Concrete Footing Calculator
Calculates concrete volume for cylindrical sonotubes (8", 10", 12", 16", 18" diameter) down to local frost line depths (36", 42", 48"), and continuous perimeter spread footings.
Formula
Single Pier Volume = π × (Radius ft)² × Depth ft; Total Cu Yds = (Piers × Single Vol) ÷ 27
1. Pier Radius ft = (Diameter in ÷ 2) ÷ 12 2. Pier Depth ft = Depth in ÷ 12 3. Cylinder Volume = π × Radius² × Depth 4. Base Adder = Has Bell ? 1.5 cu ft : 0 5. Total Volume (cu ft) = (Cylinder Vol + Base Adder) × Pier Count × (1 + Waste %) 6. Cubic Yards = Total Volume ÷ 27 7. 80 lb Bags = Ceil(Total Volume ÷ 0.60 cu ft)
Inputs
- Number of Footings / Piers
- Sonotube / Pier Diameter
- Footing Depth (Below frost line)
- Flared Bell Base / BigFoot Form?
Worked example
Pouring 6 structural deck footings below 42" frost line with flared plastic bell bases.
Outcome: Each cylinder is 2.75 cu ft + 1.5 cu ft bell = 4.25 cu ft per pier (25.5 cu ft total for 6 piers). Adding 10% waste equals 28.05 cu ft (1.04 cubic yards). Requires 47 bags of 80 lb concrete.
Why are flared bell bases (like BigFoot) recommended for deck piers?
A flared bell base spreads the vertical load over a wider footprint of subsoil (preventing sinking) and locks the bottom of the footing beneath the frost line to resist frost uplift.