Spike's Calculators


International 1/4-inch Log Rule (Clark) Calculator

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Calculate the amount of board feet in a log using the International 1/4-inch Log Rule online.

The International 1/8-inch Log Rule was developed by Judson F. Clark in 1906 while working for the Province of Ontario. In 1917 it was modified to allow for a 1/4-inch kerf. The International 1/4-inch Log Rule is considered to be the most accurate mathematical log rule for board feet calculation.


The first result listed is what the calculator is intended to calculate.

The conversions for the other volume measurements are derived from the first one.

Board Foot * 0.0833333 = Cubic Foot
Board Foot * 0.00235974 = Cubic Meter

Diameter Measured Inside Bark = DIB
Length of Log in Feet 4' Log 8' Log
12' Log
16' Log 20' Log
DIB of Log Small End in Inches in


All values are rounded to the nearest multiple of 5 board feet
and lengths over 20 feet are to be scaled as two or more logs.
Board Feet: bf
Cubic Feet: ft³
Cubic Meter:

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