Concrete Pier Calculator — ft to cu yd, bags, cost
How to use this calculator
Enter the number of piers, choose round (sonotube) or square shape, set the diameter or side length and depth. Use quick-select buttons for common sonotube sizes. Optionally add a flared bell footing at the base. Results update instantly with volume per pier, total volume, weight, and bag counts.
Cost — pick ready-mix delivery per yd3, 80-lb bags, or 60-lb bags to get the total material cost.
Reinforcement — vertical rebar per pier with ties, per ACI 318-19.
Labor — rate per pier, per yd3, or a flat price. Grand total sums all active sections.
Saved Calculations
| Time | Shape | Piers | Size | Depth | Vol yd³ | Bags | Cost | Total |
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How to Calculate Concrete for Piers and Sonotubes
This concrete pier calculator estimates volume in cubic yards, number of pre-mixed bags (60 lb and 80 lb), total weight, material cost, reinforcement requirements, and labor expenses for round sonotubes and square piers. Enter pier diameter or side length in inches with fraction precision, set the depth (standard: 36" for frost line, 42" standard, 48" deep frost), number of piers, and adjust waste allowance from 5% to 20%.
Formulas
Round pier: V = pi x (d/2)² x h. Square pier: V = s² x h. Bell footing (frustum): V = (pi x h / 3) x (R² + R x r + r²) where R = flare radius and r = pier radius. Volume is converted: 1 yd³ = 27 ft³. An 80-lb bag covers approximately 0.6 ft³ and a 60-lb bag covers approximately 0.45 ft³. Concrete density is approximately 150 lbs/ft³ (4,050 lbs/yd³).
Reinforcement per ACI 318-19
Choose vertical rebar #3 through #6 with 2 to 6 bars per pier, plus horizontal tie wire hoops. The calculator accounts for 3" cover at bottom and standard development length. Each bar extends the full pier depth plus 6" embedment into the footing or cap above.
Frequently Asked Questions
How deep should piers be? Piers must extend below the frost line, which varies by region. Common depths range from 36" to 48" in northern US states. Check local building codes for exact frost line depth requirements.
When to use a bell footing? A flared (bell) base is required when soil bearing capacity is low or when pier loads are heavy. The wider base distributes weight over a larger area. Typical flare diameters are 1.5x to 2x the pier diameter.
