The board-foot is a specialized unit of volume for measuring lumber in the United States. It is the amount of wood in a 12-inch long 1-inch-by-12-inch board (or 1 foot × 1 inch × 1 foot, about 30 × 2½ × 30 cm³), or the equivalent (144 cubic inches, 2.36 litres). Unfortunately, it is not truly a measure of volume, due to nominal and actual measures used in the lumber business. In addition, the definition is different for hardwood and softwood.

To be exact, for hardwood, the board footage is defined as:

BF 

= SM × T,

where

SM 

= L × W ÷ 12, rounded to the nearest whole number,

L 

the nominal length in feet, truncated (rounded down) to the nearest foot,

W 

the actual width in inches,

T 

the nominal thickness in inches.

For softwood:

BF 

= L × W × T ÷ 12, rounded to the nearest hundredth of a board foot,

where

L 

the nominal length in feet, truncated to the nearest even foot,

W 

the nominal length in inches,

T 

the nominal thickness in inches.