Spike's Calculators


Ontario Log Rule

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The Ontario Log Rule is a method used in the forest industry to measure the volume of a log in board feet. It applies to logs with diameters from 4" to 40" (measured small end, inside bark) and lengths of the log from 8' to 18'.

Board feet = (0.55D² - 1.2D) * L ÷ 12
D = diameter small end inside bark in inches
L = length of log measured in feet

Log lengths are measured in full feet.
Small end diameters of the log are measured inside the bark and recorded in one-inch diameter classes and rounded off to the nearest inch

Ontario Log Rule

Length of Log in Feet ft
DIB of Log Small End in Inches in


Board Foot fbm


  1. enter the log length (in feet)
  2. diameter small end measured inside bark (in inches)


  1. board foot of the log (fbm)
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