Spike's Calculators


Hoppus Rule

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The hoppus foot is named for Edward Hoppus, who introduced this measurement in his manual of practical calculations, published in 1736.

It is plain to the most casual observer that this is a most primitive system and that "Hoppus," whoever he might be, succeeded in attaching his name to it, not as its inventor, but merely as its tabulator, for his famous work is nothing but a ready-reckoner, compiled after the manner of the old road-books of the coaching days, for carrying in the pocket. (The Journal of the Society of Estate Clerks of Works, 1898).

Hoppus feet are calculated at 78.5% of the cubic volume of a round log, allowing for 21.5% of waste.

Circumference of Log Measured Mid Length
Length of Log ft
Log Circumference in


Log Volume in Hoppus Feet: hft
Converting Hoppus Feet to Board Feet: bf
True Log Volume in Cubic Feet: ft³


  1. enter the length of the log in feet
  2. the circumference of the log at midlength in inches


  1. the volume of the log in Hoppus's feet
  2. the Hoppus feet converted to board feet
  3. log volume in cubic feet


V = (G ÷ 4)² * L ÷ 144
V = volume in Hoppus feet
G = girth measured mid point of the log in inches
L = length of log in feet
The formula for cubic feet volume:
V = (G ÷ 4)² * L ÷ 113
one Hoppus foot (h ft) = 1.273239545 cubic feet (ft³)
one Hoppus foot (h ft) = 15.27887454 board feet (bf)

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