What a board foot measures
Board footage describes lumber volume. A piece 1 × 12 × 1 foot contains one board foot because 1 × 12 × 12 = 144 cubic inches. A board foot is not a foot of length or a square foot of surface area.
Measure thickness, width and length consistently
For the common U.S. formula, record thickness and width in inches and length in feet. A length of 8 feet 6 inches is 8.5 feet. If every dimension is entered in inches, divide the cubic-inch product by 144 instead.
If you enter a length in inches into the formula that expects feet, convert it first: 8 inches is 8 ÷ 12 feet. Treating 8 inches as 8 feet makes the result twelve times too large. If you work in millimetres, convert all physical dimensions together; the board-foot definition stays the same.
Apply the board-foot formula
T(in) × W(in) × L(ft) ÷ 12
Or, if thickness, width and length are all in inches:
T(in) × W(in) × L(in) ÷ 144
For entered dimensions of 1 × 6 × 8 feet, one board contains 1 × 6 × 8 ÷ 12 = 4 BF.
Multiply by the number of boards
For identical pieces, multiply board feet per piece by the quantity. Ten boards at 4 BF each total 40 BF. Keep the per-piece figure unrounded when calculating cost or a list total.
Add a multi-size lumber list
Calculate each size separately, multiply by its own quantity, then add the line totals:
- 4 boards × 1 × 6 × 8 ft: 4 BF each × 4 = 16 BF.
- 2 boards × 2 × 8 × 6 ft: 8 BF each × 2 = 16 BF.
The combined list is 32 BF. Separate rows make it easier to retain each size, quantity and price basis.
Understand 4/4 and other rough thickness labels
Hardwood rough-thickness notation uses quarters of an inch as a rough basis: 4/4 is 1 inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. Surfacing removes material, so the finished size can be smaller and may depend on the board and processing.
4/4 thickness notation does not mean quarter-sawn lumber. One term describes a rough thickness basis; quarter-sawn describes a way the board is cut in relation to the log's growth rings.
Nominal vs actual measurements
A nominal label, rough dimension, surfaced size and measured size may describe different bases. The calculator does not silently convert one into another. When checking a supplier tally, use the basis the supplier applies. When calculating the geometric volume of a physical board, use its measured dimensions.
Price lumber by board foot
For a price you enter, cost = board feet × price per board foot. A known total can also be divided by the lumber's board footage to find an implied price per board foot. A currency option only changes formatting; it does not convert currencies.
Add an allowance only when useful
An allowance adds board-foot volume for a project-specific planning reason. It does not determine the size or number of additional boards, and no single percentage fits every material and project. Choose the value based on your own cuts, defects, matching needs and supplier guidance.
Metric measurements
Metric mode can take thickness, width and length in millimetres. The physical dimensions 25.4 × 152.4 × 2,438.4 mm equal 1 × 6 × 8 ft and therefore 4 BF. For volume comparisons, 40 BF is 3.333… cubic feet; one board foot is 0.002359737216 cubic metres by geometric conversion.
Board feet are not log-scale board feet
This formula uses dimensions of sawn lumber. Log rules such as Scribner, Doyle and International 1/4-inch estimate potential lumber yield from a log and use separate measurements and assumptions. Do not use a sawn-board calculator to scale logs.
Calculate your lumber list
Enter each size and quantity in the Board Foot Calculator to total board feet, cubic-volume equivalents and optional user-entered cost. Board footage does not determine a deck or fence layout. For deck-board counts and spacing, use the Deck Material Calculator; for fence runs, gates and material planning, use the Fence Calculator.
Sources: USDA Forest Service, Unit of Measure Conversion Factors for Roundwood Receiving Facilities and the American Hardwood Export Council's sawn-lumber measurement guide, and the USDA Forest Products Laboratory Wood Handbook section on growth rings and sawing. These explain the board-foot volume basis, log-rule distinction, rough-thickness notation and quarter-sawn grain orientation.
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