REPRINT FROM THE INTEGRAL NEWSLETTER
“A unit of board measure is the cubic content of a piece of wood one foot square and one inch thick.”
The definition of a board foot is simple. It is a piece of lumber that is 12 inches by 12 inches by 1 inch, or one twelfth of a cubic foot. The formula for calculating board feet is Thickness (in inches) times Width (in inches) times Length (in feet).
However, especially when dealing with large quantities, that entire math can become daunting. Fortunately, there are several board foot calculators available online. Once you understand how to covert conventional dressed dimensional lumber in all shapes and sizes, find one on line that suits you and place a shortcut to it on your desktop.
Dimensional lumber is sold by the board foot (abbreviated BF, MBF, or Bd. Ft.), and it is the accepted standard in the U.S. and Canada. When completing a take-off or purchasing at a lumber yard, you need to be aware that the numbers may have been rounded to make calculations easier. That is why it is always a good idea to check the lumber yard’s measurements and make sure you are actually getting the amount of wood that you need. Also keep in mind that the nominal dimension (1” x 4”, 2” x 4”, etc.) is not the actual dimension of the lumber. You will need to add or get a little extra depending on if you are estimating for a plain building or an irregular designed or detailed building.
Also, when calculating for lumber, keep in mind that you will almost definitely generate some waste. It is a good idea to increase amounts by 5 – 10 percent depending on the complexity of the design and size.
Here are some common lumber dimensions, and their equivalent board foot dimensions at lengths of one foot. If you are using one of these dimensions, simply multiply the number of board feet by the length of your board:
|1” x 4” = 0.33
1” x 6” = 0.50
1” x 8” = 0.67
1” x 10” = 0.83
1” x 12” = 1.00
|2” x 4” = 0.67
2” x 6” = 1.00
2” x 8” = 1.30
2” x 10” = 1.67
2” x 12” = 2.00
For example, if you have 10 linear feet of 1” x 4” lumber, you have 0.33 x 10 Bd. Ft., or 3.30 Bd. Ft. Remember, nominal dimensions are larger than the actual measurement of the board, so the board foot measurement includes empty air around the board. You will need a little extra lumber if precise dimensions are necessary.