Concrete per Post Hole
The concrete a batch of post holes needs.
Example
You enter
- Number of post holes 16
- Hole diameter (in) 10
- Hole depth (in) 30
- Square post side (in, optional) 3.5
- Bag yield (cu ft) 0.45
You get
- Concrete per hole 1.151 cu ft
- Total (ft³) 18.41
- Bags 41
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeThe cylinder volume of each hole less the post's displacement, totaled and divided into bags. For a fence, deck, sign, or mailbox.
Formula or tablePer 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).
Source and editionCylinder-volume geometry less post displacement; bagged-concrete yields ~0.45 cu ft (60-lb) / 0.60 cu ft (80-lb).
Free accessBag yields free on the concrete-bag label.
What governsEstimate. AHJ and licensed professional govern.
API field namesnum_posts, hole_diameter_in, hole_depth_in, post_side_in, bag_yield_cuft, concrete_each_cuft, total_cuft, bags
- Bag yield ~0.45 cu ft (60-lb) / 0.60 cu ft (80-lb) mixed (editable)bagged-concrete labels