Lumber YieldsEstimating the amount of lumber in a log is done using a log scale. A log scale is a formula with two input variables: the length of the log in feet, and the diameter of the log in inches inside the bark at the smaller end. The output from the formula is a number that is an estimate of the number of boardfeet of lumber in the log.
A boardfoot is defined as 1" x 12" x 12" or 144 cubic inches of wood. A board 1 inch thick by 12 inches wide by 8 feet long contains 8 boardfeet. A standard 8' 2x4 contains 3.5 boardfeet. The formula to calculate the boardfeet in any given board is: (thickness in inches x width in inches x length in feet)/12. 

The International 1/4 Inch rule comes closest to estimating the lumber yield from a log sawn using a thinkerf band sawmill. Please keep in mind that all log scales assume good quality logs. Defects in logs, such as bend (sweep) or decay will reduce the amount of lumber produced.