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Post Hole Concrete Calculator

Work out the concrete for a set of post holes, allowing for the volume the post itself displaces.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.0.0

Market
Imperial · sales tax
0.98 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Concrete required

0.48 yd³

Check your inputs

Geometry with the post volume deducted. Bag yields are nominal and vary with the mix and how wet it is made.

Per hole
0.05 yd³
Bags required
37 bags
Post displacement deducted
0.08 yd³
Cubic yards
0.48 yd³
Approximate weight
1926.57 lb

For the dimensions entered, expect a concrete required of 0.36 m³. Of the working steps, post displacement deducted dominates at 0.06 m³. Note that number of posts sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Common practice: hole diameter three times the post width; embedment one third of the above-ground height, or below frost depth where that is deeper
  • IRC R403.1.4 requires footings below the local frost line — the governing figure where ground freezes

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Frequently asked questions

How deep should a fence post go?
A third of the above-ground height is the usual rule — a 1.8 m fence wants about 600 mm of embedment. Where the ground freezes, that rule is overridden by frost depth: the footing must sit below the frost line or heave will lift it, and no amount of concrete stops that.
Should concrete go all the way to the top of the hole?
Finish slightly proud and slope it away from the post so water runs off. A concrete collar that dishes toward the post holds water against the timber and rots it exactly where it matters. Some prefer a gravel base under the post so water drains rather than sitting in a concrete cup.
Is a wider hole better than a deeper one?
For wind, often yes. A fence post fails by rotating, and resistance to overturning grows with the diameter of the mass in the ground. For frost, depth is what matters and width does nothing. Which one governs depends on your climate.