Free calculator
Board foot calculator
Work out how much lumber you are buying. Enter the thickness, width and length of a board and how many you need, in inches and feet or in millimetres, and read the board feet, the cubic metres and the cost.
The formula
Thickness × width × length ÷ 144.
A board foot is 144 cubic inches: a piece 1 inch thick, 12 inches wide and 12 inches long. Multiply the three sizes in inches and divide by 144, or with the length in feet, divide by 12.
Worked example
Four boards of 8/4 white oak, 6 inches wide and 8 feet long. 8/4 is 2 inches and 8 feet is 96 inches, so each board is 2 × 6 × 96 ÷ 144 = 8 board feet, and the four come to 32 board feet. At $11.00 a board foot, the rough Canadian retail price Mortise uses for white oak, that is $352.00.
By hand, step by step
- Measure the thickness in inches. Use the nominal or rough size the yard sells by: 4/4 is 1 inch, 8/4 is 2 inches, a 2x4 is 2 by 4.
- Measure the width in inches.
- Measure the length in inches. A length in feet works too: divide by 12 instead of 144 in the next step.
- Multiply thickness by width by length and divide by 144. That is the board feet in one board.
- Multiply by the number of boards for the total, and by the price per board foot for the cost.
Questions
Board feet, answered.
- How do you calculate board feet?
- Multiply thickness by width by length in inches and divide by 144. A board foot is 144 cubic inches, a piece 1 inch thick, 12 inches wide and 12 inches long. With the length in feet, divide by 12 instead.
- Do I use the nominal or the actual thickness?
- Use the nominal size, the way a lumberyard charges. A 2x4 counts as 2 by 4 inches though it measures 1½ by 3½, and 4/4 hardwood counts as a full inch even after it is planed thinner. Mortise counts board feet the same way in its cut list.
- What do 4/4 and 8/4 mean?
- They are rough thickness in quarters of an inch: 4/4 is 1 inch, 5/4 is 1¼ and 8/4 is 2 inches, so an 8/4 board has twice the board feet of a 4/4 board the same size. Surfaced on both faces, Mortise draws 8/4 at 1¾ inches. Type 8/4 into the calculator and it reads as 2 inches.
- How much does a board foot of lumber cost?
- It depends on the species and the yard: multiply the board feet by the price per board foot. The rough Canadian retail prices Mortise uses for estimates run from $1.25 for SPF to $18 for walnut, with white oak at $11. Buy a little more than the total, since ends are trimmed square and some wood is lost to defects.
- How do I work out cubic metres for metric timber?
- Multiply thickness by width by length in millimetres and divide by 1,000,000,000. Metric yards sell by the cubic metre of the actual section, and one cubic metre is about 424 board feet. Switch the calculator to millimetres to see both.
Mortise
Board feet for a whole project.
Mortise is a woodworking app that runs in the browser at woodworking.app. Design the whole project from real boards at their real sizes and get the board feet for every part, with a shopping list of the boards to buy.