured wood or projects where grain and colour must match across boards.

Frequently asked questions