How Much Concrete for a Sonotube? Bags by Diameter and Depth
A round form holds π × radius² of concrete for every foot of height. A 12 inch Sonotube holds 0.79 cu ft per foot, so a 4 ft tube needs about 6 bags of 80 lb concrete with 10% extra. The concrete calculator has a round column mode for any size.
Concrete per Sonotube by diameter
The last three columns are for one 4 ft tube with 10% extra. Multiply the per-foot figure by your own depth.
| Tube diameter | Cu ft per foot | 80 lb bags per foot | 80 lb bags, 4 ft tube | 60 lb bags, 4 ft tube | Cu yd, 4 ft tube |
|---|---|---|---|---|---|
| 6 in | 0.20 | 0.3 | 2 | 2 | 0.03 |
| 8 in | 0.35 | 0.6 | 3 | 4 | 0.06 |
| 10 in | 0.55 | 0.9 | 4 | 6 | 0.09 |
| 12 in | 0.79 | 1.3 | 6 | 8 | 0.13 |
| 14 in | 1.07 | 1.8 | 8 | 11 | 0.17 |
| 16 in | 1.40 | 2.3 | 11 | 14 | 0.23 |
| 18 in | 1.77 | 2.9 | 13 | 18 | 0.29 |
| 24 in | 3.14 | 5.2 | 24 | 31 | 0.51 |
Volume grows with the square of the diameter, so a 12 inch tube holds more than twice what an 8 inch tube does.
Deck footings: totals for a whole deck
| Footings | Tube | Depth | 80 lb bags | Cubic yards |
|---|---|---|---|---|
| 6 | 10 in | 3 ft | 18 | 0.40 |
| 8 | 10 in | 4 ft | 32 | 0.71 |
| 9 | 12 in | 4 ft | 52 | 1.15 |
| 12 | 12 in | 4 ft | 70 | 1.54 |
Past about 1 cubic yard (45 bags), a short-load ready-mix delivery or a rented mixer starts to make sense. Hand-mixing 45 bags is a long, heavy day.
Tips for pouring Sonotubes
- Measure the depth that gets concrete. Include the part of the tube above ground, and leave out any gravel in the bottom of the hole.
- Bell footings: if your deck plan calls for a wider base (a "Bigfoot" style form), work out that cone separately and add it.
- Rod the concrete with a stick or rebar as you fill to remove air pockets, then set the post anchor while it's wet.
- Cut the tube off above ground once the concrete has cured, if you don't want it to show.
Frequently asked questions
How much concrete is in a 12 inch Sonotube?
0.79 cu ft per foot of height. A 4 ft tube holds 3.14 cu ft, so 6 bags of 80 lb concrete with 10% extra.
How many bags of concrete for an 8 inch Sonotube?
An 8 inch tube holds 0.35 cu ft per foot. A 4 ft tube takes 3 bags of 80 lb concrete, or 4 bags of 60 lb.
How many bags of concrete for a 10 inch Sonotube?
A 10 inch tube holds 0.55 cu ft per foot, so a 4 ft tube takes 4 bags of 80 lb concrete with 10% extra.
How deep should a Sonotube footing be?
Below your local frost line, which ranges from about 12 inches in the South to 48 inches or more in the North. Many deck codes also require a wider footing at the bottom; check with your building department.