Concrete Calculator for Post Holes
Use this post-hole concrete calculator for repeated cylindrical holes where slab calculators are not the right shape.
Build the Estimate
Measurement controls, project presets, and a material result card for this calculator.
Formula and Assumptions
Hole volume = pi x radius squared x depth. Multiply by number of holes and divide by bag yield.
- Hole diameter and depth should be measured after digging.
- Local codes may require specific depth below frost line.
Worked Example
- 8 holes
- 10 inch hole diameter
- 30 inch hole depth
- 0.45 cubic ft per 60 lb bag
Each cylindrical hole is about 1.36 cubic feet. Eight holes require about 10.9 cubic feet before dividing by bag yield.
At 0.45 cubic ft per 60 lb bag, the post holes need about 24.2 bags, so plan on 25 bags plus site margin.
Measurement Tips
- Measure actual hole diameter after digging because augers often widen holes.
- Measure concrete depth, not the total post length.
- Count every repeated hole before converting to bags.
Buying Notes
- Use 40, 60, or 80 lb bag yield from the product label.
- Buy extra when soil walls crumble or holes bell out at the bottom.
Common Mistakes
- Using slab volume math for cylindrical holes.
- Estimating one hole correctly but forgetting to multiply by the number of posts.
Frequently Asked Questions
Is this concrete calculator for post hole exact?
No. It is an estimate based on common project formulas and the assumptions shown on the page. Always confirm package labels and local conditions before buying materials.
Should I add extra material?
Most projects need extra material for cuts, waste, damaged pieces, uneven surfaces, or future repairs. The calculator includes a waste factor where it matters.
Can I print the result?
Yes. Use the print action on the page to keep a simple copy of the inputs, formula, and estimated material list.