Why subtract the post volume?
The post occupies space inside the hole, so only the annular space around it is concrete.
MAXScanner calculator
Post Hole Concrete Calculator — Volume & Bags
Calculate concrete around round posts from hole diameter, post diameter, embedment depth and post count, then estimate bags.
Result
593.07 L concrete
0.5931 m³ for 10 hole(s)
30 bag(s) at 20 L entered yield.
Formula and worked example
Concrete per hole = π × (hole radius² − post radius²) × depth; total = per-hole volume × post count.
A 12 in hole around a 4 in round post, 3 ft deep, uses the annular volume rather than treating the whole hole as concrete.
Assumptions
- Post and hole are modeled as concentric cylinders.
- Bag yield is user-entered because product yields vary.
Last updated: 2026-09-16
Frequently asked questions
Can I use square posts?
This version models round post displacement; for square posts use the concrete volume as a conservative check or calculate square displacement separately.