Board Foot Calculator: Lumber Volume in Seconds
Walk into a lumber yard and the price tags rarely say what a board costs. They quote a price per board foot instead, because lumber is sold by volume, not by the piece: a short, thick plank holds more wood than a long, thin one, and the yard charges for the wood itself. A board foot is the unit that volume is measured in — a piece of wood 1 foot long, 1 foot wide and 1 inch thick, which is 144 cubic inches of timber. This board foot calculator turns the thickness, width and length of any board into board feet, multiplies it across as many identical boards as you are buying, and prices the pile when you add a rate per board foot.
One note before you start: board feet are the standard lumber measure in the US and Canada. Yards in most other countries sell timber by the cubic metre or by the piece, so if you are buying outside North America, check which unit the price on the rack actually refers to.
How to calculate board feet
The formula fits on one line: board feet = thickness (in) × width (in) × length (ft) ÷ 12. Thickness and width go in as inches, length as feet, and dividing by 12 turns the result into board feet. Every measurement is the size marked on the rack — the nominal size — a point the next section explains, because it decides which numbers you should type in.
Worked example: a 2×6 that is 10 feet long. Multiply the thickness by the width, 2 × 6 = 12. Multiply by the length, 12 × 10 = 120. Divide by 12 and the board holds exactly 10 board feet. A yard charging $6 per board foot would price that single board at $60, before tax.
Board Foot Calculator
Enter the size marked on the rack — thickness and width in inches, length in feet — and the results update as you type, or press Calculate.
Formula: board feet = thickness (in) × width (in) × length (ft) ÷ 12. One board foot = 144 cubic inches of wood.
Nominal vs actual sizes
The board in your hands is smaller than the board on the label. A 2×4 leaves the sawmill at roughly 2 inches by 4 inches, but it is then dried, which shrinks it, and planed smooth on all four faces, which shaves off a little more. What reaches the rack measures 1½ × 3½ inches, and every common size shrinks by a similar margin: the bigger the board, the bigger the gap, up to about three-quarters of an inch on wide stock.
| Nominal size | Actual size |
|---|---|
| 1×2 | ¾ × 1½ in |
| 1×4 | ¾ × 3½ in |
| 1×6 | ¾ × 5½ in |
| 2×4 | 1½ × 3½ in |
| 2×6 | 1½ × 5½ in |
| 4×4 | 3½ × 3½ in |
Here is the part that catches people out: at most lumber yards, board feet are calculated from the NOMINAL size — the 2×4 is charged as a full 2 inches by 4 inches, even though you carry home 1½ by 3½. So in this calculator, enter the size the yard charges for when you are working out cost, which is the nominal size on the label. Use the actual size only for project maths — working out what a finished frame, shelf or tabletop will really measure once it is built.
Common boards
A few sizes turn up on almost every project list. For a quick check before you order, these are the board feet in the boards yards sell most:
| Board (nominal size × length) | Board feet |
|---|---|
| 1×6 × 8 ft | 4.00 bf |
| 2×4 × 8 ft | 5.33 bf |
| 2×4 × 10 ft | 6.67 bf |
| 2×6 × 8 ft | 8.00 bf |
| 1×8 × 8 ft | 5.33 bf |
Buying tips
Add 10–15% to your total before you order. Offcuts, end trims, a warped board you reject at the rack and the one cut you measure wrong all come out of the same pile, and running short mid-project means a second trip for a single board. The longer and more figured the boards, the closer to 15% you should go; for short, straight framing lumber, 10% is usually enough.
Before you pay, check whether the yard prices by nominal or actual size — most charge nominal, but it is not universal, and on a big order the difference is real money. It is also worth asking how the yard rounds: many tally board feet to the nearest quarter or charge by the bundle, either of which moves the final bill a few percent.
What to calculate next
Board feet tell you how much wood a project takes. The project calculators turn floor plans and garden layouts into the board lists, post counts and spacings you order from:
- Deck Calculator — boards, joists and posts for a deck frame and surface.
- Fence Calculator — pickets, rails and posts along any fence run.
- Square Footage Calculator — the area of any shape, before you price materials for it.
Frequently asked questions
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches of wood. Picture a board 1 foot long, 1 foot wide and 1 inch thick — that is one board foot. Any board can be measured against that block: multiply thickness in inches by width in inches by length in feet, then divide by 12.
How do I calculate board feet?
Use the formula thickness (in) × width (in) × length (ft) ÷ 12. A 1×6 board that is 8 feet long works out at 1 × 6 × 8 ÷ 12 = 4 board feet. For several identical boards, multiply the single-board figure by the quantity — the calculator above does both steps at once and can price the total.
Why is a 2×4 not 2 inches by 4 inches?
Because 2×4 is its nominal size — the rough size when it leaves the saw. The board is then dried, which shrinks it, and planed smooth, which trims it further, so the board you buy actually measures 1½ × 3½ inches. Most yards still charge board feet on the nominal size, so enter the label size when you work out cost.
How much extra lumber should I buy?
Add 10–15% to your board foot total. The extra covers offcuts, end trims, defects hiding inside a board and the occasional mis-cut. Straight, simple framing work sits near 10%; projects with long boards, angled cuts or visible grain worth matching belong nearer 15%.
Estimates only — confirm how your lumber yard counts board feet before ordering.