BuildCalc Guides · Concrete
How Many Bags of Concrete for a Sonotube?
Sonotube footings are sized by diameter and depth — every inch of either changes the bag count noticeably. Here is the full chart for common sizes plus the cylinder math for any custom footing.
Bag count chart — 80 lb bags
All counts are for 80 lb bags (0.6 ft³ yield), include a 5 percent safety margin, and round up to whole bags. For 60 lb bags multiply by 1.33.
| Diameter | 36″ deep | 48″ deep | 60″ deep |
|---|---|---|---|
| 6″ | 1 | 2 | 2 |
| 8″ | 2 | 3 | 4 |
| 10″ | 3 | 4 | 5 |
| 12″ | 4 | 6 | 7 |
| 16″ | 7 | 10 | 12 |
Below the frost line is required — most of the US is 36 to 48 inches; northern climates push to 48 to 60.
The math
For a 10 inch diameter sonotube 4 feet deep:
- Cylinder volume = π × r² × h, with everything in feet. π × (5 ÷ 12)² × 4 = 2.18 ft³.
- Add waste. 2.18 × 1.05 = 2.29 ft³ with a 5 percent margin.
- Bag count = 2.29 ÷ 0.6 = 3.82 → 4 bags of 80 lb. For 60 lb bags: 2.29 ÷ 0.45 = 5.1 → 6 bags.
Tips for ordering and pouring
- Count footings, then tubes. A 12×16 deck typically uses 6 to 9 sonotubes depending on beam span. Multiply your per-tube bag count by the number of footings and add 1 to 2 extra bags for the total job.
- Order one extra sonotube. They come in 4 ft and 12 ft lengths. The longer tube can be cut down — but a tube cut too short is scrap.
- Vibrate or rod. A hand-vibrator or a 1/2 inch rebar worked up and down knocks out the air pockets that weaken the column.
- Strap before the concrete sets. Anchor brackets or J-bolts need to be set into wet concrete and held square until the pour cures.
Calculate for your own footing
The chart above covers standard sizes. For an off-spec diameter or depth — or to total the bag count across all the footings on a project — BuildCalc's round-column mode handles the cylinder math, multiple identical footings and live material cost.
Open the concrete calculator →FAQ
How many 80 lb bags fill a 10 inch sonotube 4 feet deep?+
About 4 bags. The tube holds 2.18 cubic feet of concrete, and an 80 lb bag yields 0.6 cubic feet — so 4 bags with a small safety margin. A 12 inch tube at the same depth needs 6 bags.
How deep should a sonotube footing be?+
Below the frost line for your area. In the southern US that is 12 to 24 inches; in the upper Midwest and Northeast it is 36 to 48 inches; in northern New England and most of Canada it is 48 to 60 inches. Above the frost line the footing will heave each winter and the structure above will rack.
What size sonotube for a deck?+
Standard residential decks use 10 or 12 inch sonotubes. 10 inch is fine for ground-level decks and short-span beams; 12 inch is the safer default for elevated decks and longer beam spans. Tubes go up to 18 inches for heavier loads.
Do you need rebar in a sonotube?+
Yes, typically one or two #4 vertical bars in the tube plus a saddle of #4 rebar through the bottom. The vertical bars tie into the post bracket or strap above. Without rebar the footing is brittle and the post connection has no real anchor.
Can I dry-pour a sonotube?+
No. Sonotube footings are structural — they need wet-mixed concrete vibrated or rodded for full consolidation. Dry-pouring (dumping bagged mix in and adding water on top) is for fence posts only, not load-bearing footings.
How much does a sonotube footing cost in concrete?+
For a typical 10 inch × 4 ft footing: 4 bags of 80 lb at $5 to $7 per bag = $20 to $28 in concrete per footing. A 12 inch × 4 ft footing is about 6 bags = $30 to $42. Multiply by the number of footings — a 12×16 deck typically needs 6 to 9.
Related guides
- How many bags of concrete for a fence post? — fence-post version of the cylinder math.
- How many bags of concrete for a 4×4 post? — fence-line vs. corner vs. gate post counts.
- How many deck boards for a 12×16 deck? — the rest of the deck materials, once footings are set.