Board foot calculator: how to calculate board feet

A board foot is thickness in inches times width in inches times length in feet, divided by 12. So a 2x4 that is 8 feet long works out to 2 x 4 x 8 / 12 = 5.33 board feet. That is the whole formula, and it is the same math happening a hundred times a day at any lumber counter, where a contractor leans on the desk, asks what you can do on a couple of units of studs, and somebody converts the price per thousand into a per-piece number before the coffee gets cold.

Board foot calculator

Enter the thickness and width in inches, the length in feet or inches, how many pieces you have, and an optional price per board foot if you want a dollar figure along with the tally.

For softwood dimensional lumber, use the nominal size you would say out loud at the counter, so a 2x4 goes in as 2 by 4, not as the 1-1/2 by 3-1/2 it measures after milling.

The board foot formula

A board foot is a volume, 144 cubic inches of wood. Picture a board 1 inch thick, 12 inches wide, and 12 inches long: that slab is one board foot, and any other combination of dimensions that multiplies out to 144 cubic inches is one board foot too, as University of Minnesota Extension puts it in its guide to measuring timber.

Because lumber is usually quoted by length in feet, the working formula (the same one the American Hardwood Export Council publishes) divides by 12:

Board feet = thickness (in) x width (in) x length (ft) / 12

If you have the length in inches instead, divide by 144 and skip the unit conversion:

Board feet = thickness (in) x width (in) x length (in) / 144

Both versions give the same answer. Here is the math you can check by hand:

2x4, 8 feet long 1. Thickness x width: 2 x 4 = 8 2. Times length: 8 x 8 = 64 3. Divide by 12: 64 / 12 = 5.33 board feet

1x6, 10 feet long 1. 1 x 6 = 6 2. 6 x 10 = 60 3. 60 / 12 = 5 board feet

2x10, 16 feet long 1. 2 x 10 = 20 2. 20 x 16 = 320 3. 320 / 12 = 26.67 board feet

A 96-inch 2x4, using the inches version 1. 2 x 4 = 8 2. 8 x 96 = 768 3. 768 / 144 = 5.33 board feet, the same answer as the first example, because 96 inches is 8 feet

A stack: 50 pieces of 2x6x12 1. One piece: 2 x 6 x 12 / 12 = 12 board feet 2. The stack: 12 x 50 = 600 board feet

When the numbers get big, the trade switches to MBF, which means one thousand board feet (M stands for thousand, as the abbreviation tables in the PS 20 softwood standard spell out). Your 600-board-foot stack is 0.6 MBF, and lumber is bought and quoted by the MBF at the mill and distributor level, which is why "per thousand" is the phrase you hear across the counter.

Nominal vs actual size

Here is the part that trips people up, and it is not their fault. A 2x4 is sold as a 2x4, everybody calls it a 2x4, and it has never once measured 2 inches by 4 inches. After drying and planing (the milling step that takes rough lumber down to its finished dimensions), a 2x4 measures 1-1/2 by 3-1/2 inches. The 2x4 is the lumber industry's longest-running practical joke, and the punchline is that everybody is in on it.

For board footage, though, the joke has a rule behind it. The American Softwood Lumber Standard (PS 20), the U.S. Department of Commerce standard that governs softwood sizing, defines board measure using nominal thickness and nominal width: "Calculation of the number of board feet in a piece of lumber is based on the nominal dimensions of the cross section." So the 2x4 is counted as 2 x 4, full stop, even though you could measure the board in your hand and prove otherwise.

The difference is not small. If you used the actual dimensions, an 8-foot 2x4 would come out to 1.5 x 3.5 x 8 / 12 = 3.5 board feet instead of 5.33. That is about a third less wood on paper, and it is exactly how a well-meaning new hire under-prices every stud in the yard: they measure the board in their hand, do careful math, and still land on the wrong number.

For reference, here are the common nominal sizes and the actual dressed dry dimensions from the PS 20 tables:

Hardwood is measured differently

Everything above is the softwood world, where boards carry names. Hardwood plays by different rules, set out in the grading rules published by the National Hardwood Lumber Association (NHLA), and if you sell both, this is where the counter math splits.

