Sonotube Concrete Calculator: Bags per Tube by Diameter
A 12 in sonotube 4 ft deep holds 3.14 cubic feet of concrete, which is 6 bags of 80 lb mix with 10% extra.
Advanced options: waste, prices
NRMCA advises ordering 4 to 10 percent over the estimate.
Concrete needed (with 10% extra)
0.13 yd³
0.10 m³ · 3.14 ft³ before extra
Sonotube / column: 12 in × 4 ft. Small pour: premix bags make sense.
Premix bags
- 80 lb6
- 60 lb8
- 50 lb10
- 40 lb12
- Ready-mix cost
- $20
- Weight
- 471 lb
Full breakdown
| Volume before extra | 0.12 yd³ · 0.09 m³ |
|---|---|
| With 10% extra | 0.13 yd³ |
| Weight (150 lb/ft³) | 471 lb · 0.24 tons |
| Pallets of 40 lb (80 bags each) | 1 |
| Pallets of 60 lb (56 bags each) | 1 |
| Pallets of 80 lb (42 bags each) | 1 |
| Truckloads at 12 yd³ | 1 |
| Truckloads at 8 yd³ | 1 |
Bag counts round up, as Quikrete's own calculator does. Cost uses your prices; delivery and short-load fees are extra.
Key takeaways
- A 12 in sonotube 4 ft deep holds 3.14 ft³, or 6 bags of 80 lb mix with extra.
- Sonoco's Builder's Tube comes in 6, 8, 10 and 12 in diameters.
- A 4×4 post usually fits a 12 in tube (Quikrete's 3× rule).
- Deck footing size follows IRC Table R507.3.1.
How Much Concrete Does a Sonotube Hold?
A sonotube holds 3.1416 × radius² × height of concrete. A 12 in tube 4 ft deep holds 3.14 ft³ (0.089 m³), which is 6 bags of 80 lb mix with 10% extra. An 8 in tube of the same depth holds 1.40 ft³, or 3 bags.
What Is a Sonotube?
A Sonotube is Sonoco's brand of round cardboard form for pouring concrete columns, piers and footings. Sonoco's Builder's Tube comes in 6, 8, 10 and 12 in nominal diameters and in 4, 8 and 12 ft lengths; other round forms work with the same calculator.
Sonotube Concrete Formula
ft³ = 3.1416 × (Diameter (in) ÷ 24)² × Height (ft)
yd³ = ft³ ÷ 27Dividing the diameter in inches by 24 gives the radius in feet in one step. The 10% extra covers overfill at the top and concrete that spreads into the hole below the tube.
How Many Bags of Concrete per Sonotube?
Bags of 80 lb concrete per sonotube, with 10% extra and rounded up, are listed by diameter and depth. The math applies to any round form of that inside diameter.
| Diameter | 2 ft deep | 3 ft deep | 4 ft deep | 60 lb bags at 4 ft |
|---|---|---|---|---|
| 6 in | 1 | 2 | 2 | 2 |
| 8 in | 2 | 2 | 3 | 4 |
| 10 in | 2 | 3 | 4 | 6 |
| 12 in | 3 | 5 | 6 | 8 |
| 14 in | 4 | 6 | 8 | 11 |
| 16 in | 6 | 8 | 11 | 14 |
| 18 in | 7 | 10 | 13 | 18 |
| 24 in | 12 | 18 | 24 | 31 |
What Size Sonotube for a 4x4 or 6x6 Post?
A 4×4 post usually goes in a 12 in sonotube and a 6×6 post in an 18 in tube, using Quikrete's rule that the hole should be about three times the post's width. A 4×4 measures 3.5 in actual, so 3 × 3.5 = 10.5 in, rounded up to the next tube size; a 6×6 measures 5.5 in, so 16.5 in rounds up to 18 in. This size is derived from Quikrete's hole rule, not a Sonoco requirement.
How Many Sonotubes Do I Need?
You need one sonotube per post or pier in your plan. The deck or shed plan sets the count and spacing; for tubes of mixed sizes, add each size as a part in the calculator to get one total.
Bags or Ready-Mix for Sonotubes?
Bags suit sonotubes unless the total passes about 1 yd³, which is this calculator's own rule. Ten 12 in tubes 4 ft deep need 1.28 yd³ with extra, or 58 bags of 80 lb mix.
Worked Examples: Sonotubes for a Deck
Six 10 in tubes, 4 ft deep. 6 × 2.18 = 13.09 ft³; with 10% extra, 24 bags of 80 lb mix.
Nine 12 in tubes, 4 ft deep. 9 × 3.14 = 28.27 ft³; with 10% extra, 52 bags, or 1.15 yd³, close to the point where ready-mix makes sense.
One 16 in tube, 5 ft deep. 3.1416 × 0.667² × 5 = 6.98 ft³; with 10% extra, 13 bags of 80 lb mix.
How Deep Should a Sonotube Be?
A sonotube footing goes below the local frost line; the 2021 IRC requires piers to extend below the frost depth in Table R301.2 and exterior footings to sit at least 12 in below undisturbed ground (R403.1.4). Deck footing size follows IRC Table R507.3.1, on our deck footing calculator.
Bags per Foot for Each Sonotube Size
| Diameter | ft³ per foot | 80 lb bags per foot (with 10%) |
|---|---|---|
| 6 in | 0.20 | 0.36 |
| 8 in | 0.35 | 0.64 |
| 10 in | 0.55 | 1.00 |
| 12 in | 0.79 | 1.44 |
| 14 in | 1.07 | 1.96 |
| 16 in | 1.40 | 2.56 |
| 18 in | 1.77 | 3.24 |
| 24 in | 3.14 | 5.76 |
Sonotube Concrete Calculator FAQ
How many bags of concrete for an 8 inch sonotube?
A 8 in sonotube 4 ft deep takes 3 bags of 80 lb concrete or 4 bags of 60 lb, with 10% extra.
How many bags of concrete for a 10 inch sonotube?
A 10 in sonotube 4 ft deep takes 4 bags of 80 lb concrete or 6 bags of 60 lb, with 10% extra.
How many bags of concrete for a 12 inch sonotube?
A 12 in sonotube 4 ft deep takes 6 bags of 80 lb concrete or 8 bags of 60 lb, with 10% extra.
How many bags of concrete for a 16 inch sonotube?
A 16 in sonotube 4 ft deep takes 11 bags of 80 lb concrete or 14 bags of 60 lb, with 10% extra.
How many bags of concrete for a 24 inch sonotube?
A 24 in sonotube 4 ft deep holds 12.57 ft³ and takes 24 bags of 80 lb concrete with 10% extra.
How many bags of cement does it take to fill a sonotube?
A 12 in sonotube 4 ft deep (3.14 ft³) needs about 1 bag of 94 lb cement at 1:2:3 plus sand and gravel, or 6 bags of 80 lb premix.
Next step
Set the depth with your local frost line, then total all tubes as parts in the calculator and compare bags with ready-mix on bags or ready-mix.
Official sources
Last reviewed 2026-11-05. Numbers come from our tested engine; see how we calculate and our sources.