Board Foot Calculator
1 board foot = 144 in³ = 1/12 ft³. Formula: BF = (L × W × T) / 144 (all dimensions in inches).
- Board foot definition: 1 BF = 144 in³ = 1/12 ft³.
- Formula: BF = (Length × Width × Thickness) / 144 when all dimensions are in inches.
- Mixed ft/in and m/cm inputs are converted to inches first, then used in the standard formula.
Lumber price comparisons become much easier when boards of different widths and lengths share one volume unit. This board foot calculator converts thickness, width, length, and quantity into board feet per piece and total board feet, then applies a price per board foot. It works with mixed metric or imperial input units, making it useful for hardwood purchasing, millwork estimates, slabs, rough lumber, and shop planning.
How to use the board foot calculator
Enter the number of matching pieces, the thickness, width, and length of each piece, and choose the unit beside every dimension. Add the supplier’s price per board foot to estimate cost. The results show the board feet in one piece, total board feet for the quantity, and the calculated lumber subtotal.
Run boards with different dimensions as separate groups and add their totals. Measure the dimensions used by the seller—often the rough or stated dimensions for hardwood—not automatically the final planed size you expect after milling. Confirm the yard’s tally and rounding rules before purchasing because commercial practices can vary.
Board foot formula
When all dimensions are in inches, the standard calculation is:
Board feet = Thickness (in) × Width (in) × Length (in) ÷ 144
For multiple identical boards, multiply by quantity. Because one foot equals 12 inches, a piece measuring 1 in thick × 12 in wide × 12 in long contains 144 cubic inches, or one board foot. A board foot is therefore a unit of volume. It should not be confused with a linear foot, which measures only length, or a square foot, which measures area.
The legal metrology definition is documented in NIST Handbook 130 material on lumber measurement. The calculator standardizes entered dimensions internally, so centimeters, millimeters, feet, meters, and inches can be combined without manual conversion.
Worked board foot example
Suppose you need eight rough boards, each 1.25 in thick, 8 in wide, and 10 ft long. Convert 10 ft to 120 in. One board contains 1.25 × 8 × 120 ÷ 144, or about 8.33 board feet. Eight pieces total about 66.67 board feet.
At $7.50 per board foot, the calculated lumber value is approximately $500.00 before tax, delivery, waste, grading premiums, or the supplier’s tally conventions. This example keeps full precision until the final monetary result; rounding each board too early can accumulate an avoidable error across a large order.
Rough size versus finished size
A rough board may lose thickness and width during jointing, planing, straightening, and edge trimming. If you calculate only from the desired finished part, you may understate the volume that must be purchased. Use the dimensions and measurement method on which the seller prices the stock, then create a separate cut list for finished parts.
Nominal softwood dimensions present a related issue: a named 1×6 does not usually measure a full one inch by six inches after surfacing. Board-foot purchasing is more common for hardwoods and rough lumber, while construction lumber is often sold per piece or linear foot. Confirm which dimensions the quote uses rather than assuming the nominal name is the billable size.
Irregular boards and slabs
Live-edge slabs and tapered boards do not have one constant width. Many sellers use an agreed average width, sometimes measured at specified intervals, to produce a tally. A simple method is to average several representative widths along the board, but you should follow the supplier’s written rule because edge defects, bark, wane, and measurement points may be treated differently.
The calculator assumes a rectangular solid with constant thickness, width, and length. For a slab with major thickness variation or voids, divide it into reasonable sections or use the yard’s measured tally. The National Hardwood Lumber Association rules resources are useful when grade and measurement practice affect a transaction.
Planning waste and yield
Board feet describe purchased volume, not guaranteed finished-part yield. Defects, sapwood restrictions, grain matching, color selection, checks, twist, cup, machining, and cut orientation can reduce usable yield. Build a cut list, nest parts against real board sizes, and add an explicit project allowance informed by quality requirements.
Wide clear parts or continuous grain sequences may require more selective stock than a simple volume total suggests. Conversely, a project with many small components may use offcuts efficiently. Keep the calculated net requirement, planned allowance, and final purchase tally as separate figures so future estimates can be improved from actual yield.
Cost calculation and price comparisons
The cost relationship is straightforward: Total cost = Total board feet × Price per board foot. However, species, grade, thickness, drying method, surfacing, figure, width, certification, and minimum quantities can change the unit price. Confirm whether a quote includes milling, straight-line ripping, tax, or freight.
To compare a per-piece offer with a board-foot price, calculate the board feet in that piece and divide its price by the result. For construction framing by piece count, the framing calculator is a better starting point. For sheet goods, use area and sheet yield rather than treating plywood as ordinary rough hardwood inventory.
Unit and measurement checks
Measure thickness and width in the same condition used for pricing. Convert feet to inches when checking the formula manually, and do not divide by 144 twice. For metric stock, the calculator avoids a common mistake by converting the dimensions to a consistent volume before expressing the result in board feet.
If you also need a geometric cubic volume, the volume calculator can provide a separate check. One board foot equals 144 cubic inches, but that relationship does not determine how many finished parts a board will yield.
Common mistakes to avoid
- Confusing board feet with square feet or linear feet.
- Using finished dimensions when the supplier bills rough dimensions.
- Forgetting to convert length in feet to inches in a manual calculation.
- Rounding every piece before multiplying a large quantity.
- Assuming nominal construction-lumber dimensions are actual dimensions.
- Treating calculated lumber volume as guaranteed defect-free yield.
Frequently asked questions
What is one board foot?
One board foot is 144 cubic inches of lumber, equivalent to a volume 1 inch thick, 12 inches wide, and 12 inches long.
How do I calculate board feet?
Multiply thickness in inches by width in inches by length in inches, then divide by 144. Multiply by quantity for matching pieces.
Is a board foot the same as a square foot?
No. A square foot measures area. A board foot measures volume and includes thickness as well as width and length.
Should I use nominal or actual dimensions?
Use the dimensions and tally method on which the seller bases the price. For rough hardwood, that may differ from the final planed size.
How do I calculate the cost per board?
Calculate board feet in one board and multiply by the price per board foot. Add separate charges such as milling, delivery, and tax afterward.
Does the calculator include waste?
No. It reports geometric board-foot volume. Add a project-specific allowance based on defects, milling loss, part layout, and appearance requirements.