Concrete & Masonry
Calculate net concrete around round posts in cylindrical holes, then round to common premix bag counts.
Change the defaults to match your project and the product you plan to buy.
Project result
See net concrete volume for all holes and whole 80 lb / 60 lb premix bag estimates.
Planning estimate only. Verify product coverage, package size, supplier specifications and project requirements before purchasing.
Choose the right tool
You know the diameter, depth and number of cylindrical post holes and need concrete volume/bags.
Use Fence Post to determine post spacing first; use Concrete Calculator for a rectangular slab or pad.
Methodology
π × radius² × depth × hole count
Converts entered inches to feet internally.
π × post radius² × depth × hole count
Subtracts the cylindrical post volume.
net volume × (1 + extra %)
Adds spill and irregular-hole allowance.
ceiling(planned volume ÷ bag yield)
Rounds to whole premix bags.
Measure hole diameter and depth at several locations when soil causes irregular excavation. Enter the post diameter for round posts; square posts need a separate displacement calculation. Record the dimensions you used and recheck any section that is irregular, tapered or interrupted before relying on the final quantity.
Footing dimensions depend on fence/deck loads, frost depth, soil and local codes. This calculator estimates material only and does not determine required hole dimensions. Compare the calculated target with the exact package, coverage and availability offered by the supplier, then round only at the final purchase step.
Reference
| Planning item | Starting point | Verify / adjust |
|---|---|---|
| 80 lb premix yield | ≈0.60 ft³ | Verify bag label. |
| 60 lb premix yield | ≈0.45 ft³ | Verify bag label. |
| Hole size | Site/code-specific | Calculator does not design footings. |
| Final order check | Use measured inputs | Confirm package size, supplier coverage and project conditions. |
Questions
Yes. Subtracting post displacement prevents counting concrete where the post occupies space.
The current formula assumes round posts; for square posts, use a more specific footing calculation.
No. Required depth is a design/code question; enter the depth already determined for your project.
Planning guides
Concrete & Masonry
Estimate concrete around fence or deck posts using hole diameter, depth and post displacement without treating every hole as a full cylinder.
Read guide →Estimate fence post count and actual spacing from fence run, gate openings and maximum post spacing.
Open calculator → Outdoor ProjectsEstimate panel bays and posts from fence run, panel width and gate openings; use Fence Post Calculator when maximum post spacing is the main constraint.
Open calculator → Concrete & MasonryEstimate concrete volume in cubic yards plus common premix bag quantities for slabs and pads.
Open calculator →