Measure, in feet and inches, the length, width and the thickness of each piece of timber for which the board-foot volume is to be calculated.
Convert the measurements to decimals by multiplying the inches component by 0.0833, the decimal equivalent of 1 inch.
For example, the decimal equivalent of 1 foot and 2 inches is 1. 1666 - 1 foot + 2 x 0.0833 = 1.1666 feet.
Determine the volume in cubic feet by using the formula volume = length x width x thickness. For example, the volume of a piece of wood 12 feet long, 1.1666 feet wide and 0.5 feet thick is 6.9996 cubic feet.
Convert to cubic inches by multiplying the result from Step 2 by 1,728, the number of cubic inches in one cubic foot.
For example, 6.9996 cubic feet is 12095.3088 cubic inches -- 6.9996 x 1,728 = 12095.3088.
Divide the number of cubic inches in the result from Step 3 by 144, the number of cubic inches in 1 board-foot. The result is the board-foot volume of the timber
For example, 12095.3088 divided by 144 = 83.9952, so the volume of the timber is 83.9952 board-feet.