How to use the board foot calculator
Pick a kind of board, type its length and how many you have, and the board feet appear at once, with the math underneath and a picture of your lumber counted in slabs. Dimension lumber means the sizes sold as 2×4, 2×6 and so on, which are counted by their sold (nominal) size. Custom size is for any thickness and width you type, such as a rough-sawn board you measured. Hardwood counts the thickness in quarters of an inch, the way hardwood is often quoted. Add more boards to total a whole project. Type a price per board foot to get the cost, a percent for waste, and a density to get weight. The Convert tab changes board feet to cubic feet, cubic meters and liters. Nothing you type leaves your device.
What a board foot is
A board foot is a volume of wood: a slab 12 inches by 12 inches and 1 inch thick. That is 144 cubic inches, or one twelfth of a cubic foot, so there are exactly 12 board feet in a cubic foot. In metric it is 0.002359737216 cubic meters, which is 2.359737216 liters, so a cubic meter holds about 423.776 board feet. Lumber is priced by the board foot because a board's price follows its volume of wood, not just its length.
The formula
or: thickness (in) × width (in) × length (in) ÷ 144
Both forms give the same answer, because a foot is 12 inches. A 1×12 that is 12 feet long is 1 × 12 × 12 ÷ 12 = 12 board feet. A 2×6 that is 10 feet long is 2 × 6 × 10 ÷ 12 = 10 board feet. Multiply by the number of boards, then add them up. To get the cost, multiply the board feet by the price per board foot.
Nominal size and actual size
This is where most mistakes happen. Planed softwood lumber, like a 2×4, is measured for board feet by its nominal size, the name it is sold under, not by the smaller size you hold in your hand. A 2×4 that is 8 feet long counts as 2 × 4 × 8 ÷ 12 = 5.33 board feet by its sold size. The actual wood in it is smaller: at typical dry, planed sizes of 1½ by 3½ inches, it holds 3.5 board feet of wood. The calculator shows both numbers, the sold board feet and the actual wood, so you can see what you are paying for and what you really have. Standards change and boards vary, so the actual sizes on this page are typical values to check against the lumber you buy, and Custom size lets you use your own.
Hardwood and quarters
Hardwood is often sold by the board foot using the rough-sawn thickness of the board, and its thickness is commonly quoted in quarters of an inch: 4/4 means 1 inch, 5/4 means 1¼ inches, 6/4 means 1½ inches, and 8/4 means 2 inches. A board 8/4 thick, 7 inches wide and 8 feet long is 2 × 7 × 8 ÷ 12 = 9.33 board feet. Kiln-dried rough boards may run 1/16 inch thin (1/8 inch from 2 inches up) and still count as their quarter size. Boards planed on both sides are about 3/16 inch thinner than their quarter name up to 6/4, and about 1/4 inch thinner from 7/4 up, so a planed 4/4 board is about 13/16 inch. They are usually still sold by the quarter size, so ask how your yard counts.
Cost and waste
Enter your own price per board foot and the page multiplies it by the total. Prices change by species, grade, region and season, so the page shows no prices of its own. For waste, type the percent you want to allow for cuts, knots and mistakes, and the page adds it to the total. Zero is the default, because the right allowance depends on the job.
How many pieces do I need?
Divide the board feet you need by the board feet in one piece and round up. To get 40 board feet from 2×4s that are 8 feet long, each piece is 5.33 board feet, so you need 40 ÷ 5.33 = 7.5, which rounds up to 8 pieces. The calculator does this for the first board in your list.
Weight of lumber
Weight is volume times density. The page works out the cubic feet of wood in your pieces from their actual sizes and multiplies by a density in pounds per cubic foot. Pick a species and the page fills in the density of that wood dried to 12% moisture, or type your own. The species list comes from the USDA Forest Products Laboratory Wood Handbook, Chapter 5, Table 5-3b, which gives specific gravity (oven-dry weight over volume at 12% moisture). The page multiplies that by 62.4 pounds per cubic foot for water and by 1.12 to count the 12% water in the wood. Green or wetter lumber weighs more, and a single board can be several percent off its species average.
Mistakes that give the wrong number
- Using the actual size of a 2×4 (1½ × 3½) when the lumber is sold by its nominal size (2 × 4), or the reverse. Know which number you want.
- Mixing feet and inches. The formula with the length in feet divides by 12, and with the length in inches divides by 144.
- Forgetting the number of pieces. The formula gives one board; multiply for the whole stack.
- Counting hardwood by its planed thickness when it was sold by its rough quarters.
- Skipping the waste allowance and coming up short.
- Forgetting that metric sizes need converting: 25.4 millimeters make an inch.
Where the numbers come from
- A board foot is 144 cubic inches (a slab 12 in × 12 in × 1 in), one twelfth of a cubic foot. The cubic meter and liter values follow exactly from 1 inch = 25.4 millimeters (NIST SP 811).
- Planed softwood is counted by its nominal size (a general description of the board foot). Hardwood is counted by its thickness in quarters with the width and length measured: the hardwood grading rules (the NHLA rules, as summarized by the American Hardwood Export Council) give the standard thicknesses 4/4 = 1 inch up to 16/4 = 4 inches, the scant allowance for kiln-dried boards, and the 3/16 and 1/4 inch taken off in planing.
- Typical actual sizes of dimension lumber are the dry, dressed minimums in Table 3 of the American Softwood Lumber Standard (NIST PS 20-25): 1 inch boards dress to 3/4, 2 inch to 1 1/2, 4 inch to 3 1/2, and widths of 6, 8, 10 and 12 inches to 5 1/2, 7 1/4, 9 1/4 and 11 1/4.
- All the arithmetic is exact: lengths and sizes are kept as exact fractions and rounded only for display.
Questions
How many board feet are in a 2×4×8?
5.33 by the sold size: 2 × 4 × 8 ÷ 12. The actual wood in it, at typical dry sizes of 1½ by 3½ inches, is 3.5 board feet.
How do you calculate board feet?
Multiply the thickness in inches by the width in inches by the length in feet and divide by 12. Multiply by the number of boards.
How many board feet are in a cubic foot?
12. A board foot is 144 cubic inches and a cubic foot is 1,728.
How many board feet are in a cubic meter?
About 423.776, because a board foot is 0.002359737216 cubic meters.
Is a board foot nominal or actual?
For planed softwood like a 2×4, it is counted by the nominal (sold) size. For hardwood it is counted by the thickness in quarters (4/4 counts as 1 inch) and the measured width and length. This page shows the sold board feet and the actual wood side by side.
What does 4/4 mean on hardwood?
The thickness in quarters of an inch: 4/4 is 1 inch, 5/4 is 1¼ inches, 8/4 is 2 inches.
Can I use metric measurements?
Yes. Switch to Metric at the top and type millimeters for thickness and width and meters for length. The answer is still in board feet, with cubic meters beside it.
Can I share my boards?
Yes. Share saves only the boards (kind, size, length and count) for 90 days so the link can show the same total, and makes a picture for Facebook. It never saves the price, the waste or the density.