Concrete for an 18-inch Sonotube
An 18-inch round tube holds 1.767 ft³ of concrete per foot of depth. A 4 ft tube takes 13 bags of 80-lb mix or 18 bags of 60-lb mix, with 10% extra.
- Per foot of tube1.767 ft³
- 4 ft tube7.07 ft³
- 80-lb bags (4 ft, +10%)13
- 60-lb bags (4 ft, +10%)18
Concrete needed
7.78 cubic feet
0.288 yd³ · 0.220 m³ · includes 10% extra
You need about 7.78 cubic feet of concrete, or 13 bags of 80 lb mix.
Bags of premix
- 2640 lb bags
- 2150 lb bags
- 1860 lb bags
- 1380 lb bags
- —20 kg bags
- —25 kg bags
- Before extra0.26 yd³ (7.1 ft³)
- Weight of bags1,040 lb
- Per hole—
- Ready-mix costAdd a price per yd³
- Bagged costAdd a price per bag
One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.
Bagged mix makes sense at 0.29 yd³. A ready-mix truck for a load this small would usually come with a minimum-order or short-load charge.
Estimate only, not a quote or engineering advice. Disclaimer
An 18-inch tube is used for heavier loads, larger columns and bigger structures. Each foot of it takes almost three 80-lb bags.
Bags per 18-inch tube by depth
| Depth | ft³ exact | 80-lb bags | 60-lb bags | 50-lb bags |
|---|---|---|---|---|
| 2 ft | 3.53 | 7 | 9 | 11 |
| 3 ft | 5.30 | 10 | 13 | 16 |
| 4 ft | 7.07 | 13 | 18 | 21 |
| 5 ft | 8.84 | 17 | 22 | 26 |
| 6 ft | 10.60 | 20 | 26 | 32 |
The math
For several tubes, set the number of columns in the calculator: it totals the volume before rounding, which can save a bag or two over multiplying the per-tube count. If the tube sits on a wider footing pad, add that as a separate footing.
Planning all the piers of a deck? Measure each tube's depth: when the ground slopes, the tubes on the low side are taller and need more concrete.
Frequently asked questions
How many bags of concrete for an 18-inch Sonotube?
Each foot of a 18-inch tube holds 1.767 ft³. A 4 ft tube takes 7.07 ft³: 13 bags of 80-lb or 18 bags of 60-lb mix, including 10% extra.
How many cubic feet in an 18-inch Sonotube?
1.767 cubic feet per foot of length. Multiply by the depth in feet.
How much concrete for an 18-inch Sonotube 3 feet deep?
5.30 ft³, which is 10 bags of 80-lb or 13 bags of 60-lb mix with 10% extra.
Other tube sizes
Related
Sources
- QUIKRETE: Concrete Mix No. 1101 data sheet (Revised Oct 2022; checked Nov 11, 2026)