12 Inch Sonotube Calculator — Concrete Per Pier
Calculate concrete volume and bag count for 12-inch Sonotube piers — typical for heavier porch columns, pergola posts, and structural support applications.
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.
12-inch Sonotube piers carry the bigger residential loads — porch columns, attached deck beams in high-snow zones, pergola corner posts under heavy timber, and pier-and-beam foundation piers under accessory structures. The extra diameter doubles the concrete volume per foot of depth versus 10″, but adds the capacity required by IRC Table R507.3 for larger tributary areas.
This calculator returns concrete volume and bag counts for any 12-inch tube depth. For projects with multiple piers totaling over 1 cubic yard, ready-mix delivery typically wins on cost.
How to Pour a 12 Inch Sonotube Pier
Volume = π × (12 ÷ 24)² × Depth (ft) × 12 = 0.785 cu ft per foot of depth.
12″ Sonotube Bag Reference
- 3 ft deep: 2.36 cu ft ≈ 4 bags 80 lb
- 4 ft deep: 3.14 cu ft ≈ 6 bags 80 lb
- 5 ft deep: 3.93 cu ft ≈ 7 bags 80 lb
- 6 ft deep: 4.71 cu ft ≈ 8 bags 80 lb
- 8 ft deep (deep frost): 6.28 cu ft ≈ 11 bags 80 lb
Four or more 12″ piers at 5+ ft depth = order ready-mix. The short-load fee is roughly equal to the cost of 1 extra 80-lb bag.
Frequently Asked Questions
How much concrete fills a 12 inch sonotube?
Volume per foot of depth: π × (6/12)² = 0.785 cu ft/ft. A 4 ft pier = 3.14 cu ft (~6 bags 80 lb); a 5 ft pier = 3.93 cu ft (~7 bags 80 lb).
When do I need a 12 inch sonotube instead of a 10 inch?
12″ tubes are appropriate when (1) tributary load exceeds IRC Table R507.3 limits for 10″, (2) the post supports a beam or attached structure rather than just decking, (3) you're in a high-snow load zone (60 psf+), or (4) the project is in soil with low bearing capacity.
Do 12 inch sonotubes need a rebar cage?
For piers under load-bearing beams, attached deck stair stringers, or porch columns: yes. Use 4 vertical #4 bars tied with #3 ties at 12″ on-center, with 3″ concrete cover.
How deep does a 12 inch sonotube footing need to be?
Below local frost line plus 4 inches of crushed-stone bedding — usually 36–60 inches in the northern U.S. Adapt to local code; some jurisdictions require a deeper minimum for support of attached structures.
Should I bell out the bottom of a 12 inch sonotube?
A bell-bottom Sonotube spreads the bearing area at the base for soft soils. Use it where soil bearing capacity is questionable or specified by an engineer.
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 →