Sonotube Concrete Calculator
Four 10" tubes at 4 ft each take 16 × 80 lb bags, the deck-footing set the form opens on: 2.18 ft³ per tube, 4 bags apiece once 5% waste is in. Diameter × height × how many tubes → bags. Fill each tube in a single pour.
Bag counts are rounded up. Yields per bag: 80 lb → 0.60 ft³ · 60 lb → 0.45 ft³ · 50 lb → 0.375 ft³ · 40 lb → 0.30 ft³ (check your bag's printed yield).
Bags per tube, at a glance
| Diameter | Volume per ft | 80 lb bags per ft | 80 lb bags for 4 ft tube (+5%) |
|---|---|---|---|
| 8" tube | 0.35 ft³ | 0.6 | 3 |
| 10" tube | 0.55 ft³ | 0.9 | 4 |
| 12" tube | 0.79 ft³ | 1.3 | 6 |
| 16" tube | 1.40 ft³ | 2.3 | 10 |
| 18" tube | 1.77 ft³ | 2.9 | 13 |
| 24" tube | 3.14 ft³ | 5.2 | 22 |
This tool is form-by-form: one diameter and height, however many tubes. Sizing footings for a whole deck instead? The deck footing calculator adds a flared bell-base option and a footings-by-deck-size chart. Bag yields and coverage are in the concrete bag yields guide. Convert total yardage across all tubes with the bags-per-yard tool. If total volume nears a yard across all tubes, price bags vs ready-mix before you schedule a mixing day.
Footing tips
- Depth: bottom of the footing goes below frost line; that's the whole point. Your building department will tell you the local number.
- Base: many codes want the tube flared or sitting on a wider footing pad in soft soils; a tube alone can punch into the ground under load.
- Rebar: 2–4 vertical #4 bars is cheap insurance in taller piers.
- Anchors: wet-set post bases or anchor bolts beat drilling later: set them while the top is workable, aligned with a string line.
FAQ
How many bags of concrete fill a sonotube?
Per foot of height: an 8" tube takes 0.35 ft³ (about 0.6 × 80 lb bags), a 10" tube 0.55 ft³ (0.9 bags), a 12" tube 0.79 ft³ (1.3 bags). So a typical 10" × 4 ft deck footing is roughly 4 × 80 lb bags including waste.
What size sonotube for a deck post?
Common practice: tube diameter ≈ 3× the post width: 10" or 12" tubes for 4×4 and 6×6 deck posts. Your local code sets the real requirements (frost depth, bearing area, sometimes a wider footing base like a Bigfoot form), so check before you dig.
Should I pour each tube in one go?
Yes. Fill each tube in one continuous pour, rodding or vibrating as you go to knock out air pockets, then set your anchor bolt or post base while it’s wet. A cold joint halfway up a structural pier is the kind of thing building inspectors fail.
Does the sonotube stay in the ground?
Below grade, yes; the cardboard just stays and eventually breaks down. Any exposed portion peels off after 24–48 hours for a cleaner look. What matters structurally is the concrete and its footing, not the tube.