Sonotube Pier Calculator — Concrete for Structural Piers
Estimate concrete for structural sonotube piers supporting beams, attached structures, or pier-and-beam foundations. Returns tube size, depth, and bag count.
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.
Structural sonotube piers are the workhorses of pier-and-beam foundations, attached porch and deck support columns, and light-commercial column footings. The difference between a pier and a deck post footing is in the load: piers carry concentrated loads from beams and columns above; deck post footings carry distributed deck loads through individual posts.
This calculator estimates concrete for any structural pier. For pure deck-post applications, see the Sonotube Deck Post Calculator.
How to Estimate a Structural Pier
Pier (cu ft) = π × (D ÷ 24)² × Depth × 12. Add separate footing concrete: typically 24 × 24 × 12 inch spread footing = 4 cu ft.
Structural Pier Reference
- 12 inch × 4 ft pier + 24×24×12 footing: 3.14 + 4 = 7.14 cu ft per pier ≈ 12 bags 80 lb concrete.
- 16 inch × 5 ft pier + 30×30×12 footing: 6.98 + 6.25 = 13.2 cu ft per pier ≈ 22 bags 80 lb — order ready-mix.
- 18 inch × 6 ft pier: 10.6 cu ft — definitely ready-mix territory.
- Rebar cage: 4 vertical #4 or #5 bars × pier height + #3 ties at 12 inch OC.
Frequently Asked Questions
What is a structural pier?
A structural pier is a tall, narrow concrete column embedded in the ground that transfers a concentrated load — beam, column, attached structure — down to bearing soil. Sonotubes are the cardboard forms used to shape these piers.
What size pier for a pier-and-beam foundation?
12 inch diameter is the residential minimum for pier-and-beam footings. 16 inch is common for taller crawlspaces or where the pier supports a continuous wood beam under heavy snow. Always confirm with engineered drawings.
Do piers need a footing?
Yes — for piers under load-bearing beams, the bottom of the Sonotube should rest on a poured concrete spread footing (typically 24×24×12 inch min) rather than directly on subgrade. This distributes load across more soil bearing area.
How is a pier different from a footing?
A footing is the wide base that spreads load onto soil. A pier is the vertical column above the footing. Many residential sonotube installations combine both: a bell-bottom Sonotube acts as integrated footing + pier in one pour.
What rebar in a structural pier?
For piers under load-bearing beams: 4 vertical #4 or #5 bars in a tied cage with #3 ties at 12 inch on-center, plus dowels into the footing. For light residential deck posts (not load-bearing): a single center bar is sufficient.
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 →