Circular Holes Volume Formula
Volume per hole = π × radius² × depth
Total Volume (mm³) = Volume per hole × Number of holes
Total Volume (m³) = Total Volume (mm³) ÷ 1,000,000,000
Related Resources
Hole Volume Calculator — Concrete for Post Holes & Piers
Calculate how much concrete or fill you need for post holes, pier footings, and round excavations. Enter diameter and depth for instant volume in cubic metres.
Frequently Asked Questions
How much concrete for a 450mm post hole?
A standard 450mm diameter post hole at 600mm deep requires approximately 0.095 cubic metres (95 litres) of concrete. One 20kg bag of pre-mix makes about 0.009m³, so you need roughly 10-11 bags per hole.
How deep should post holes be in Australia?
For standard residential fences, post holes should be one-third the total post length underground. For a 2.4m fence post, that means 800mm deep. For pergola posts or structural posts, follow engineering specifications — typically 600-900mm minimum.
Should I use rapid set or normal concrete for post holes?
Rapid set concrete is fine for fence posts and non-structural posts — it sets in 15-30 minutes so you can keep working. For structural posts (pergolas, carports, retaining walls), use standard N20 concrete for full strength.
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