8 Inch Sonotube Calculator — Concrete Per Footing
Calculate concrete volume and bag count for 8-inch diameter Sonotube footings. Returns cubic feet and both 60 and 80-pound bag counts from 2 to 6 feet deep.
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.
8-inch Sonotube is the entry-level pier size — light enough to pour from bags, sufficient for pergolas, garden structures, and light-duty deck columns under modest tributary loads. At deeper depths, 8″ tubes are popular for pier-and-beam foundations beneath sheds and small accessory structures.
This calculator computes the exact concrete volume and bag count for any 8-inch tube depth. Bag conversions assume standard 60-lb (0.45 cu ft) and 80-lb (0.60 cu ft) yields.
How to Pour an 8 Inch Sonotube Footing
Volume = π × (8 ÷ 24)² × Depth (ft) × 12 = 0.349 cu ft per foot of depth. Multiply by total depth to get cubic feet.
8″ Sonotube Bag Reference
- 2 ft deep: 0.70 cu ft ≈ 2 bags 80 lb
- 3 ft deep: 1.05 cu ft ≈ 2 bags 80 lb
- 4 ft deep: 1.40 cu ft ≈ 3 bags 80 lb
- 5 ft deep: 1.75 cu ft ≈ 3 bags 80 lb
- 6 ft deep: 2.09 cu ft ≈ 4 bags 80 lb
For projects with 4+ piers totaling over 1 cu yd (27 cu ft), ready-mix delivery typically beats bag-mix cost even after the short-load fee.
Frequently Asked Questions
How much concrete fills an 8 inch sonotube?
Volume per foot of depth: π × (4/12)² = 0.349 cu ft/ft. A 4 ft footing = 1.40 cu ft; a 5 ft footing = 1.75 cu ft. Convert to bags: ~3 bags of 80 lb at 4 ft depth.
What can an 8 inch sonotube footing support?
Light residential loads: pergolas, garden trellises, light deck columns up to 50 sq ft of tributary area in low snow zones. Always verify with IRC Table R507.3 against your tributary load.
Should I use rebar in an 8 inch sonotube?
A single vertical #4 bar through the center is good practice for any 8″ footing under decking. Heavier residential loads (porch columns, attached deck stair stringers) warrant a 4-bar tied cage.
How deep does an 8 inch sonotube need to go?
Below the local frost line — 30 to 48 inches in most northern climates, 12–24 inches in the South. Plus 4″ of crushed-stone bed at the bottom.
Can I use a single 8 inch tube for a deck post?
Yes for light-duty pergolas and shade structures. For a full deck (people loads + furniture), most code prefers 10″ or 12″ tubes per IRC Table R507.3, especially in high-snow zones.
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 →