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 (2 x 4, 1 x 8, etc.). All of the boards of the same size in a stack at the lumberyard will be sold at the same price.
Calculating Hardwood Volume in Board Feet
With hardwoods, the story is quite different. Hardwoods are sold by the board foot, which is a calculation of the wood volume in the board. A board foot indicates a volume quantity equal to a board 12 inches by 12 inches by 1 inch, or one-twelfth of a cubic foot.
To understand how calculations are made, you must first understand the thicknesses of hardwoods offered by lumber retailers. Typically, board thicknesses will be listed in 1/4-inch increments:
- 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 example, a 10-inch-wide, 3/4-inch-thick board that measures 96 inches in length would come out to 5 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 6 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 appropriate 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 in the first example should be $90 (5 BF x $18 per BF = $90).
In the second example, the price for that board should be $108 (6 BF x $18 = $108).
How Volume Translates into Price
It's important to verify the price per board foot 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 combined BF prices for the three boards.
When shopping for hardwoods, don't be afraid to challenge the retailer's 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, the practice of rounding up, even by a small amount, can cost you plenty in the long run.
Buying by the board feet also brings up another consideration that doesn't arise when buying dimensional lumber. Two boards of the same material may both measure the same in terms of board feet volume, but they are very different in terms of size when comparing the two boards visually. For instance, a board that is 10 feet in length, 6 inches in width and 1 inch thick is very different from a board that is 2 1/2 feet long, 4 inches wide, and 3 inches thick—even though both boards measure 5 board feet in volume. When buying hardwoods, find boards that will meet your needs, and then measure them individually to calculate the price.