What Is a Board Foot?
The board foot sounds like a length, but it is a volume. Once you picture the 144 cubic inches it represents, lumber quotes, cut lists, and hardwood prices all start making sense.
A board foot is 144 cubic inches of lumber, the volume of a board 12 inches wide, 12 inches long, and 1 inch thick. The lumber industry prices hardwood per board foot because it normalizes boards of different sizes into one comparable unit, so a thin wide board and a thick narrow board with the same volume cost the same per unit.
The definition
A board foot is 144 cubic inches of lumber. Picture a board 12 inches wide, 12 inches long, and 1 inch thick: that is exactly one board foot. Any combination of dimensions that multiplies out to 144 cubic inches is also one board foot. A board 6 inches wide, 24 inches long, and 1 inch thick is one board foot. So is a board 12 inches wide, 6 inches long, and 2 inches thick. Volume is volume.
The standard formula expresses the same idea in the units lumber is sold in: board feet = thickness (inches) x width (inches) x length (feet) / 12. See the full walkthrough in our guide on how to calculate board feet.
Why the industry uses board feet instead of pieces or pounds
Boards come in wildly different sizes, and pricing per piece would make comparison impossible: is a $12 1x6x8 a better deal than a $20 2x8x8? Board feet reduce every board to one number, its volume, so price per board foot is an apples-to-apples unit price like price per ounce at the grocery store. Weight fails as a unit because moisture content swings it: green lumber can weigh nearly twice what the same board weighs after kiln drying, while the volume barely changes. Board feet stay stable from the sawmill to your shop.
Board feet vs linear feet
Linear feet measure length only: a 10-foot board is 10 linear feet no matter how wide or thick it is. Board feet measure volume, so width and thickness matter. A 10-foot 2x4 is 6.67 board feet; a 10-foot 2x12 is 20 board feet. Home centers price dimensional lumber per piece or per linear foot because every 2x4x8 is identical, but hardwood yards, where every board differs, price per board foot.
Board feet vs square feet
Square feet measure area, which is what you plan in when you cover a surface like a floor or deck. Board feet measure volume. The two are related through thickness: square feet = board feet / thickness in inches. For 1-inch stock they are numerically equal, which is a handy shortcut, but a 2-inch board holds twice the board feet per square foot. Our board feet to square feet guide works through the conversions.
What a board foot looks like in real boards
- One 2x4, 8 feet long: 5.33 board feet. The most common board in America is five and a third board feet.
- One 1x6, 8 feet long: 4 board feet, exactly.
- One 4x4 post, 8 feet long: 10.67 board feet.
- One 2x6, 12 feet long: 12 board feet, exactly.
- Ten 1x8 boards, 10 feet long: 66.7 board feet, a small furniture project's worth.
The nominal-size wrinkle
Here is the part that confuses beginners: board feet are calculated from nominal dimensions, not actual ones. A 2x4 is nominally 2 by 4 inches but actually measures 1.5 by 3.5 inches after the mill dries and planes it. The industry still counts it as a 2x4 for board footage, because the price reflects the rough stock the mill started with. So the 5.33 board feet in an 8-foot 2x4 is measured on the nominal 2 by 4, not the actual 1.5 by 3.5. This is standard practice at every lumberyard, not a trick, and it is why your computed numbers match the yard's quote when you use nominal sizes.
Where you will meet board feet in the wild
Hardwood lumberyards price nearly everything per board foot and quote projects that way. Sawmills selling rough-sawn stock quote per board foot, often with a minimum. Log buyers estimate board feet inside a standing tree or log with log scales like the Doyle rule, which approximates how many board feet a sawmill will recover. Woodworkers total board feet on cut lists to budget projects before buying a single board. The unit follows the wood from forest to finished furniture.
A 30-second history
The board foot dates to an era when nearly all lumber was rough-sawn to full nominal size and sold by volume to shipbuilders, coopers, and carpenters. A 12x12x1 inch block was a natural unit: easy to visualize, easy to tally on a board-by-board basis. Sawn lumber got thinner with modern planing, which is why a nominal 1-inch board is actually 3/4 inch today, but the unit survived because nothing better replaced it. Every alternative, weight, piece count, linear feet, breaks down the moment boards vary in size, which they always do in hardwood.
Skip the arithmetic
Now that the definition clicks, try it on real boards: our free calculator computes board feet for any board and totals a whole project cut list.
Board foot definition questions
What is a board foot in simple terms?
A board foot is 144 cubic inches of lumber, the volume of a board 12 inches wide, 12 inches long, and 1 inch thick. Any set of dimensions that multiplies to 144 cubic inches is one board foot.
How big is a board foot visually?
Picture a 12-inch square tile that is 1 inch thick. That is one board foot. A standard 2x4 that is 8 feet long contains 5.33 of those tiles worth of wood.
Why is lumber sold by the board foot?
Because boards come in different sizes, and the board foot reduces every board to one comparable number, its volume. That makes price per board foot a true unit price, like price per ounce. Weight does not work because moisture content changes it.
Is a board foot the same as a linear foot?
No. A linear foot measures length only; a board foot measures volume. A 10-foot 2x4 is 10 linear feet but 6.67 board feet, while a 10-foot 2x12 is 10 linear feet but 20 board feet.
Are board feet based on nominal or actual size?
Nominal. A 2x4 counts as 2 by 4 inches for board footage even though it actually measures 1.5 by 3.5 inches. The price reflects the rough stock the mill started with, and this is standard practice at every lumberyard.