Estimate the board feet of lumber for stair components from the piece dimensions and count.
A board foot is a volume of lumber 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). Lumber is often priced per board foot, so this converts your piece dimensions into board feet for ordering and budgeting.
A unit of lumber volume equal to a board 1 inch thick, 12 inches wide, and 1 foot long, or 144 cubic inches.
Multiply thickness by width by length in inches, then divide by 144. Multiply by the number of pieces for the total.
Use actual dimensions for an accurate volume (a 2x12 is actually 1.5 by 11.25 inches). Suppliers may price on nominal size, so check how your yard quotes.