Board foot calculator
Enter the thickness, width and length of a board to see its board feet. Add the number of pieces and a price per board foot to see the total and the cost.
This answer is for the example values in the boxes above. 5 pieces of 1 in by 6 in by 8 ft. Change the boxes to see your own answer.
A board foot is 144 cubic inches: the thickness in inches times the width in inches times the length in feet, over 12.
How it works
A board foot is a volume of 144 cubic inches: a board 12 inches long, 12 inches wide and 1 inch thick, or any piece with the same volume. With the thickness and the width in inches and the length in feet, the board feet are thickness times width times length, divided by 12. The calculator also gives the cubic feet, which are the board feet divided by 12.
The pieces multiply the total. A price per board foot gives the cost of the board feet shown.
Hardwood thickness in quarters
Hardwood thicknesses are named 4/4, 5/4, 6/4, 8/4 and so on. Choose quarters next to the thickness and type the top number, 8 for a board named 8/4. The calculator divides it by 4 and counts 2 inches.
Nominal and actual size
Softwood lumber is named by a nominal size that is larger than the piece. A 2 by 4 is 1 1/2 by 3 1/2 inches, and a 1 by 6 is 3/4 inch thick and 5 1/2 inches wide. For softwood lumber 1 inch or more thick, a federal rule counts the board feet from the nominal thickness and width and the actual length, and counts a nominal thickness under 1 inch as 1 inch. The calculator counts the size you type, so type the size your seller counts. A 2 by 4 that is 8 feet long is 5.33 board feet by its nominal size and 3.5 by its actual size.
A worked example
A board 1 inch thick, 6 inches wide and 8 feet long is 1 times 6 times 8 over 12, which is 4 board feet. Five of them are 20 board feet, or 1.67 cubic feet. A board 2 inches thick, 6 wide and 8 feet long is 8 board feet, and a piece of 3 by 4 inches and 12 inches long is 1.
Ten boards of 8/4, 7 inches wide and 8 feet long, are 9.33 board feet each and 93.33 in all. At $9.50 a board foot that costs $886.64, which is 93.33 times $9.50.
What it leaves out
The calculator counts the size you give it and adds nothing for cuts, defects or waste. It does not know how a lumberyard rounds a piece, whether to a tenth, a quarter or a whole board foot, so ask the seller.
Sources
- Ohio State University Extension, fact sheet F-35-02, Measuring Standing Trees, read on 2026-11-02.
- 7 CFR 1217.4, Board foot (Softwood Lumber Research, Promotion, Consumer Education, and Industry Information Order), read on 2026-11-02.
- USDA Forest Products Laboratory, General Technical Report FPL-GTR-118, Drying Hardwood Lumber (2000), read on 2026-11-02.
- Southern Pine Inspection Bureau, Nominal vs. actual lumber sizes, read on 2026-11-02.
Questions
How many cubic inches are in a board foot?
144. A board foot is a board 12 inches long, 12 inches wide and 1 inch thick, and any piece with the same volume is one too, such as 3 by 4 inches and 12 inches long.
How do I calculate board feet?
Multiply the thickness in inches by the width in inches by the length in feet, then divide by 12. A board 2 inches thick, 6 inches wide and 8 feet long is 8 board feet.
What does 4/4 or 8/4 lumber mean?
Hardwood thicknesses are named 4/4, 5/4, 6/4, 8/4 and so on. The top number over 4 is the thickness in inches: 4/4 is about 1 inch, 5/4 about 1 1/4, 6/4 about 1 1/2 and 8/4 about 2. The Forest Service lists them as 25, 32, 38 and 51 millimeters.
Do I use the nominal or the actual size?
Use the size your seller counts, and ask if you do not know. For softwood lumber 1 inch or more thick, a federal rule counts the nominal thickness and width and the actual length. A 2 by 4 that is 8 feet long is 5.33 board feet by its nominal size and 3.5 by its actual 1 1/2 by 3 1/2 inches.
How many board feet are in a cubic foot?
12. A board foot is 144 cubic inches, and a cubic foot is 1,728, so a board foot is a twelfth of a cubic foot.
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