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 the quick-select buttons for common sonotube sizes, or tap a preset below to load a typical layout. Optionally add a flared bell footing at the base. Output drives concrete order: number of 60/80 lb bags for small pours, or yd³ delivered for larger jobs.
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 |
|---|
How to Calculate Concrete for Piers and Sonotubes
Deck footings, fence posts, porch piers and pole-barn columns are usually poured into cardboard sonotube forms or square box forms. The volume of a round shaft is a simple cylinder, so over-ordering by even one bag per hole adds up fast across a footing layout. Set the shape, enter the form diameter (or square side) and the hole depth, and the calculator returns cubic yards, 60 lb and 80 lb bag counts, weight and cost per the same takeoff method a foundation crew uses on site.
Depth should reach below the local frost line — most northern US jurisdictions require 36 in to 48 in per the IRC frost-protection provisions, and your building department publishes the exact figure. A 5–10% waste allowance covers form over-fill, spillage and slightly oversized augered holes; bump it toward 15% on hand-dug holes that bell out. For continuous footings instead of isolated piers, use the strip footing calculator or the spread footing calculator; for a tied grid of piers under a slab, the grade beam calculator handles the connecting beams.
Formulas
Round pier: V = π × (d/2)² × h. Square pier: V = s² × h. Bell footing (frustum): V = (π × h / 3) × (R² + R·r + r²) − π·r²·h, where R = flare radius and r = pier radius (the overlapping shaft volume is subtracted so it is not double-counted). Volume converts at 1 yd³ = 27 ft³. An 80 lb bag yields about 0.6 ft³ (0.022 yd³) and a 60 lb bag about 0.45 ft³ (0.017 yd³). Concrete density is taken as 150 lb/ft³ (≈4,050 lb/yd³).
Reinforcement per ACI 318-19
Pick vertical bars #3 through #6 with 2–6 bars per pier plus horizontal ties. Each vertical runs the full hole depth plus a 6 in embedment into the cap or footing above; lap splices, when needed, follow the ACI 318-19 development rule of roughly 40·db. For larger reinforced caps over pile groups, cross-check the pile cap calculator. Bulk bag-versus-truck pricing for the same pour can be compared with the concrete bag calculator, and flatwork tied to these piers with the concrete slab calculator.
Frequently Asked Questions
How deep should piers be? Below the frost line. Common depths run 36 in to 48 in in northern US states; warmer regions allow shallower. Always confirm the code-mandated frost depth with your local building department.
When should I add a bell footing? When soil bearing capacity is low or column loads are high, a flared (belled) base spreads the load over more soil. Typical bell diameters are 1.5× to 2× the shaft diameter; the calculator subtracts the overlapping shaft so the frustum volume is not double-counted.
Bags or ready-mix? Bagged concrete is practical up to roughly 1 yd³ total; beyond that, short-load or full ready-mix delivery is usually cheaper per yard and far less labor. Toggle the cost section between 60/80 lb bags and ready-mix to compare.
On pour day
Three things crews forget when pricing piers. Short-load fees — most ready-mix plants charge $80–150 when you order under ~3 yd³, so a deck with 6 piers at 12 in × 4 ft (≈0.45 yd³) almost always costs less in 80-lb bags. Bell over-dig — auger flares dig wider than the form, so add 10–15% waste, not 5%, on any hole with a flared base. Vertical bar projection — verticals must stick out above grade enough to lap into the post base, column or beam above (typically 6–12 in plus a 40·db splice per ACI 318-19 §25.5), so order bars at depth + projection, not just the hole depth. Typical 2025 USA prices: $5–8 per 80-lb bag, $150–220 per yd³ delivered (short-load surcharge below 3 yd³), $1.00–1.40 per linear foot of #4 rebar. Save runs to History and export with the diagram as text, CSV, A4 JPG, or PDF — estimates are planning numbers, not a substitute for a structural drawing.
