Fence Post Concrete Calculator
Enter the number of posts, cylindrical hole dimensions, and the concrete yield printed on one bag.
Scenario table
| Post count | Hole diameter (mm) | Hole depth (mm) | Yield per bag (L) | Volume per hole (L) | Total hole volume (L) | Bags per post | Total bags | Total bag yield (L) | Surplus yield (L) |
|---|
Frozen calculation report
A QUICK WALKTHROUGH
How to use this tool
- Enter a whole number of posts.
- Set hole diameter and depth in millimetres, plus yield per bag in litres.
- Review bags per post and the total, rounded up separately for each hole.
Cylindrical hole estimate
The hole volume is π × (diameter ÷ 2)² × depth. Divide that volume by the stated yield per bag, round up to a whole bag for each post, then multiply by the post count.
Full hole volume
The estimate does not subtract the post that occupies part of the hole, so it can overstate the concrete needed. Hole shape, soil, spillage, and product yield can also differ on site; check the package label and project conditions.
Local planning estimate
Calculations run in this browser. This tool estimates material quantity only; it does not set post spacing, foundation depth, structural suitability, or safe installation requirements.
Compare
Enter 1–20 values separated by commas, spaces or semicolons. Counts must be safe whole numbers ≥ 0; all dimensions and bag yields must be positive.
Frozen calculation report
Uses the binary approximation Math.PI and JavaScript numbers, not exact decimal π. Values near a ceiling boundary are unsupported. All reported numbers retain the complete Number representation. Units: diameter/depth mm; volume/yield L; count and bags whole numbers.
GOOD TO KNOW
Common questions
Does the result account for the post?
No. It uses the full cylindrical hole volume, which gives a small quantity buffer but may overestimate the fill.
Why round up for each post?
Each hole needs a whole bag under this estimate. Rounding the per-post amount before multiplying reflects that constraint.
Which bag yield should I use?
Use the volume stated for your exact concrete or post-mix product. Yield varies between products and package sizes.