Post-hole concrete is the volume of the hole minus the embedded post volume. Treat the hole as a cylinder, subtract the post prism or cylinder over the same concrete depth, multiply by quantity, then apply the selected mix yield and whole-bag rounding.
Concrete around a post equals cylindrical hole volume minus the embedded post volume over the concrete-filled depth. Calculate each hole type separately, multiply by quantity, then convert the total using the selected concrete mix yield.
Published: September 20, 2026
Last reviewed: September 20, 2026
Published by BuildYard. The guide reflects BuildYard's calculation methodology and editorial standards and does not replace project-specific professional advice.
Use radius squared times pi times concrete-filled depth for a round hole.
Use actual field dimensions because augered holes can differ from nominal bit diameter.
For a square post, multiply actual width by actual thickness by embedded concrete depth.
For a round post, calculate a smaller cylinder over the embedded depth.
Subtract post volume from hole volume for each hole type, then multiply by the matching quantity.
Do not subtract portions of the post below or above the concrete zone incorrectly.
Convert the total adjusted cubic feet using the selected packaged concrete yield.
A modest placement allowance can cover irregular holes and handling loss without changing the measured geometry.
Hole diameter and depth depend on load, soil, frost, post type, and local requirements.
The calculator estimates material only; it does not design the footing or post foundation.
Concrete Calculator estimates ready-mix concrete, bag mix, weight, and truck loads for general slabs, pads, walls, and rectangular pours.
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Open calculator →BuildYard geometric example using actual 3.5 × 3.5 in post dimensions.
| Step | Result |
|---|---|
| Hole cylinder | 1.963 cu ft |
| Square-post displacement | 0.213 cu ft |
| Net concrete per hole | 1.750 cu ft |
| Ten matching holes | 17.50 cu ft before allowance |
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Calculate concrete for post holes by cylinder volume, post displacement, bag yield, hole count, and waste.
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