Post Hole Concrete Calculator
Estimate concrete volume and bag count for cylindrical post holes, subtracting the volume occupied by a square post.
Enter your measurements and calculate.
Example
Ten 12-inch-diameter × 30-inch-deep holes around 3.5-inch square posts require roughly 17 cubic feet before allowances.
Sources & assumptions
- QUIKRETE — concrete calculator and bag estimating
- Sakrete — concrete slab quantity and bag-yield guidance
Last reviewed September 1, 2026. Defaults are starting points; product-specific inputs are editable wherever coverage varies.
Related tools
Common questions
Why subtract the post volume?
The post occupies part of the hole, so that space does not need concrete.
Does this tell me the required hole depth?
No. It only calculates volume from dimensions you provide.
Can I use it for round posts?
The current version subtracts a square post cross-section; for round posts use a conservative smaller post-width input or calculate separately.
Take this number one step further
Use the result as an input to a decision model that compares the next action rather than stopping at the calculation.