Sonotube Deck Post Calculator — Concrete Per Footing
Size and pour concrete piers for residential deck posts per IRC R507 tributary load tables. Returns tube diameter, depth, and bag count for each post.
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 deck footings are the standard for residential deck construction in the U.S. — the cylindrical cardboard form sits in the post hole, gets filled with concrete, and supports the deck post via an embedded post anchor. IRC R507 governs sizing, spacing, and depth.
This calculator returns concrete volume and bag count for any deck footing configuration. For thinner pergola or shade-structure posts, see the 8 Inch Sonotube Calculator. For load-bearing pier columns, use the 12 Inch Sonotube Calculator.
How to Pour Sonotube Deck Footings
Per Footing (cu ft) = π × (D÷24)² × Depth (ft) × 12. Total = Per Footing × Count × 1.05 waste. Bags 80 lb = ⌈Total ÷ 0.6⌉.
IRC R507.3 Deck Footing Sizing (simplified)
- Tributary area < 25 sq ft: 8 inch diameter footing OK for typical residential deck.
- Tributary area 25-50 sq ft: 10 inch diameter standard.
- Tributary area 50-75 sq ft: 12 inch diameter.
- Tributary area 75-100 sq ft: 14-16 inch diameter or engineered footing.
- Snow load > 40 psf: step up one size from base table.
Frequently Asked Questions
What diameter Sonotube for a residential deck post?
Per IRC Table R507.3, 10 inch diameter is the most common deck footing for spans up to 12 ft × 6 ft tributary area (72 sq ft) in moderate snow zones. 12 inch tubes are used for larger spans or heavier snow loads.
How deep should a deck post footing go?
Below the local frost line: 30-48 inches in northern climates, 12-24 inches in the South. Plus a 4-inch crushed-stone bedding pad below the bottom of the Sonotube.
How many footings does a deck need?
Depends on beam and joist layout. Typical 12 × 16 ft attached deck: 4-6 footings. Free-standing decks need 2 extra footings to replace the house-supported edge. Joist span tables (IRC R507.5) drive the count.
Should I bell out the bottom of the footing?
Bell-bottom Sonotubes (wider at the bottom) spread bearing load over a larger area — useful in soft soils. For typical stable soils with 1500 psf+ bearing capacity, straight tubes are sufficient.
Do I need a post anchor on top of the Sonotube?
Yes — embed a Simpson PB44/66 post base or equivalent before the concrete sets. Direct post-to-concrete contact is prohibited because moisture wicks into the post end-grain and causes rot.
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 →