Material calculator
Post Hole Concrete Volume Calculator
Calculate the space around a round post inside a cylindrical hole.
Your measurements
Changing units changes the display, not the stored measurement.
Results
Example inputs
Your result will appear here
Enter the measurements and product details, then calculate.
These tools estimate material quantities from dimensions you choose. They do not specify structural depth or load capacity.
Enter the hole and the space occupied by the post
Enter the hole diameter, round-post diameter and depth to be filled. The form accepts diameters; the formula converts each to a radius by dividing by two. If a post occupies only part of the depth, represent the different sections separately instead of deducting it from the entire hole.
The round-post model assumes a cylindrical hole and a round post occupying the entered depth. It does not turn a square post into a circle with the same width. Use an appropriate measured displacement rather than a misleading diameter if the actual shapes differ.
Subtract the post volume
The difference between the circular cross-sectional areas is multiplied by depth. The post diameter must be strictly smaller than the hole diameter. Equal diameters leave no annular space, so the tool rejects them along with larger post diameters instead of presenting a usable concrete estimate.
Example: a cylindrical hole and round post
Enter a hole diameter of 0.30 m, a post diameter of 0.10 m and a filled depth of 0.6 m. The corresponding radii are 0.15 m and 0.05 m. Volume is π × (0.15² − 0.05²) × 0.6, or approximately 0.0376991118 m³. A group of identical holes multiplies that unrounded amount by the count.
For six such holes, the net volume is approximately 0.2261946711 m³. A chosen 10% allowance gives approximately 0.2488141382 m³. Round only the final purchasing quantity when a bag yield or other order unit is known.
Keep different holes in different groups
Use separate groups when hole size, post size or filled depth changes. Preserve those dimensions in the project so a later change does not accidentally alter every hole. The illustration explains the model; it is not a setting-out drawing.
Quantity only
PackLedge does not select hole depth, post spacing, footing size or a structure’s load capacity. All example dimensions are user-input examples. Obtain the specification for your project separately.
Frequently asked questions
Does the calculation include the volume occupied by the post?
No. In the round-post model, the post volume over the entered filled depth is deducted from the hole volume.
Can I use the same count for different hole sizes?
Create separate groups for different dimensions. Add their unrounded material requirements only after checking that their purchasing specifications match.
Sources and method
- PackLedge quantity methods
Original derivations using geometry, ratios, sums and whole-package rounding. Each calculator explains its assumptions and worked examples.
- NIST Guide to the SI — Conversion Factors ↗
Reference for unit conversions and clear identification of metric and customary units. Exact base-unit definitions are retained in calculations rather than rounded display factors.