A board foot is a unit of measurement for the volume of lumber in the United States and Canada. It is used to measure rough lumber or planed/surfaced lumber. A board foot equals the volume of a one-foot length of a board, one foot wide and one inch thick. It can be abbreviated as FBM, BDFT, or BF. A thousand board feet can be abbreviated as MFBM, MBFT, or MBF, while a million board feet can be abbreviated as MMFBM, MMBFT, or MMBF.

To calculate board feet, the basic formula is thickness x width x length / 12. For example, a 2 x 4 - 10 has 6.667 board feet: 2 x 4 x 10 / 12 = 6.667 Board Feet. Another way to quickly calculate board feet is to memorize the board feet in each lineal foot of standard dimensional material. For example, there is .667 board feet in 1 lineal foot of 2 x 4.

It is important to note that nominal lumber includes air space around the physical board when calculating board feet in some situations, while the true measurement of "board feet" should be limited to the actual dimensions of the board. For planed lumber, board feet refer to the nominal thickness and width of lumber, calculated on its size before drying.

In summary, a board foot is a unit of measurement for the volume of lumber, and it equals the volume of a one-foot length of a board, one foot wide and one inch thick. To calculate board feet, the basic formula is thickness x width x length / 12.