Lumber is sold by volume, not by the piece, and the unit of that volume in North America is the board foot. Prices on the rack are quoted per board foot, so two boards that look like cousins can cost very different amounts — and the only way to compare them, or to budget a project, is to turn each board's dimensions into board feet. This calculator does that for one board or a whole stack, and prices the stack at whatever rate your yard charges.
The board foot formula
One board foot is exactly 144 cubic inches of wood — a square foot of wood one inch thick. The formula multiplies the board's three dimensions (with length converted from feet, which is why the divisor is 12 rather than 144) and gives the volume in those units. A 2 × 4 that is 8 feet long holds 2 × 4 × 8 ÷ 12 = 5.33 board feet; a 1 × 6 of the same length holds exactly 4. Because the arithmetic is pure volume, it works for rough-sawn timber, hardwood boards and live-edge slabs alike — measure the slab at its average width if the edges wander.
Nominal sizes, actual sizes, and what you pay for
Softwood lumber is named by its size before drying and surfacing: the “2 × 4” in the rack measures about 1.5 × 3.5 inches in your hand. Yards nevertheless bill softwood board feet on the nominal dimensions — the 2 and the 4 — and that is the convention this calculator follows when you enter the sizes as sold. Hardwood is usually sold by thickness in quarters: 4/4 (“four-quarter”) is roughly 1 inch rough, 8/4 is roughly 2 inches. If your yard measures differently, enter the dimensions they bill on; the formula does not care which convention feeds it, as long as you are consistent.
Waste, warp and the extra board
Board feet measure the wood you buy, not the wood that ends up in the project. Crosscuts, defects you cut around, a board that cups on the way home — plan on 10–20% extra for straightforward work and more for projects that demand long, clear, matching boards, where selection is the real cost. Buying one board beyond the math is almost always cheaper than a second trip, and leftover hardwood keeps for the next project in a way leftover mixed concrete does not.
Worked example
The defaults describe the most bought board in the world: a 2 × 4, 8 ft long. It holds 2 × 4 × 8 ÷ 12 = 5.33 board feet. Ten of them are 53.33 board feet, and at $3.50 per board foot the stack costs about $186.67 — enter your yard's rate in the price box to see your own figure.
How to use this tool
- Enter the board's thickness and width in inches, as sold (nominal sizes for softwood).
- Enter the length in feet — for a board sold as 8 ft, that is simply 8.
- Set the number of boards if you are pricing a stack, not a single piece.
- Optionally enter the yard's price per board foot to get the stack's cost.
- Add 10–20% more boards for cuts and defects before you order.
Board feet for a whole project
To budget a deck, a workbench or a set of shelves, list every distinct part size, run each through this calculator with its quantity, and add the board-foot totals — that sum, plus waste, is the number to take to the yard. Keep the list: if one size is out of stock, substituting two narrower boards for one wide one changes the board feet very little, and you can re-run just that line rather than starting the estimate over. Yards that sell by the board foot will also often surface and straighten hardwood for a small per-board-foot fee; ask before you assume the rough price is the final price.