How to use the board foot calculator
- Add one row for each size of board in your lumber list. Enter the thickness and width in inches and the length in feet.
- Enter the quantity of that size (leave it blank for one piece) and, if you know it, the price per board foot.
- Keep the 10% waste allowance or change it. It applies to the total board feet and the total cost.
- Read the board feet for every row, the total, and the cost. Use the table to compare each line of the order.
Formula
Board feet per piece = thickness in inches x width in inches x length in feet / 12
Board feet per row = board feet per piece x quantity
Total board feet = sum of the rows
Cost per row = board feet x price per board foot
A board foot is the volume of a board 1 inch thick, 12 inches wide and 12 inches (1 foot) long, which is 144 cubic inches. Dividing by 12 works because the length is entered in feet.
Worked example: an order of oak and walnut
Four oak boards, each 1 inch thick, 8 inches wide and 10 feet long: 1 x 8 x 10 / 12 = 6.667 board feet each, or 26.667 for the four.
Two walnut boards, each 2 inches thick, 6 inches wide and 8 feet long: 2 x 6 x 8 / 12 = 8 board feet each, or 16 for the two.
The total is 42.67 board feet, and with a 10% allowance 46.93 board feet.
At $6.50 for oak and $9.25 for walnut the cost is 26.667 x $6.50 + 16 x $9.25 = $173.33 + $148.00 = $321.33, or $353.47 with the allowance.
Nominal and actual sizes
Lumber is often named by a nominal size that is larger than what you actually get after milling, and it is commonly priced by the nominal size. Hardwood is often described by its thickness in quarters of an inch, so a 4/4 board starts at about one inch rough. This calculator does not guess any conversion. For a price, enter the dimensions your seller bills by. To find the true volume of wood you are carrying home, enter the measured size.
Why board feet at all
Board feet let you price boards of different sizes on the same scale, which is why hardwood suppliers and sawmills use them. Two boards with the same board feet contain the same amount of wood regardless of their shape. Dimensional construction lumber is more often priced per piece or per linear foot, so this tool is best for hardwoods, specialty boards and anything sold by volume.
Planning cuts
Board feet tell you what to buy, not how it will cut. Defects, knots and the shape of your parts all affect yield, which is why the waste allowance exists. If you are laying out boards for a deck, the deck calculator counts boards and joists from the deck size, and the fence calculator does the same for rails and pickets.
Assumptions and limits
- The dimensions you enter are the dimensions used. No nominal-to-actual conversion is applied.
- Each row has one size. Boards with a taper or a live edge should be measured at an average width.
- The waste allowance applies to the totals only and is an input you control.
- Prices are used exactly as entered. Delivery, milling fees, kiln drying charges and tax are not included.
- Rows without a price are listed but left out of the cost totals, and the result says so.
Frequently asked questions
What is a board foot?
It is a volume of wood equal to a board 1 inch thick, 12 inches wide and 1 foot long, or 144 cubic inches. It is a way to price lumber of different sizes on one scale.
How many board feet are in a 2x4 that is 8 feet long?
Using the nominal size of 2 inches by 4 inches by 8 feet, it is 2 x 4 x 8 / 12 = 5.33 board feet. If you enter the actual milled size, the result will be smaller.
How do I convert board feet to cubic feet?
Divide the board feet by 12. One board foot is 144 cubic inches, which is one twelfth of a cubic foot of 1,728 cubic inches.
How much extra lumber should I buy?
It depends on the board quality and the project, so the allowance is yours to set. Many woodworkers add a margin for defects and trimming, and this tool starts at 10 percent.
Can I enter thickness in quarters like 4/4 or 8/4?
Enter the thickness in inches. A 4/4 board is 1 inch and an 8/4 board is 2 inches, which you can write as 1.25 for 5/4 or 1.5 for 6/4.