The hoppus foot is named for Edward Hoppus who introduced this measurement in his manual of practical calculations printed 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 thereto, not as its inventor, but merely as its tabulator, for his popular 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% from cubic volume of a round log allowing for 21.5% waste.
Measure the length of the log in feet and the girth of the log at midlength.