How the fence post concrete calculator works
Enter the number of posts, hole diameter, and hole depth. The calculator estimates the volume of cylindrical holes and converts the result to approximate bag counts.
Formula
Hole volume = π × radius² × depth
Total volume = hole volume × number of posts
Example
For 10 holes that are 12 inches wide and 24 inches deep, the calculated hole volume is about 15.71 cubic feet before any soil, post displacement, waste, or installation adjustments.
Assumptions and material notes
Bag yields vary by product. The displayed 80-lb and 60-lb bag estimates use planning yields and should be checked against the specific product label. A post occupying part of a hole can reduce the actual concrete volume.
Frequently asked questions
Does the estimate account for the fence post itself?
No. It uses the full cylindrical hole volume, so it can be conservative.
Why can bag counts vary by brand?
Concrete products have different published yields and mix characteristics.
Should I add extra concrete?
For purchasing, follow the product yield and allow for excavation variation and spillage.
Can I use decimal hole sizes?
Yes.
What hole size should I use?
Use the hole dimensions required by your post size, soil conditions, frost depth, and local installation guidance.
Related calculators
Fence Calculator · Post Hole Concrete Calculator
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.