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How to Calculate Board Feet

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While hardwoods and softwoods may look somewhat similar in size and shape in stacks at the lumberyard, the method for calculating the cost of each is quite different. Softwoods are dimensional lumber, meaning that they are cut into uniform sizes (2x4, 1x8, etc.). All of the boards of the same size in a stack at the lumberyard are going to be the same price.

With hardwoods, the story is quite different. Hardwoods are sold by the board foot, which is a calculation of the cubic size of the board. A board foot is 12 inches by 12 inches by 1 inch, or one-twelfth of a cubic foot.

To begin, one must first understand the thicknesses of hardwoods. Typically, board thicknesses will be listed in fourths:
  • 3/4 = .75 inch in thickness
  • 4/4 = 1.00 inch
  • 5/4 = 1.25 inches
  • 6/4 = 1.50 inches
  • 7/4 = 1.75 inches
  • 8/4 = 2.00 inches and so on...
The formula for calculating board feet is as follows:

(length x width x thickness)/144

All of the dimensions in this formula are in inches. For instance, a 10-inch wide, 3/4 board that measures 96-inches in length would come out to five board feet: (96 x 10 x .75)/144 = 5

In another example, a 6/4 board that is 8 inches wide and 6-feet long (72 inches) would be six board feet: (72 x 8 x 1.50)/144 = 6

If you know the board feet measurement of each board and you know how much the lumberyard charges per board foot, you can determine the cost for that board. For instance, if the two boards above were oak, and you know that the lumberyard charges $18 per board foot for oak, in the first example above, the cost for the board would be $90 (5 BF x $18 per BF = $90).

In the second example, the price for that board would be $108 (6 BF x $18 = $108).

It's important to verify the price per board when you buy or sell lumber, because some yards like adjust to round numbers. In other words, if you try to buy three boards of oak that measure out to 6.72 BF, 5.69 BF and 7.71 BF, the lumberyard might try to round each board up to 7, 6 and 8 respectively. This seemingly minor adjustment would end up costing you an additional $15.84 over the actual BF prices for the three boards.

When going to buy hardwoods, don't be afraid to challenge their measurements. It doesn't hurt to keep a small calculator in your pocket and calculate the prices to check their figures. Most lumberyards will calculate it properly, but as you can see, just a small rounding can end up costing you quite a bit in the long run.
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