Hardwood lumber that we use for making cabinetry and furniture is sold by the board foot. This is a measurement that is constant through all thicknesses of lumber, rather than applying to "one-by", "two-by", etc.
In the example piece of lumber below, the measurement "A" would be the thickness in inches , measurement "B" the width in inches , and measurement "C" the length in feet .
Thus, the formula for calculating the board feet of lumber in our example would be..................
For example if the piece if lumber was
3 inches thick (A)
8 inches wide (B)
10 feet long (C), we would have
3 x 8 x 10 / 12 = 20 board feet.
Maintaining the proper units is important. Measuring width for example, in feet rather than in inches would result in an erroneous total. It is also important to note that this formula is generally used only for calculating the board foot quantity of "rough" lumber.
When lumber is first sold to a hardwood lumber supplier it is ususlly still in the "rough" state. This means that it has only been sawn with a band saw or other large dimensioning machine directly from the log, and has not yet been "planed" or smoothed down to the final useable thickness. Commonly this rough lumber will be planed to 25/32" thick, from an original blank that was about 1" thick in the rough. When we purchase the lumber at 25/32" thick (slightly larger than 3/4") we still pay for the full thickness of 1" that it was before it was milled (planed) down to the current state. Consequently, a piece of wood we receive that is only slightly over 3/4" thick, 12" wide and 1 foot long is still considered to be ONE BOARD FOOT, and is priced as such. If one feels cheated in this regard, the supplier will be happy to throw in the saw dust.