Board Foot Calculator

Background.

Eight boards of 6/4 hardwood, each 7.25 inches wide and 10 feet long, from a yard quoting 8.75 per board foot: how much lumber is that, and what will it cost? The answer comes in board feet, the unit hardwood and rough lumber are sold by. Unlike a linear foot, a board foot accounts for thickness, width, and length. That makes it a volume unit, not just a length unit. Those eight boards contain 72.5 board feet before waste and 81.2 board feet after a 12 percent allowance, which at that price comes to 710.50.

Lumber vocabulary is easy to misread. A 10-foot board and a 10-board-foot board are not the same thing. A board that is 1 inch thick, 12 inches wide, and 12 inches long is one board foot. A board that is 2 inches thick, 6 inches wide, and 12 inches long is also one board foot. Hardwood dealers often price rough lumber by board foot because boards vary in width and thickness. Dimensional construction lumber is often priced by piece, but board-foot volume remains useful for comparing material volume.

The National Hardwood Lumber Association states that board feet are the unit of measure of lumber and defines one board foot as 12 inches wide by 12 inches long by 1 inch thick, or 144 cubic inches. USDA Forest Products Laboratory publications discuss board-foot conversion and lumber volume because sawlog and lumber accounting can differ from pure cubic volume, and the Wood Handbook provides broader technical background on wood products.

The arithmetic is thickness in inches times width in inches times length in feet, divided by 12. The 12 appears because a board foot is 1 inch thick, 12 inches wide, and 1 foot long. Waste allowance is applied after multiplying by quantity, so the 12 percent in the example lifts 72.5 board feet to 81.2.

What that arithmetic gives you is physical volume from the dimensions you type. A lumberyard's invoice can differ. Rough hardwood is sold by nominal thickness in quarters of an inch (4/4, 5/4, 6/4, 8/4), surfaced boards come out thinner than their nominal rough thickness, some yards tally before surfacing, and random-width hardwood rules use surface measure and standard thickness with their own rounding. Enter the dimensions your supplier prices on, and treat the supplier's official tally as the figure that settles the bill.

What is board foot calculator?

A board foot is a unit of lumber volume equal to 144 cubic inches. The classic reference piece is 1 inch thick, 12 inches wide, and 12 inches long. A board-foot calculation uses thickness, width, length, and quantity to compute that volume. The primary output is board feet, with cubic-inch, cubic-foot, and cost equivalents.

The distinction that trips buyers up is between nominal and actual size. Rough lumber is often sold before final surfacing, while surfaced lumber has been planed and is thinner than its nominal size. Nominal thickness such as 4/4 means four quarters of an inch in rough-lumber language, and hardwood yards commonly keep billing a surfaced board at that nominal thickness even after planing has taken it to about 13/16 inch. Softwood construction lumber goes further: a 2×8 measures about 1½ by 7¼ inches, yet softwood is customarily tallied on its nominal 2 by 8. Tally is the word for the yard's own accounting method, and it decides which set of dimensions the price applies to.

The calculation is valid for user-entered dimensional volume. It is not a grading tool, a log-scaling tool, or a substitute for NHLA inspection rules. Commercial invoices may use standard thickness, surfaced-measure rules, dry tally, or other conventions. For exact billing, use the supplier's tally.

How to use this calculator.

1. 01Enter the board thickness in inches. For rough hardwood, convert quarter notation by dividing by four: 4/4 is 1, 5/4 is 1.25, 6/4 is 1.5 and 8/4 is 2. For planed stock, measure the real thickness.
2. 02Enter the width in inches and the length in feet. If your tape gives length in inches, divide by 12 first, so a 96-inch board is 8 feet.
3. 03Enter how many boards share those dimensions. For a stack of random-width boards of the same thickness and length, you can add the widths together and enter the sum with a quantity of 1; the board-foot total comes out the same.
4. 04Set a waste allowance for knots, checks, end splits, milling loss and grain or colour matching. Use 0 if you only want the net volume.
5. 05Enter the yard's price per board foot to get a cost estimate, or leave it at 0 to skip cost.
6. 06Compare the answer with the lumberyard's official tally before you pay.

The formula.

The board-foot formula is a volume conversion. Thickness and width are commonly measured in inches, while board length is commonly measured in feet. Multiplying thickness by width by length gives inch-inch-foot units. Dividing by 12 converts the 12-inch width component of a one-board-foot reference volume. The result is board feet. If length were in inches instead, the product would be cubic inches and the divisor would be 144; the length field here is in feet, so the divisor is always 12.

The worked example uses 1.5 inch thickness, 7.25 inch width, and 10 foot length. Multiplying those values gives 108.75. Dividing by 12 gives 9.0625 board feet per board. Eight boards therefore contain 72.5 board feet before waste. Waste is applied as a multiplier: 1 plus 12/100 equals 1.12. Multiplying 72.5 by 1.12 gives 81.2 board feet.

Because the formula is a plain product, each dimension scales the answer in proportion: double the thickness and the board feet double, add 10 percent to the width and they rise 10 percent. That is also why widths can be summed for boards of equal thickness and length.

The cubic equivalents are included for clarity. Because one board foot is 144 cubic inches, 81.2 board feet equals 11,692.8 cubic inches. One cubic foot is 12 × 12 × 12 = 1,728 cubic inches, which is exactly 12 board feet, so 81.2 board feet equals 6.7667 cubic feet. These conversions are useful when comparing board-foot volume with slabs, turning blanks, or shipping estimates, but they do not account for density or moisture weight.

Commercial lumber measurement can differ. NHLA rules use surface measure and standard thickness concepts for hardwood grading and tally. Lumber may be measured before surfacing. Fractions and random widths may be rounded according to trade rules. The formula is therefore best understood as physical volume from entered dimensions. If you enter actual surfaced dimensions, the result is actual physical volume. If you enter nominal rough dimensions, the result is nominal board-foot volume.

Cost is board feet times price per board foot, taken on the waste-adjusted figure. If the order target is 81.2 board feet and the price is 8.75, cost is 710.50. Some yards round order quantities or price by board rather than exact computed volume, so invoices should be checked against supplier practice.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Hardwood Lumber Association (2023). "NHLA Grading Rules." NHLA.
2. [2]Ross, R.J., ed. (2021). "Wood Handbook: Wood as an Engineering Material." USDA Forest Service, Forest Products Laboratory.
3. [3]Verrill, S., Herian, V., and Spelter, H. (2004). "Estimating the board foot to cubic foot ratio." USDA Forest Service, FPL-RP-616.
4. [4]U.S. Department of Agriculture (n.d.). "Hardwood Lumber Grades." USDA PDF.
5. [5]National Institute of Standards and Technology (2023). "NIST Handbook 133, Appendix E: General Tables of Units of Measurement." U.S. Department of Commerce.