Hardwood thickness is named in quarters of an inch. A 4/4 board ("four-quarter") is 1 inch thick, 5/4 is 1-1/4, 6/4 is 1-1/2, and 8/4 is a full 2 inches, on up to 16/4 at 4 inches. Hardwood is tallied on its rough, measured dimensions rather than a nominal name, and because hardwood boards come in random widths and lengths, each board gets measured on its own. Per the American Hardwood Export Council's measurement guide, widths above or below the half inch are rounded to the nearest whole inch, and lengths that fall between whole-foot increments are always rounded down to the whole foot. The quarter name follows the rough size, too: a 4/4 board finishes at about 13/16 inch after surfacing, but it is still sold as 4/4.

A worked example: an 8/4 walnut board, 7 inches wide and 9 feet long.

1. Thickness in inches: 8/4 = 2
2. 2 x 7 x 9 = 126
3. 126 / 12 = 10.5 board feet

The calculator above works for hardwood too. Enter the quarter thickness as inches (8/4 goes in as 2, 5/4 as 1.25) and use the measured width and length.

Board feet per linear foot: quick reference

If you price or quote by the linear foot, this table gives the board feet in each foot of length for the common softwood sizes.

To use it, multiply the figure for your size by the length in feet, so 60 linear feet of 2x6 at 1.0 board foot per linear foot is 60 board feet.

Pricing by the board foot vs by the piece

A yard buys softwood dimensional lumber by the thousand board feet from the mill or distributor, then sells it at the counter by the piece, where a 2x4x8 has a price tag on the rack, or sometimes by the linear foot for things like decking. Turning a per-MBF cost into a per-piece price is the board foot math from above plus your markup, and every counter person learns to do it in their head or on the back of a pick ticket.

Take a hypothetical cost of $800 per MBF (a round number for illustration, not a market quote). That is $0.80 a board foot. A 2x4x8 holds 5.33 board feet, so it costs about $4.27 before margin. A 2x6x12 holds 12 board feet, so it costs $9.60. Hardwood, and some specialty softwoods, skip the conversion entirely and sell by the board foot directly, so the counter tallies each board as it comes off the pile. Sheet goods sell by the sheet, and trim and moulding sell by the linear foot, each with its own math.

Here is the manual version, as it was put on one of our training calls with a building-supply store, the way generations of counter staff have learned it: "you have to multiply two by six by eight divided by 12, that gives you your board foot, then you have to multiply it by whatever it is per 1,000 to get it out to your per piece price." That is the job, repeated for every size on every load.

It matters because commodity lumber prices move week to week. A framing package quote is easier to build by the piece, but the yard needs to know the board footage to check cost, and the per-MBF number sitting behind a piece price needs updating whenever the market moves. Leave it alone for a month and the shelf tag quietly drifts off margin, which is a slow leak you only find at inventory time.

How a lumber yard POS should handle board feet

All of this argues for a POS that treats board feet as a first-class unit instead of a calculator taped to the register. The system should let you buy in one unit and sell in another, carrying board foot, MBF, linear foot, piece, and unit on the same item, and it should do the conversion on every line so the purchase order you send your vendor and the shelf price on the rack never disagree. When cost comes in per thousand and the customer walks out with six studs, somebody has to do that math, and it might as well be the computer.

That is what we built Rundoo to do, and you can see the full picture on our lumber yard POS page. Each product carries its own conversion factors (a 2x4x8 and a 2x4x10 each know their board footage), cost can be entered per MBF with the per-piece cost and margin calculated from it, and the inventory ledger carries quantities to four decimal places so nothing rounds away over a season of cuts. Vetter Lumber, a two-yard lumber business in Bluffton and Fort Jennings, Ohio, runs both yards on one Rundoo system, and their team worked through board-foot and MBF conversions for each stock size in training. As the Kinsingers put it, "Things are so much easier." If you are weighing systems more broadly, our guide to the best POS for lumber yards compares the options yards run today.