Concrete per Post Hole
The concrete a batch of post holes needs: the cylinder volume of each hole less the post's displacement, totaled and divided into bags. For a fence, deck, sign, or mailbox.
Formula and source
Per hole = pi x (dia/2)^2 x depth / 1728 - post_side^2 x depth / 1728; total = per hole x posts; bags = ceil(total cu ft / bag yield).
Cylinder-volume geometry less post displacement; bagged-concrete yields ~0.45 cu ft (60-lb) / 0.60 cu ft (80-lb).
Audience
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Posture
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