Does this determine footing size?

No. Footing dimensions, reinforcement, soil bearing and local requirements must be set by the responsible professional.

Excavation variation, placement loss and supplier ordering increments can make a net-volume-only order too small.

Concrete calculator

Concrete footing

Continuous footing volume, ready-mix quantity, and whole-bag equivalent.

Calculator result and formula

Ready-mix order: 1.25 yd³

Formula: Footing length × width × depth × quantity ÷ 27 × (1 + waste)

Formula ID: CONC-FOOT-001 · Version 1.0.0 · Published · Last reviewed Aug 26, 2026.

Inputs

Footing length: Finished continuous footing length Default: 20.
Footing width: Footing width before waste Default: 2.
Footing depth: Concrete depth/thickness Default: 8.
Number of footings: Count identical continuous footings Default: 1.
Waste factor: Allowance for placement, irregular excavation, and spill Default: 10.

How this calculator works

Use finished continuous-footing dimensions to establish concrete volume, then apply a visible waste allowance before supplier purchase rounding.

Measure the continuous footing length along its centerline.
Enter the actual width and concrete depth required by the approved design.
Use the rounded result as a starting point for a ready-mix supplier quote.

Worked example: Example: a 20 ft long footing, 2 ft wide and 8 in deep contains about 1.0 yd³ of concrete before a 10% allowance. The reviewed formula rounds the order to a quarter-yard purchase increment.

Assumptions and limitations

Footing geometry is treated as a continuous rectangle.
Ready-mix quantity is rounded to the next 0.25 yd³.
Bag and truck-load values are planning equivalents; confirm product yield and supplier delivery capacity.
Waste is applied before purchase rounding.

Common mistakes to avoid

Confirm the measurement basis and units before using the result.
Keep waste or allowance visible and adjust it for the actual job conditions.
Confirm supplier packaging, delivery increments, specifications, and final site requirements before ordering.

Calculator disclaimer

This planning calculator does not determine structural design, code compliance, installation requirements, or guaranteed pricing. Confirm final requirements with the appropriate responsible professional, authority, manufacturer, and supplier.

Formula review and sources

Internal QA complete · independent external review pending · Formula assumptions documented.

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