A board foot is a measure of volume, not just length. One board foot is defined as a piece of rough lumber 1 inch thick, 12 inches wide, and 1 foot long. To calculate the board footage of any piece of lumber, multiply the nominal thickness in inches, the actual width in inches, and the length in feet, then divide by 12.
A woodworker needs 10 boards of 8/4 walnut. The supplier's boards average 6 inches wide and 8 feet long, priced at $6.50 per board foot. (Note: 8/4 lumber has a nominal thickness of 2 inches).
First, calculate the volume of a single board: (2 × 6 × 8) ÷ 12 = 8 board feet. Multiply by the quantity of 10 to find the total volume: 80 board feet. Finally, multiply by the unit price: 80 × $6.50 = $520.00 total cost.
Before placing a material order, confirm how your supplier measures and bills for lumber.
- NOMINALBoard footage is calculated on the rough, nominal thickness. 4/4 lumber is calculated as 1 inch thick, even if it has been surfaced down to 13/16".
- WASTEThe calculation gives you raw volume. You must over-order by 10% to 30% depending on the grade (e.g., FAS vs. #1 Common) to account for knots, sapwood, and milling loss.
- WIDTHSHardwood is rarely sold in exact, uniform widths. When buying random width lumber, suppliers will tally the total board footage rather than counting identical boards.