Concrete Calculator for Fence Post Holes
Estimate concrete volume and whole bags for round fence post holes after allowing for the post itself.
Formula
Planning estimate. Check product specifications and local requirements before purchasing.
Worked example: Fence Post Concrete Calculator
Measurements in this example
| Number of posts | 12 |
|---|---|
| Hole diameter | 30 cm |
| Hole depth | 80 cm |
| Post diameter | 10 cm |
| Bag weight | 25 kg |
| Waste allowance | 10 % |
Calculated quantities
| Volume | 0.664 m³ |
|---|---|
| Bags | 56 |
What to check
This calculation uses: Number of posts, Hole diameter, Hole depth, Post diameter, Bag weight, Waste allowance. It returns: Volume, Bags.
Count only posts that will be concreted and measure the actual hole, not the auger label alone.
Concrete is the cylindrical hole volume minus the part occupied by the post, repeated for every post and increased by allowance.
Bag count uses an approximate dry concrete density. Replace the bag weight and compare yield with the manufacturer label.
Soil, frost depth, wind exposure and fence height determine suitable footing size and require local judgement.
Use the units beside each field. The values in the worked example are starting inputs; replace them with your measurements and the specifications of your material.
Compare alternatives
Open a tool, enter your measured dimensions, then save an estimate. Keep another version if you want to compare products or allowances.