How the post hole concrete calculator works
Enter the number of holes, hole diameter, and hole depth. The calculator estimates cylindrical concrete volume and includes a 10% planning allowance.
Formula
Hole volume = π × radius² × depth
Order volume = total hole volume × 1.10
Example
Four 12 inch diameter holes at 24 inches deep require about 6.28 cubic feet of cylindrical volume before the 10% allowance.
Assumptions and material notes
The estimate does not subtract the volume displaced by a post. Actual concrete placement also depends on hole shape, soil conditions, and installation method. Check the concrete product's published yield before buying bags.
Frequently asked questions
Does this include a waste allowance?
Yes. The main result includes a 10% planning allowance.
Does it subtract the post volume?
No. It estimates the full cylindrical hole volume.
Can I use different hole sizes?
Calculate each hole size separately when your project has multiple sizes.
Are bag yields universal?
No. Always use the yield printed on your specific product.
How much extra should I order?
Use the displayed allowance as a planning aid, then consider excavation variation, spillage, and the supplier's product yield.
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Disclaimer: Estimates are for planning purposes only. Actual material requirements may vary based on site conditions, material specifications, installation methods, waste, and local requirements. Always verify quantities with your supplier or qualified professional before purchasing materials.