Post Hole Concrete Volume and Bag Calculator

Calculate net concrete around a square post in a round hole using user dimensions, allowance, and current package yield.

How to use the calculator

1. Enter round hole diameter.
2. Enter square post width.
3. Enter concrete depth.
4. Enter identical holes.
5. Enter order allowance.
6. Enter yield per bag.

Methodology

Net concrete volume equals round-hole cylinder volume minus the square-post prism volume over the entered concrete depth, multiplied by hole count.

The calculator uses only visible project values. It contains no hidden structural table, opening limit, post-spacing recommendation, price feed, product yield or jurisdictional preset.

Worked example

The documented governing fixture produces 38 bags after the user enters the current product’s bag yield. Calculation steps preserve the unrounded geometry before whole-item ceilings.

Measurement and review

Measure clear boundaries rather than nominal overall dimensions. Record the origin of every project-approved spacing, product quantity, package yield and price. For a guard, deck support, fence support, footing or gate, confirm the full system with current plans, instructions and the responsible authority or professional.

Scope limits

• Hole diameter and depth are measurements or approved project inputs; frost, soil, uplift and embedment rules are not supplied.
• Bag yield comes from the current product documentation and concrete quantity is not footing design.
• BrowserPowerTools does not certify code compliance, structural capacity, purchasing availability or contractor pricing.

Frequent mistakes

• Allowing a calculator example to become a structural default.
• Measuring around rather than between defined boundaries.
• Counting the same end, gate or corner component twice.
• Treating arithmetic remainder as a usable cut plan.
• Treating a user-price subtotal as a complete quote.

FAQ

Does this calculator choose a safe spacing?

No. Any spacing or opening constraint is explicitly user supplied.

Does it reproduce a code table?

No. Copyrighted code and industry documents are linked for context only.

Is the result stored remotely?

No. Calculation values remain in the browser.

Why might this page be no-index?

A no-index safe subset can be technically useful while safety review, search-intent validation or competitive-quality work remains open.

References

The sources below support units and explain why structural or code values cannot be universal. They are not copied datasets.

Engine 1.0.0. Reviewed 2026-08-22.

References and further reading

These sources define or explain the calculation. Source editions and model limits are part of the result—not decorative citations.

1. NIST Guide to the SI, Chapter 8, National Institute of Standards and Technology; accessed 2026-08-22. COMMON-NIST-SI