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Concrete Footing Calculator — Strip, Pad & Pier Footings
Calculate continuous trench footings, rectangular pads, and round sonotube piers.
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Project Specifications
Cylindrical & Strip Footing Formulas
Transparent mathematical methodology explained in plain English.
Cylinder = π × r² × Depth | Strip = Length × Width × Depth For round sonotubes, volume is calculated using circle area times pier depth. Strip footings use trench cross-section times length.
Variables Explained:
- Radius r: Half of the sonotube diameter in feet.
Real Project Example
Six 12-inch Sonotube Deck Piers (4 ft deep)
Calculating concrete for deck frost footings.
Sample Project Inputs:
Quantity: 6 piers
Diameter: 12 inches (1.0 ft)
Depth: 4 ft
Waste: 10%
Step-by-Step Calculation:
- Radius: 12" ÷ 2 = 6" = 0.5 ft.
- Area per pier: π × 0.5² = 0.785 sq ft.
- Volume per pier: 0.785 × 4 ft = 3.14 cu ft.
- Six piers: 6 × 3.14 = 18.85 cu ft = 0.70 cu yd.
- With 10% waste: 20.74 cu ft = 0.77 cu yd (or 35 80-lb bags).
Calculated Answer: Order 0.8 cubic yards, or 35 80-lb pre-mixed bags.
Knowledge Base
Frequently Asked Questions: Concrete Footing Calculator
Click any question below to expand quick answers, formulas, and expert tips.
How deep must deck footings be dug?
Footings must extend below your regional frost line (typically 30" to 48" in northern climates) to prevent frost heaving from lifting your deck.