Board Foot Calculator
Work out how many board feet are in a piece of lumber, how much a whole order comes to, and what it will cost. Enter the rough dimensions and quantity — the result updates as you type, in metric or imperial.
Calculator
The formula uses feet — check this matches what you typed.
10% for clean stock, 20-30% for rough-sawn.
Applied to the waste-inclusive total.
Result
Total board feet (with waste)
36.13 bf
3.927 bf per piece × 8
Board feet describe volume, not what a mill will actually charge you. Yards price by species, grade, thickness and figure, and many sell short lengths and narrow boards at a premium. Treat the cost figure as a budgeting estimate, not a quote.
What a board foot actually is
A board foot is a unit of volume: a piece one inch thick, twelve inches wide and one foot long. That is 144 cubic inches. It is not a measure of length or of surface area, which is why two boards with completely different shapes can contain the same number of board feet.
The unit is imperial by definition, so there is no separate metric formula. When you enter millimetres this calculator converts to inches and feet and runs the same expression — a "metric board foot" is not a thing that exists in the timber trade.
The formula, and why the twelve is there
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12.
The division by twelve is a unit reconciliation, not a fudge factor. Multiplying two inch measurements by a foot measurement gives you inch²·feet; since twelve inches make a foot, dividing by twelve converts that into cubic feet expressed in the trade's preferred unit. If you prefer to work entirely in inches, the equivalent is thickness × width × length-in-inches ÷ 144.
Quantity multiplies the per-piece figure. Waste is applied last, on the total, because an allowance is about the order as a whole rather than about any individual board.
Worked example
You need eight pieces of 8/4 walnut, 6 inches wide and 6 feet long, for a table base.
Per piece: (2 × 6 × 6) ÷ 12 = 6 board feet. Eight pieces: 48 board feet. Add a 15% waste allowance for defects and trimming and you should order about 55.2 board feet. At $12 per board foot that is roughly $663.
Notice that the 8/4 designation means two inches, not eight. Lumber thickness is quoted in quarters of an inch: 4/4 is one inch, 5/4 is one and a quarter, 8/4 is two.
Nominal versus measured dimensions
This is where most board-foot errors come from. Hardwood is normally sold by its rough, pre-surfaced size — a board sold as 4/4 measures a full inch before it is planed, and perhaps 13/16" after. The trade charges you for the rough dimension.
Softwood construction lumber works differently again: a "2×4" is actually 1½" × 3½" once surfaced, but is still called a 2×4. If you calculate board feet from the finished size of surfaced softwood you will under-count what you are being billed for.
Use the dimensions your supplier quotes. If you are calculating what you need for finished parts, add the planing allowance yourself before entering the numbers.
Common mistakes
Mixing length units is the big one: the formula wants length in feet while thickness and width are in inches. Entering a 72-inch board as "72 feet" inflates the result twelvefold. This calculator asks for the length unit explicitly for that reason.
Applying board feet to plywood is the other. Sheet goods are sold by the sheet or by area, so a board-foot figure for plywood is a number with no commercial meaning. Use the plywood sheet calculator instead.
Forgetting waste entirely is the quiet one. Rough lumber arrives with split ends, wane along the edges, and cup that has to be planed out. Ordering the exact calculated figure reliably leaves you short.
Know the volume. Now get the parts.
A board-foot figure tells you what to buy, not what to cut. Describe your project in a sentence and Plank CAD generates the part dimensions, joinery allowances and a full cut list — currently for bookcases and open storage cabinets.
Common questions
A 2×4 that is 8 feet long contains 5.33 board feet if you calculate from the nominal 2" × 4" dimensions. Calculated from the actual surfaced size of 1½" × 3½", it is 3.5 board feet. Suppliers almost always quote and charge by the nominal figure for construction lumber.
No. A linear foot is just length — it tells you nothing about thickness or width. Two boards can both be 8 linear feet long while containing very different volumes. Lumber is usually priced by the board foot for hardwood and by the linear foot for dimensional softwood and mouldings.
For clear, straight, kiln-dried stock cut into long parts, 10% is often enough. For rough-sawn lumber with wane and end splits, or for a project with many short parts where offcuts are hard to reuse, 20-30% is more realistic. Highly figured boards can run higher still because you are selecting around the figure.
Yards commonly round each board up to the next whole or half board foot, apply minimum charges on short or narrow pieces, and price by grade. Some also charge for the rough dimension on stock they have already surfaced. The formula here gives the true volume; the invoice reflects trade practice on top of it.