Lumber Tally field notes

How to Calculate Board Feet

The board-foot formula, worked examples in inches and feet, and the mixed-unit and fractional cases that trip up a plain calculator.

A board foot is a unit of lumber volume, not length: one board foot is the volume of a board 1 inch thick, 12 inches wide, and 12 inches long — 144 cubic inches. Lumberyards commonly use it to price rough hardwood. Ask which measurement and billing rules your supplier uses.

The formula

With thickness and width in inches and length in feet:

board feet = (thickness × width × length) ÷ 12

With all three dimensions in inches, divide by 144 instead of 12. Both give the same answer; 144 is simply 12 (inches per foot) folded into the inches-only version. This is the same formula Parkerville Wood Products publishes for its own yard: length × width × thickness in inches, divided by 144.

Worked examples

Fractions and mixed units

Lumber tape measures read in sixteenths, and a lot of stock is metric. This calculator accepts decimals (6.25), fractions (3/4), and mixed fractions (5 1/2) in all three dimension fields. Pick inches, feet, millimeters, centimeters, or meters for each dimension — so a rough board measured in millimeters and a finished board measured in inches can sit in the same tally without you converting anything by hand.

Multiple boards of the same size

Enter a quantity on each row; the tally multiplies the per-board board feet by that quantity before it adds the row into the total. Ten identical 1×6×8 boards is 10 × 4 = 40 board feet, not 4.

See board feet vs. linear feet for when board feet is the wrong measure, and lumber thickness and the quarter system for help choosing between nominal and measured thickness for your purpose. Ready to tally your own list? Go to the calculator.