Select board feet, small-end inside-bark diameter, or log length to solve using the Scribner formula approximation. This is an estimate, not an official Decimal C table scale or guaranteed lumber yield.
Scribner Log Scale Formula
The following continuous formula approximates Scribner board feet. It is most consistent for logs 16 feet or shorter and under 28 inches in diameter; this calculator supports diameters of 6–40 inches.
Variables:
- V is the volume of the log (board feet)
- D is the small-end diameter inside bark (inches)
- L is the length of the log (feet)
Square the small-end inside-bark diameter in inches and multiply by 0.79. Subtract twice the diameter and 4, then multiply by the length in feet and divide by 16 to estimate board feet. This formula ignores taper and defects.
What is a Scribner Log Scale?
The Scribner Log Scale is a system used in the forestry industry to estimate the amount of lumber that can be yielded from a log. Developed by J. M. Scribner in the 19th century, the scale is based on diagrams of circles representing the cross-section of logs, with deductions made for saw kerf (the width of the cut made by the saw) and slabs. The scale is typically presented in the form of a table or rule, and is commonly used in the United States, particularly in the softwood lumber industry.
How to Calculate Scribner Log Scale?
The following steps outline how to calculate the volume of a log using the Scribner Log Scale formula.
- First, determine the small-end diameter inside bark (D) in inches.
- Next, determine the length of the log (L) in feet.
- Next, calculate 0.79 * D^2.
- Next, subtract 2 * D and 4 from the result from step 3.
- Next, multiply the result from step 4 by L.
- Finally, divide the result from step 5 by 16 to estimate board feet (V).
Example Problem:
Use the following variables as an example problem to test your knowledge.
Diameter of the log (D) = 12 inches
Length of the log (L) = 8 feet; estimated volume = (0.79 × 12² − 2 × 12 − 4) × 8 / 16 = 42.88 board feet.
