Board Foot Calculator

What a board foot is

A board foot is the standard unit lumber is bought and sold by in North America. One board foot is 144 cubic inches of wood — a piece 1 inch thick, 12 inches wide and 1 foot long. The formula is thickness in inches times width in inches times length in feet, divided by 12. A 1×8 that is 8 feet long is 5.33 board feet; ten of them are 53.3 board feet. Hardwood is usually priced per board foot, so this is the number that turns a cut list into a bill.

Nominal vs actual size

The trap in every board foot calculation is nominal sizing. A board sold as a 2×4 is actually 1.5 by 3.5 inches after surfacing, and a 1×8 is actually 0.75 by 7.25 inches. If you calculate with nominal dimensions you will overestimate the volume by roughly 25% on surfaced lumber. For rough-sawn lumber the nominal size is closer to reality, but it still pays to measure. Use the actual thickness and width in the calculator, not the size on the label.

How to use it

Enter the actual dimensions of one board and how many you need, then the price per board foot if you have a quote. The waste allowance covers defects, knots and cutting mistakes — 10% is a reasonable default for clear stock, and 15–20% is safer for lower grades. The total with waste is the number to order, and the cost line is what the order should come to before tax and delivery.

Frequently asked questions

How do you calculate board feet?

Multiply thickness (inches) × width (inches) × length (feet), then divide by 12. A 2-inch thick, 10-inch wide, 8-foot board is 2 × 10 × 8 ÷ 12 = 13.33 board feet.

How many board feet are in a 2×4×8?

Using nominal dimensions it is 5.33 board feet. Using the actual surfaced dimensions of 1.5 × 3.5 inches it is 3.5 board feet. Lumberyards price by the nominal board foot, so quote comparisons should use the same basis.

Why add a waste allowance?

Real boards have knots, checks, bow and saw kerf losses, and cut lists rarely use every inch. A 10% allowance is standard for good stock; rough or lower-grade lumber can need 15–20%. Ordering without it means a second trip to the yard.