What is a board foot?
A board foot is a volume of wood: a board 1 in thick, 12 in wide and 1 ft long, which is 144 cubic inches. 12 of them make a cubic foot. A price by the board foot is one price for boards of any width and any length.
The formula is thickness in inches × width in inches × length in feet ÷ 12.
Worked example. One board of 4/4 stock, 6 in wide and 8 ft long, then a second of 8/4, 8 in wide and 10 ft long.
- First board: 1 in × 6 in × 8 ft ÷ 12 = 4.00 board feet
- Second board: 2 in × 8 in × 10 ft ÷ 12 = 13.33 board feet
- Both: 17.33 board feet
- At $9.50 a board foot: $164.67
Add a line for each size of board, with how many of it you need. "Copy" gives the list as the rows of a spreadsheet, with the board feet of each line.
Nominal vs actual, rough vs surfaced
A hardwood yard writes thickness in quarters of an inch. Woodworkers Source lists 4/4 as about 1 in, 5/4 as about 1 1/4 in, 6/4 as about 1 1/2 in and 8/4 as about 2 in, and says the fraction names the thickness as the board was sawn, rough: a board that has been surfaced is thinner than its name. Type 4/4 or 8/4 in the thickness field as it is written on the rack.
The calculator works with the sizes you type, so type the sizes your yard prices by: ask whether that is the name of the board or what is left of it after planing. Its tally is the one you pay.
Softwood framing lumber is named by its nominal size too. A 2×4 of 8 ft counted at 2 in by 4 in comes to 5.33 board feet, although the surfaced board is smaller than its name. Enter the actual size instead if you want the wood that is really there.
Price per board foot vs per linear foot
A price by the board foot is the same for every size of board. A price by the linear foot belongs to one size: it is the price of one foot of that board, whatever its width and thickness.
To go from one to the other, multiply by the board feet in a foot of the board. A 4/4 board 6 in wide holds 0.5 board feet in each foot of length, so $9.50 a board foot is $4.75 a linear foot. Enter your price either way in the options. The calculator shows the cost and, for the first board of the list, the same price said the other way.
Waste when milling rough lumber
Rough boards lose wood on the way to a part: the faces are planed flat, the edges are jointed, the ends are trimmed, and a knot or a split is cut around. How much depends on the boards and on the parts, so the calculator starts with no extra and leaves the percentage to you.
With 20% on 10.00 board feet, the figure to buy is 12.00 board feet, and the cost is worked out on that figure: $114.00 at $9.50 a board foot. The first figure stays on the page as what your parts hold.
In metric, enter the thickness and the width in millimetres and the length in metres. One board foot is 0.00236 m³, by the conversion factors of NIST. A board of 25 × 150 mm and 2.4 m is 0.009 m³, or 3.81 board feet.
Questions about board feet
How many board feet in a 2×4×8?
5.33 board feet, counted at its nominal 2 in by 4 in: 2 × 4 × 8 ÷ 12.
How many board feet in a cubic foot?
12. A cubic foot is 1,728 cubic inches and a board foot is 144.
How do I price a hardwood order?
List each board with its thickness, width and length, add the percentage you expect to lose in milling, and enter the yard’s price per board foot. The example list of 17.33 board feet costs $164.67 at $9.50.
How do I convert a price per board foot to a price per linear foot?
Multiply it by thickness × width ÷ 12, both in inches. For a 4/4 board 6 in wide, $9.50 a board foot is $4.75 a linear foot.
Sources
- Woodworkers Source, What Does 4/4 Mean? (Or 6/4, 8/4, 5/4?). 4/4 means approximately 1 in thick, 5/4 approximately 1 1/4 in, 6/4 approximately 1 1/2 in, 8/4 approximately 2 in and 12/4 approximately 3 in. The fractions identify the rough milled thickness of lumber; the actual size depends on whether it is still rough sawn or has been surfaced. Read on .
- Archtoolbox, Lumber Dimensions: Nominal vs Actual. Surfaced softwood lumber: a 2 x 10 is 1 1/2 x 9 1/4 in and a 2 x 12 is 1 1/2 x 11 1/4 in; a 4 x 4 is 3 1/2 x 3 1/2 in and a 6 x 6 is 5 1/2 x 5 1/2 in; a 1 x 4 is 3/4 x 3 1/2 in and a 1 x 6 is 3/4 x 5 1/2 in. Standard lengths run from 6 to 24 ft in steps of 2 ft. Read on .
- National Institute of Standards and Technology, Guide to the SI (Special Publication 811), Appendix B.9: conversion factors. A foot is 0.3048 m and an inch 2.54 cm, exactly. A cubic foot is 0.02831685 m³, a cubic yard 0.7645549 m³, a US gallon 3.785412 L, a square foot 0.09290304 m² and an acre 4,046.873 m². Read on .
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