18 Inch Sonotube: How Much Concrete?
A 18 in Sonotube holds 1.77 cu ft of concrete per foot (π × r²). A 4 ft tube takes 7.1 cu ft: 12 bags of 80 lb or 16 bags of 60 lb Quikrete Concrete Mix. Sonoco's round-forms table lists 0.785 cu yd for a 12 ft column.
Concrete by tube length
| Tube length | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 2 ft | 3.5 | 0.13 | 6 | 8 |
| 3 ft | 5.3 | 0.20 | 9 | 12 |
| 4 ft | 7.1 | 0.26 | 12 | 16 |
| 6 ft | 10.6 | 0.39 | 18 | 24 |
| 8 ft | 14.1 | 0.52 | 24 | 32 |
| 12 ft | 21.2 | 0.79 | 36 | 48 |
Your tubes
Set up for: 18 in sonotubes · Different project?
Other sizes: 6 in · 8 in · 10 in · 12 in · 14 in · 16 in · 24 in · all sizes
FAQ
How many bags of concrete for a 18 inch sonotube?
2.95 bags of 80 lb Quikrete Concrete Mix per foot of tube, so 12 whole bags for a 4 ft tube and 48 for four of them.
Is a 18 inch sonotube big enough for my deck?
We don't size footings. The diameter and depth come from your deck plans, an engineer or your local building department; this page turns that size into concrete.
Sources
- Sonoco: Sonotube Builder's Tube concrete forms (concrete chart) · fetched and reviewed 2026-11-10
- Sonoco: Sonotube Round concrete forms brochure (concrete requirements table) · fetched and reviewed 2026-11-10
- Quikrete: QUIKRETE Concrete Mix (No. 1101) data sheet · fetched and reviewed 2026-11-10
Volumes only. ConcreteMath calculates volumes, bag counts, weights and your own cost figures. It gives no structural or engineering advice and never sizes footings, piers, slabs or rebar: those come from your plans, an engineer or your local building department. Bag counts are estimates from each maker's published yield; actual use varies with hole shape, uneven ground, waste and mixing. Bulk weights are published ranges; your supplier's figure wins.