The board foot is a unit of volume measurement used in reference to lumber in the United States and Canada. Other nations use different measuring system for their lumber and timber. The board foot consists of a piece of wood which is one foot square by one inch, 2,360 cubic centimeters for those using the metric system. The board foot applies to rough or unfinished lumber, not to dimension lumber which has been finished and planed, and will therefore be slightly smaller.

Understanding units of measurement used with lumber can get awfully confusing, because of the fact that wood shrinks as it is processed. As a result, the actual measurement can differ from the stated measurement, as many people have learned when they physically measure a piece of dimension lumber and realize that it is smaller than the stated dimensions. In the case of a board foot, it is important to remember that the measurement is applied before the lumber is finished.

This term is often turned into the acronym FBM, which stands for foot, board measure. As a method of shorthand, if measurements start to climb up into the thousands of board feet, an M is added to the acronym, as in 19 MFBM, which means “19 thousand board feet.” Another M turns the measurement into millions: 3 MMFBM is three million board feet.

One common application of the board foot measurement is in assessing the value of a tree or a stand of trees. Calculations can be used to determine how many board feet will be harvested, which in turn determines the value of the stand. It is not uncommon for the value of a single large tree to also be expressed in board feet, in part so that the person selling the tree knows how much lumber was extracted from the tree, and thus, how much she or he is owed.

Value of timber is determined by more factors than the board feet which can be extracted. The quality of the wood is also important. X amount of board feet from a single tree tends to be more valuable than the same amount from multiple trees. This is in part because because if the wood comes from a single tree, very large boards and sheets can be cut from it. It's also because the wood may be denser and of higher quality as a result of the age of the tree.