Concrete planning tool
Plan a repeated set of equal post holes or Sonotube forms with per-hole volume, aggregate concrete, waste-adjusted ready-mix, and bag alternatives.
Project calculator
Use one count for holes or tubes that share the same diameter and depth.
Plan responsibly
This project may be subject to local permit, zoning, site, or structural requirements.
Local requirements control: Model-code references do not confirm the code edition, amendments, zoning rules, permit requirements, or site criteria adopted for your project.
Not a post-footing design: Form diameter and concrete volume do not establish load capacity, uplift resistance, lateral stability, anchorage, or structural adequacy.
Residential deck footings: The verified section concerns residential deck footings. It should not be applied automatically to roofs, porches, fences, signs, pole buildings, or other post-supported structures.
Source: ICC Digital Codes: 2021 IRC Section R507.3 · Reviewed 2026-08-24
Local requirements may differ. A model-code reference does not confirm the code edition, amendments, zoning rules, or permit requirements adopted where the project is located.
2021 IRC, Section R507.3: Residential deck footings. Source: ICC Digital Codes: 2021 IRC Section R507.3. Reviewed 2026-08-24.
Local requirements may differ. Verify the adopted code, amendments, zoning rules, and permit requirements with the local authority.
Methodology
Plan Otter converts one hole's diameter and depth to feet, uses the cylinder formula for per-hole cubic feet, multiplies by the whole-number hole count, divides the aggregate by 27 for cubic yards, and then applies waste before whole-bag alternatives are rounded up.
Count assumes every post hole or tube has the same diameter and depth. Calculate groups separately when dimensions differ, then combine supplier quantities carefully.
This tool totals concrete after you choose count and dimensions. Post loads, uplift, lateral forces, soil, frost depth, drainage, tube use, and local requirements determine the actual design.
Each hole or tube is treated as a full cylinder. The estimate does not subtract embedded posts or add over-excavation, flared bottoms, surface collars, or concrete above grade unless those dimensions are represented.
Worked examples
At 10% waste, the aggregate estimate is 0.77 yd³, or 35 80-lb bags; each hole is 2.36 ft³ before waste.
At 10% waste, the aggregate estimate is 1.37 yd³, or 62 80-lb bags.
Common questions
For a round hole, use π × radius² × depth after converting dimensions to compatible units. This calculator also multiplies that per-hole amount by count.
Yes, when each tube can be represented as a uniform cylinder with the entered inside diameter and filled depth. Follow the form manufacturer's instructions and project design.
Not in one calculation. Group equal holes together and calculate each group separately so per-hole and aggregate quantities remain transparent.
No. Each hole is modeled as a full cylinder. Subtracting embedded posts is not included because post shapes, placement, and actual displacement vary.
The footing calculator estimates one circular footing. This tool keeps a per-hole result and multiplies it by a repeated count for an aggregate post or Sonotube project.
Sources
Last reviewed: 2026-08-22
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