Sonotube Footing Calculator — Concrete Per Pier
Calculate concrete volume per sonotube footing for deck posts, piers, and porch columns. Returns cubic yards, cubic feet, and 60 and 80-pound bag counts.
Enter Dimensions
Depth below grade to bottom of footing
Results
Bags per Tube
5bags
Total Bags
20bags
Volume per Tube
2.18cu ft
Concrete volume for one tube
Total Volume
0.323cu yd
All tubes combined
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Sonotube footings are the standard for decks, porches, pergolas, and detached structure posts in North America. The cardboard form is set in a post hole, filled with concrete, and topped with a post anchor — yielding a clean, code-compliant footing in a single pour.
This calculator computes the concrete volume per footing and scales up by the total footing count. Bag-mix conversion uses the standard 60-lb (0.45 cu ft) and 80-lb (0.6 cu ft) yields.
How to Estimate Concrete for Sonotube Footings
Per-footing volume (cu ft) = π × (Diameter ÷ 24)² × Depth (ft) × 12. Multiply by footing count and convert to bags or cubic yards.
Quick Reference: Concrete per Footing
- 8″ × 4 ft deep: 1.40 cu ft ≈ 3 bags of 80-lb mix per footing.
- 10″ × 4 ft deep: 2.18 cu ft ≈ 4 bags of 80-lb.
- 12″ × 4 ft deep: 3.14 cu ft ≈ 6 bags of 80-lb.
- 12″ × 5 ft deep (deep frost): 3.93 cu ft ≈ 7 bags of 80-lb.
- 16″ × 5 ft deep (large pergola): 6.98 cu ft ≈ 12 bags of 80-lb — at this volume, ready-mix delivery is usually cheaper.
When to Switch from Bag Mix to Ready-Mix
One cubic yard = 27 cu ft. If the total project exceeds 1.5 cu yd (≈ 40 cu ft), the per-cu-yd delivered price typically beats bag cost — even with the short-load fee. For most 6-footing residential decks, bags win. For deep frost footings on a large deck or attached carport, call the ready-mix plant.
Frequently Asked Questions
What diameter sonotube do I need for a deck footing?
Most residential deck footings use 10-inch or 12-inch Sonotube. The exact diameter depends on the column load, soil bearing capacity, and local frost depth. IRC Table R507 publishes minimum footing diameters for typical deck spans.
How deep should a sonotube footing be?
Set the bottom of the footing below the local frost line — typically 30–48 inches in northern climates, less in the South. The Sonotube extends from the bottom of the hole up to a few inches above grade.
How much concrete for a 10 inch sonotube 4 feet deep?
Volume = π × (5/12)² × 4 = 2.18 cubic feet. That's ≈ 4 bags of 80-lb concrete mix or ≈ 5 bags of 60-lb. For 6 or more footings, ordering a small ready-mix delivery (1 yd minimum) usually costs less.
Do I need rebar in a sonotube footing?
For deck and pergola footings under typical residential loads, a single vertical #4 or #5 bar and a J-bolt or post bracket is sufficient. Heavier loads (cabin posts, retaining wall piers) need a tied cage — check engineered plans.
Can I pour multiple sonotubes from one bag mix?
Yes, but plan to mix all needed concrete within a 90-minute window so each footing receives fresh material. For more than 6 footings totaling over 1 cubic yard, order ready-mix delivery for time and quality.
Looking for the general calculator?
Calculate concrete volume and bags needed to fill Sonotube forms for deck posts and piers. Supports 6, 8, 10, and 12-inch diameter tubes at any footing depth.
Open the Sonotube Calculator: Bags Per Footing →