How this calculator works
A board foot is a volume of wood 1 inch thick, 12 inches wide and 12 inches long: 144 cubic inches. The formula is thickness (in) × width (in) × length (ft) ÷ 12.
Rough-sawn hardwood is sold by quarter-inch thickness: 4/4 (“four quarter”) is 1 inch, 5/4 is 1¼ inches, 8/4 is 2 inches. Lumber yards calculate board feet from this rough size, before planing, so use the nominal thickness.
Multiply by the number of boards for the project total. Then add a waste allowance for knots, cracks, sapwood and offcuts: about 15% for clean stock and 20% to 30% for rougher boards or projects with many small parts.
Cost is the total board feet with waste × the price per board foot. Prices vary by species, grade and thickness, so use your supplier’s current list.
The metric figure converts board feet to cubic metres (1 board foot = 0.00236 m³) for comparing with metric suppliers.
Worked example
Six 4/4 boards, 8 inches wide and 8 feet long, at $9.50 per board foot
- Each board: 1 × 8 × 8 ÷ 12 = 5.33 board feet.
- Six boards: 32 board feet. With 20% extra for waste: 38.4 board feet.
- Cost: 38.4 × $9.50 = $364.80.
Questions people ask
How many board feet are in a 2x4?
Dimensional lumber is usually sold by the piece, but by nominal size an 8-foot 2x4 is 2 × 4 × 8 ÷ 12 = 5.33 board feet. Its actual planed size is 1½ × 3½ inches.
Why is my planed board thinner than 1 inch?
Rough 4/4 lumber is about 1 inch thick before planing. After surfacing on both sides (S2S) it is typically around ¾ to 13/16 inch, but it is still priced on the rough size.
How much extra wood should I buy?
Plan for 15% to 30% more than the finished parts need, depending on the wood’s quality and how much you have to cut around defects. Buying it all at once also keeps the colour and grain consistent.
How do I convert board feet to cubic feet?
Divide by 12. There are 12 board feet in one cubic foot.
Last reviewed October 2, 2026