Board Foot Calculator

How to use it

1. Board list: enter each board's species, thickness, width, length and how many, with a price if you have one. Thickness is a quarter size (4/4 is 1 in.) or any thickness you type under Other. Lengths are in feet: 8, 8.5 and 8' 6" all work.
2. Choose how the yard prices it: per board foot, per linear foot or per cubic metre. Each row also shows the price the other way, so you can compare yards.
3. From finished parts: enter each part's finished thickness, width and length, the species and grade, and check the allowances. The calculator picks the rough thickness for each part and gives the board feet to order at each thickness.
4. Print it or copy the link to take to the yard. The lists are also saved in this browser.

The board foot formula

A board foot is 144 cubic inches: a piece 12 in. wide, 12 in. long and 1 in. thick, or any shape with the same volume. With every size in inches, board feet = thickness × width × length ÷ 144. With the length in feet it is thickness × width × length ÷ 12.

• An 8/4 walnut board 7 1/4 in. wide and 8 ft 6 in. long: 2 × 7.25 × 102 ÷ 144 = 10.27 board feet.
• A 4/4 poplar board 6 in. wide and 10 ft long: 1 × 6 × 10 ÷ 12 = 5 board feet.
• An 8 ft 2x4: 2 × 4 × 8 ÷ 12 = 5.33 board feet, on the nominal size.
• A metric board 27 mm thick, 180 mm wide and 2.8 m long: 0.027 × 0.18 × 2.8 = 0.013608 m³, and 0.013608 ÷ 0.002359737216 = 5.77 board feet.

One board foot is exactly 0.002359737216 m³, since an inch is exactly 25.4 mm, and one cubic metre is 423.78 board feet. Switch the calculator to mm to work in cubic metres with the board-foot equivalent beside them; many European yards sell hardwood by the cubic metre.

Nominal and actual thickness

Hardwood is sawn and sold in quarters of an inch, and board feet are figured on that nominal rough thickness. Under the NHLA rules for hardwood lumber, board footage of surfaced lumber is measured before surfacing, so 4/4 planed to 13/16 in. still counts as 1 in., and lumber thinner than 1 in. is counted as 1 in. Rough kiln-dried lumber may also arrive a little thin: up to 1/16 in. under nominal from 3/8 to 1 3/4 in. and 1/8 in. under at 2 in. and thicker, as AHEC's summary of the rules puts it. It is still counted at nominal.

Softwood is the same idea with different names. The American Softwood Lumber Standard (PS 20-25) figures board feet from the nominal thickness and width, so a 2x4 counts as 2 × 4 even though a dry one is dressed to 1 1/2 × 3 1/2 in. In the board list, enter a 2x4 as 8/4 and a width of 4.

The rules take 3/16 in. off rough lumber up to 1 1/2 in. thick and 1/4 in. off 1 3/4 to 4 in. Surfacing one side only is left to the contract between buyer and seller, and boards surfaced at a yard are often a little thicker than this table, so measure them.

Buying rough lumber and choosing quarters

Rough boards are rarely flat. They cup across the width, bow along the length and sometimes twist, and jointing and planing them flat costs thickness. The calculator plans on 1/4 in. off the nominal thickness, which is what we budget for boards of ordinary length that have been dried properly; that is the NHLA surfacing allowance from 7/4 up, and 1/16 in. more than it below that.

• Long, wide or cupped boards need more. A slight bow in a 10 ft board becomes a lot of wood to take off if you flatten it whole. Cut parts to rough length and rip wide boards before jointing, so you flatten short, narrow pieces. If a part has to be long and full thickness, buy the next quarter up.
• Let it settle. Wood moves when it is cut open. Rough-cut the parts a little oversize, let them sit for a day or two, then mill them to final size.
• Thin parts: planing 4/4 down to 1/2 in. for drawer sides throws half the board away. Resawing thicker stock on a band saw can give two thin parts from one board, and some yards sell thinner stock.
• Thick parts: 1 1/2 in. legs come from 8/4 and 2 3/4 in. legs from 12/4. Gluing two boards face to face is the other way: two pieces of 6/4 milled to 1 1/4 in. make a 2 1/2 in. blank, if a glue line on the leg is acceptable.

