Concrete planning tool
Estimate the concrete for one circular footing or pier from its finished diameter and depth, with waste-adjusted ready-mix and bag alternatives.
Project calculator
Measure the finished circular concrete footing, not the supported post.
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 an engineered footing design: Do not use a volume result to select footing width, thickness, depth, or reinforcement. Structural or geotechnical review may be necessary.
Footings: The IRC addresses residential footing design in relation to imposed loads, soil characteristics, and bearing on undisturbed soil or engineered fill.
Source: ICC Digital Codes: 2021 IRC Section R403.1 · 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 R403.1: Footings. Source: ICC Digital Codes: 2021 IRC Section R403.1. 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 the diameter and depth to feet, halves the diameter to find radius, applies the cylinder formula for cubic feet, divides by 27 for cubic yards, and applies the selected waste allowance before calculating whole-bag alternatives.
Enter the finished diameter and depth of the concrete footing itself. This tool does not subtract a post, bell shape, enlarged base, or embedded hardware.
Footing diameter and depth depend on loads, soil, frost depth, drainage, reinforcement, and local requirements. The calculator estimates material after dimensions are chosen; it does not design the footing.
The result reports both a waste-adjusted ready-mix volume and whole 40, 60, and 80 lb bag alternatives. Confirm delivery minimums and approximate bag yields with suppliers.
Worked examples
With 10% waste, one cylindrical footing needs about 0.22 yd³, or 10 80-lb bags.
With 10% waste, the estimated order is 0.51 yd³, or 24 80-lb bags.
Common questions
Convert diameter and depth to the same unit, divide diameter by two for radius, and use π × radius² × depth. Convert cubic feet to cubic yards by dividing by 27.
No. It estimates concrete for dimensions you provide. Loads, soil, frost depth, reinforcement, and local requirements determine design.
No. The footing is modeled as a full cylinder. Small embedded hardware is not subtracted, and irregular excavations require separate judgment.
Partial bags are not normally purchasable, so each bag alternative is rounded upward using the cited approximate mixed yield.
Waste can cover excavation variation, spillage, and ordering tolerance. Adjust the allowance to the project and supplier guidance.
Sources
Last reviewed: 2026-08-22
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