Board Foot Calculator

How It Works

The calculator multiplies thickness by width by length for one board, divides by 12, then multiplies by the number of boards. Thickness and width are in inches, and length is in feet.

NIST Handbook 130, for hardwood lumber, defines a board foot as the volume of a board 1 foot long, 1 foot wide, and 1 inch thick, which is 144 cubic inches. If you measure the length in inches too, divide by 144 instead of 12.

The last line of the Material List appears for the six sizes on the buttons. It reworks your total with the minimum dressed dry size of that board, so you can see how far the label is from the wood. For the formula step by step, read How to Calculate Board Feet.

See Methods and Sources

Worked Example

Here is the math for 12 boards, each a 1 by 8 that is 10 feet long, with 10 percent extra at a sample price of $4 per board foot.

1. 1 in x 8 in x 10 ft = 80
2. 80 / 12 = 6 2/3 board feet per board, or 6.67 rounded
3. 6 2/3 x 12 boards = 80 board feet
4. 80 board feet x 1.10 = 88 board feet with extra
5. 88 board feet x $4 = $352

The same 12 boards at an actual size of 3/4 by 7 1/4 inches come to 54.38 board feet, with nothing added for extra.

Board Feet by Board Size and Length

This table shows one board at each length, by nominal size. For a 12 foot 2 by 8, the answer is 16 board feet, so 10 of them make 160 board feet.

Nominal Size and Actual Size

The name on a board is not its real size. NIST calls a two by four a nominal size, used to describe approximate rather than actual dimensions, and the board is really 1 1/2 by 3 1/2 inches. The Southern Pine Inspection Bureau explains that boards get smaller as they are dried and surfaced.

The actual sizes below are the minimum dressed dry softwood sizes in the USDA Wood Handbook. Those boards are thinner and narrower than their names, so they hold fewer board feet.

The Wood Handbook warns that board measure depends on the thickness and width names used, so check which one your supplier means before you compare prices.

Hardwood Thickness in Quarters

Rough hardwood is usually named in quarters of an inch, so 4/4 is about 1 inch and 6/4 is about 1 1/2 inches. The rough and surfaced figures below come from the USDA Wood Handbook, where surfaced means planed on two sides. Surfaced sizes can differ by supplier, so measure your own stock.

The last column uses the rough thickness. McIlvain, a lumber supplier, says board feet are always calculated with the nominal rough thickness, so a 4/4 board counts as 1 inch even after it is surfaced to about 13/16 inch. Enter 1 in the Thick box for 4/4, 1.25 for 5/4, and 1.5 for 6/4.

Why a Supplier’s Tally Can Differ

A yard total may not match this calculator exactly, because of how each board is measured and rounded. McIlvain says a hardwood delivery’s tally drops fractions of length, so a 10 foot 7 inch board tallies as 10 feet, and rounds each board to a whole board foot. Rounding details vary by source, so ask your supplier which method it uses.

NIST Handbook 130 includes a uniform regulation for individual jurisdictions to adopt. Its section on retail hardwood sales, which excludes flooring and molding, rounds fractional lengths down to the next standard length. It works out surface measure from the full width, fractions included, and rounds to the nearest whole square foot, with half a square foot rounding down. It also says random width lumber measured after kiln drying is sold on net board footage, with nothing added for kiln shrinkage or surfacing. Softwood is often priced differently. McIlvain notes that softwood may be sold by the linear foot, so turn any price into the same unit before you compare.

How Much Extra to Add

The total above is net wood, and cutting out defects and trimming to size use up more. McIlvain gives these hardwood waste factors and does not say where the figures come from, so treat them as starting points.

Frequently Asked Questions

These cover the questions that come up most often.