Board Feet Calculator

A board foot is a volume, not a length: 144 cubic inches of wood, which is a piece a foot square and an inch thick. It exists because lumber comes in awkward combinations of dimensions, and a yard needs one number that lets a 1×12 and a 2×6 be priced against each other fairly. Both of those are one board foot per running foot.

The formula everybody quotes is thickness × width × length ÷ 12, with thickness and width in inches and length in feet. That is the same calculation as thickness × width × length ÷ 144 with everything in inches, which is what the calculator above uses. Working entirely in inches means the feet and inches inputs cannot drift apart, and it makes the working visible when the answer looks wrong.

The mistake that costs money: nominal versus actual

A board sold as a 1×6 does not measure one inch by six. After it has been dried and run through a planer it measures about three quarters by five and a half. The name refers to the rough size before surfacing, and the yard bills on that nominal size.

This matters because the arithmetic runs on whichever number you feed it. Enter the actual 0.75 inch thickness when the yard is charging for a full inch and you will under-buy by 25 percent. Enter 5.5 instead of 6 for the width and you lose another 8 percent. On a job needing 200 board feet, that combination leaves you about 60 board feet short and confused about why the invoice does not match.

The rule is simple once stated: use the nominal size the yard is billing on. If you are calculating how much timber you physically have, rather than what it costs, use the actual measured size instead. Those are two different questions and they give two different answers, both correct.

Quarter sizing, and why hardwood is sold in fractions

Hardwood thickness is quoted in quarters of an inch. A board marked 4/4, spoken as "four quarter", is one inch nominal. 5/4 is an inch and a quarter, 8/4 is two inches, 12/4 is three. The convention survives because hardwood is sold rough-sawn and thicknessed by the buyer, so the useful number is what the board started at rather than what it currently measures.

A 4/4 board that has been surfaced on two faces will measure about 13/16 of an inch. It is still sold as 4/4 and still billed as a full inch. The selector in the calculator writes the nominal decimal for you, because somebody standing at a lumber rack is reading "8/4" off a sticker rather than dividing in their head.

Waste, and how much to allow

Nobody uses every inch of every board. Defects get cut out, ends get trimmed, the grain runs the wrong way on one piece, and something gets ruined at the router table. The allowance depends on the work rather than on the person:

• 10 percent for straightforward crosscutting from clear stock.
• 15 percent for general furniture work, which is the default here.
• 25 to 30 percent when cutting around knots, matching grain across a panel, or working with figured stock where the good sections are short.
• 40 percent or more for curved parts cut from straight boards, where the offcut between two curves is unusable.

Buying the whole job at once matters more than the exact percentage. Boards from one lift were milled from similar logs and dried together, so they match in colour and moisture. A replacement board bought three weeks later can be visibly different in a glued-up panel, and no amount of finishing hides it.

Board feet, linear feet and square feet

These three get confused constantly, and the confusion is expensive because a yard will happily sell you what you asked for.

Linear feet measures length only, ignoring thickness and width. Trim, moulding and dimensional framing lumber are usually sold this way: a 10 foot 2×4 is 10 linear feet regardless of what it weighs.

Square feet measures area, ignoring thickness. Sheet goods, flooring and decking are sold this way, because for those products the thickness is fixed by the product name.

Board feet measures volume. Hardwood and rough lumber are sold this way, because thickness is a variable the buyer chooses and it has to be paid for.

A quick sanity check: any board that is one inch nominal thick and twelve inches wide gives exactly one board foot per linear foot, which makes it an easy mental benchmark to work from.

Working in metric

Outside North America timber is usually sold by the cubic metre. One board foot is 0.0023597 cubic metres, so a cubic metre is about 424 board feet. The calculator gives cubic feet and cubic metres alongside the board feet, which is the figure to quote when comparing an American price against a European or Australian one.

What the price per board foot includes

Hardwood pricing normally assumes rough stock, surfaced on none or two faces. Surfacing on four sides, straight-line ripping, or selecting for width all attract a premium, and wide boards cost disproportionately more because the log they came from was larger. A quoted price of six dollars a board foot for 4/4 walnut is not the price of a finished, flat, ready-to-use board of any particular width.

Grade also moves the price substantially. FAS, the top grade under the National Hardwood Lumber Association rules, requires long clear cuttings and costs accordingly. Number 1 Common yields shorter clear pieces at a much lower price, and for furniture built from parts under about three feet it is often the more economical choice even after the extra waste.