6 Inch Sonotube Calculator — Light Pergola & Trellis Footings
Estimate concrete for 6-inch Sonotube footings — typical for pergola posts, light trellis structures, and decorative columns. Returns bag count at any depth.
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.
6 inch is the smallest practical Sonotube size — suitable for light pergolas, garden trellises, mailbox posts, and shade-cloth structures. Not approved for residential deck footings (IRC R507 requires 8 inch minimum) but sufficient for non-structural decorative columns.
For deck and porch use, see the 8 Inch Sonotube Calculator.
How to Pour a 6 Inch Sonotube
V (cu ft) = π × (6 ÷ 24)² × Depth (ft) × 12 = 0.196 cu ft per foot of depth.
6″ Sonotube Bag Reference
- 2 ft deep: 0.39 cu ft = 1 bag 80 lb
- 3 ft deep: 0.59 cu ft = 1-2 bags 80 lb
- 4 ft deep: 0.79 cu ft = 2 bags 80 lb
- 5 ft deep: 0.98 cu ft = 2 bags 80 lb
- 6 ft deep: 1.18 cu ft = 2 bags 80 lb
Frequently Asked Questions
What can a 6 inch sonotube support?
Light pergolas, garden trellises, shade structures, mailbox posts, and decorative columns. Not approved for residential deck or porch posts — IRC R507 specifies 8 inch minimum for typical decks.
How much concrete fills a 6 inch sonotube?
0.196 cu ft per foot of depth. A 4 ft footing = 0.785 cu ft = 2 bags 80 lb. A 3 ft footing = 0.59 cu ft = 1-2 bags 80 lb.
How deep should a 6 inch sonotube go?
Below local frost line — 30-48 inches in cold climates, 12-24 inches in the South. For light pergola posts, 30 inches is typical regardless of frost depth.
Should I use rebar in a 6 inch sonotube?
Optional for light decorative use; a single #4 vertical bar is sufficient if you want extra rigidity. Tied rebar cages are not needed at this size for non-structural applications.
How big does the hole need to be for a 6 inch tube?
Dig 8-10 inches wide to leave 1-2 inches of annular space for backfill that holds the tube plumb. Plus 4 inches of crushed-stone bedding at the bottom.
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 →