Post Hole Concrete Calculator
The Post Hole Concrete Calculator estimates how many bags of concrete you need to set posts, accounting for the post's own volume displacing space in the hole.
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How This Tool Works
Enter your hole's diameter and depth, your post's width, and the number of posts to calculate total bags of concrete needed.
Formula & Method
Concrete volume = hole volume (π × radius² × depth) minus post volume (π × radius² × depth), converted to cubic feet, then divided by bag yield.
Example Calculation
A 12 inch diameter hole, 24 inches deep, with a 4×4 in post, needs about 1.4 cubic feet of concrete per hole — roughly 3 bags of 60 lb concrete.
Frequently Asked Questions
How deep should a fence post hole be?+
A common rule is to bury one-third to one-half of the post's above-ground height, with a minimum depth of 24 inches for most residential fences.
Do I need to subtract the post's volume?+
Yes — the post itself displaces concrete, so subtracting its volume gives a more accurate bag count instead of over-ordering.
Should I add gravel at the bottom of the hole?+
Many installers add a few inches of gravel at the bottom for drainage before pouring concrete — factor that into your hole depth if you plan to do this.
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