Always remember, that a board foot is a volume measurement.  Linear dimensions of the board are simply a function that provide the formula for calculation.    Equal to 1/12th of a cubic foot, the board foot takes into account the actual thickness of the board.

Hardwood lumber is sold in thickness increments expressed in 'quarters', ranging from 4/4 through 12/4.  For example a 4/4 board, spoken as "four - quarter", is actually 1/16" thicker than the nominal thickness when rough sawn and kiln-dried.

In each dimension, the actual thickness allows for machining and finishing to a standard thickness.  This allows the wood worker to plane the lumber down to a usable finished thickness close to the nominal thickness (i.e. a 4/4 board would finish to 7/8" or 3/4").  The extra thickness also provides enough thickness to allow board straightening and grain selection.

Tallying is calculated based on the nominal thickness of the board.   (i.e. a 4/4 board is counted as being 1" thick).  At Loyalist Forest, we typically trim our lumber with 6" extra length over the stated length, but this is not included in the tally (i.e. a 9' board is actually 9'-6" long, but sold as a 9' board).

To calculate the board measure of a piece of hardwood lumber, use the following formula: 

Board footage = thickness (in inches)  x   width (in inches)     x   length (in feet)