Post Hole Concrete Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
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Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the hole diameter and depth (mm).
- Optionally enter a square post size and the number of holes.
How it works
Hole volume = π × radius² × depth. If you enter a post size, its volume is subtracted from each hole.
Worked example
300 mm × 600 mm hole. ≈ 0.042 m³ of concrete per hole.
Common mistakes
- Forgetting the post displaces concrete — enter the post size to subtract it.
- Not ordering extra for spillage and uneven holes.
Frequently asked questions
How many bags is that?
A 20 kg bag of pre-mix yields roughly 0.01 m³, so ~0.042 m³ is about 4 bags per hole — check the bag's stated yield.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.