Spike's Calculators


Roy Log Rule

Spike VM

The Roy Log Rule, with results in board feet, was used by mills in Quebec, Canada. The results from this rule are fairly accurate for 14' and 16' logs but over scales slightly on the high end for smaller sized logs.

Board feet = (D-1)² * L ÷ 20
D = diameter small end of log measured inside the bark in inches
L = the length of the log measured in feet

Roy 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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