Grades and yield

Hardwood is graded by how much of each board is clear, defect-free wood in usable pieces. The NHLA rules set, for each grade, the smallest board admitted, the smallest clear piece ("cutting") that counts and the least share of the board those cuttings must cover. A board is graded from its poorer face, except where the grade says otherwise.

The planner sizes a rough blank for every part: the part plus 1 in. in length and 1/4 in. in width by default, from the thinnest quarter that mills to it, counted at the nominal thickness. It adds up the blanks at each thickness, divides by the grade's minimum yield, and adds an offcut allowance (15% by default) for the ends and edges left when your parts don't exactly fill the clear areas. Every allowance can be changed, and the methodology page lists the rules and sources behind these figures.

The example is a small walnut side table with a glued-up top, 8/4 legs and 4/4 aprons and shelf. Its finished parts hold 5.78 board feet of wood. The rough blanks come to 5.91 board feet of 4/4 and 2.75 of 8/4; divided by 83 1/3% for FAS and with 15% more for offcuts, that is 8.16 and 3.79, so the order is 9 board feet of 4/4 and 4 of 8/4.

Treat the result as a planning estimate. The grade sets the least clear wood a board can have, and good boards beat it, but how much you use depends on the boards in the pile, how your part sizes fit between their defects and whether you need color and grain to match. A board or two extra of anything that has to match is cheaper than hunting later for more from the same log.

Random widths and lengths at the yard

Hardwood comes in random widths and lengths. NHLA standard lengths run in whole feet from 4 to 16 ft; FAS boards are at least 6 in. wide and 8 ft long, and No. 1 Common boards at least 3 in. wide and 4 ft long. A yard that tallies with a board rule measures each board's surface measure (width in inches × length in feet ÷ 12), drops any fraction of a foot in length, rounds the surface measure to the nearest whole foot (exact halves go alternately up and down) and multiplies by the thickness.

That is why the yard's figure can differ from yours. The 8/4 walnut board above, 7 1/4 in. × 8 ft 6 in., is 10.27 board feet measured exactly, but tallied at 8 ft it is 5 surface feet and 10 board feet; a 4/4 board 6 1/2 in. × 10 ft is 5.42 exactly and 5 tallied. Tick "Round each board like a yard tally" in the board list to see the yard's way. Bring a tape, write down each board you pull from the pile, and check the total against the invoice.

Kiln-dried hardwood measured after drying is sold on its net board feet: the model state regulation printed in the NHLA rules, adopted by the National Conference on Weights and Measures, allows no footage to be added for shrinkage in the kiln.

Price per board foot or per linear foot

Rough hardwood is priced per board foot, but surfaced boards, moldings and softwood are often priced per linear foot or per piece. To compare, convert with the board feet in one linear foot, thickness × width ÷ 12 on the nominal size:

• Price per linear foot = price per board foot × thickness × width ÷ 12.
• Price per board foot = price per linear foot × 12 ÷ (thickness × width).

A board sold surfaced four sides as a "1x6" is 3/4 × 5 1/2 in., but its board feet still come from 1 × 6, half a board foot per foot of length. At a price per linear foot, a narrow board can cost far more per board foot than rough stock you mill yourself.

Board feet and cubic metres

In metric mode the calculator works in millimetres and cubic metres, with the board-foot equivalent beside every total and a price per cubic metre or per metre of board. The quarter sizes stay available, at their exact metric equivalents (4/4 is 25.4 mm), for American hardwood bought in Europe; pick Other for a sawmill's own metric thickness.

Be careful converting softwood. PS 20-25 figures board feet on nominal sizes but cubic metres on the dressed size, so the two don't convert one to one: a dry 2x4 dressed to 1 1/2 × 3 1/2 in. has 66% of the volume its nominal 2 × 4 suggests.