Sonotube Concrete Calculator
A 12-inch Sonotube at 48 inches deep holds 0.12 cubic yards (3.14 cubic feet) — about 6 bags of 80-lb concrete mix per tube including 10% waste. Use this calculator for deck footings, fence posts, pier footings, and pergola columns. Enter diameter, depth, and quantity to get your exact concrete volume, bag count, and recommended ready-mix order.
Pro Tips
- →Sonotubes come in standard diameters: 8, 10, 12, 14, 16, 18, 24 inches
- →Buy tubes 6-12 inches longer than needed for cutting
- →Place tubes on gravel base for drainage
- →Backfill around tubes before pouring for stability
- →Remove cardboard tube after concrete sets (or leave in ground)
Includes 10% waste factor
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Cost Estimate
Estimated material costs for your project
Recommendation: Bagged Concrete
For smaller projects, bagged concrete gives you more control and less waste.
26 bags × 80lb
0.58 cubic yards + delivery
Prices vary by location and time. Contact local suppliers for accurate quotes.
For general step-by-step instructions, read our complete How To Calculate Concrete and How Many Bags.
How to Calculate Concrete for a Sonotube
A Sonotube is a cylinder, so its volume follows the formula for a cylinder: V = π × r² × height, where r is the radius (half the diameter). The trick is keeping units consistent. Diameter and depth are usually given in inches, but concrete is ordered in cubic feet (for bags) or cubic yards (for ready-mix).
The cleanest approach is to convert everything to feet first:
- Radius in feet = (diameter in inches ÷ 2) ÷ 12
- Height in feet = depth in inches ÷ 12
- Volume (cubic feet) = 3.1416 × radius² × height
- Cubic yards = cubic feet ÷ 27
For example, a 12-inch tube at 48 inches deep: radius = 0.5 ft, height = 4 ft, volume = 3.1416 × 0.25 × 4 = 3.14 cubic feet, or 0.116 cubic yards. Always add about 10% for waste, spillage, and the slightly uneven base at the bottom of the hole. For the underlying math applied to any shape, see our how to calculate concrete guide, or jump straight to the concrete column calculator for above-grade columns.
Concrete Volume per Sonotube by Diameter and Depth
This table gives the concrete volume (in cubic feet, no waste) for a single tube at common diameters and depths. Multiply by your tube count, then add 10% waste before ordering.
| Diameter | 3 ft deep | 4 ft deep | 5 ft deep |
|---|---|---|---|
| 8 in | 1.05 cu ft | 1.40 cu ft | 1.75 cu ft |
| 10 in | 1.64 cu ft | 2.18 cu ft | 2.73 cu ft |
| 12 in | 2.36 cu ft | 3.14 cu ft | 3.93 cu ft |
| 16 in | 4.19 cu ft | 5.59 cu ft | 6.98 cu ft |
| 18 in | 5.30 cu ft | 7.07 cu ft | 8.84 cu ft |
Volume scales with the square of the diameter, so jumping from a 12-inch to an 18-inch tube more than doubles the concrete needed at the same depth. That is why oversizing "just to be safe" gets expensive fast on multi-pier projects.
How Many 80-lb Bags per Sonotube
One 80-lb bag of concrete mix yields about 0.60 cubic feet of finished concrete (per Quikrete and Sakrete published yields). Divide the tube volume by 0.60 and round up — you cannot buy a partial bag. The table below already includes roughly 10% waste.
| Diameter | 3 ft deep | 4 ft deep | 5 ft deep |
|---|---|---|---|
| 8 in | 2 bags | 3 bags | 4 bags |
| 10 in | 3 bags | 4 bags | 5 bags |
| 12 in | 5 bags | 6 bags | 8 bags |
| 16 in | 8 bags | 11 bags | 13 bags |
| 18 in | 10 bags | 13 bags | 17 bags |
A 60-lb bag yields about 0.45 cubic feet, so multiply the 80-lb count by roughly 1.33 if you are buying the smaller bags. For a deeper breakdown of bag yields by project, see our how many bags of concrete guide.
Bagged vs. Ready-Mix: The Crossover Point
For a handful of small tubes, bagged mix is simplest. But bag count climbs fast across multiple piers, and mixing 40+ bags by hand is a long, exhausting day.
| Tube Count (12 in × 4 ft) | Total Volume | 80-lb Bags | Practical Choice |
|---|---|---|---|
| 1–2 tubes | 0.13–0.26 cu yd | 6–12 | Bagged |
| 3–6 tubes | 0.39–0.77 cu yd | 18–35 | Bagged (or mixer rental) |
| 7–12 tubes | 0.90–1.55 cu yd | 41–70 | Crossover zone |
| 12+ tubes | 1.55+ cu yd | 70+ | Ready-mix |
The usual crossover is around 1 cubic yard (roughly 45 bags of 80-lb mix). Above that, short-load ready-mix delivery is often cheaper per yard and far less labor, though most suppliers charge a short-load fee under 3–4 yards. Compare the two in our ready-mix vs. bagged guide and the detailed bagged vs. ready-mix cost comparison.
Standard Sonotube Diameters and the Footing at the Base
Sonotube and similar fiber forms are sold in standard diameters: 8, 10, 12, 14, 16, 18, and 24 inches, in lengths up to 12 feet. Buy each tube 6–12 inches longer than the finished height so you can cut it level after setting.
A straight cylinder bears on a small area of soil. For higher loads or weaker soil, the pier needs a wider footing or bell at the base to spread the load. Two common solutions:
- Bigfoot-style bell forms snap onto the bottom of a standard tube to create an integral flared footing (e.g., a 20- or 28-inch base under a 10- or 12-inch column), poured monolithically with the pier.
- A separate spread footing poured first, with the tube set on top — common for heavier deck and structural loads.
Sizing the bearing area is load-dependent. For deck-specific footing sizing, use the concrete deck footing calculator; for standalone pier footings, the concrete pier footing calculator.
Frost Depth, Rebar, and Bracing
Embed below the frost line. Per IRC R403.1.4, exterior footings must extend below the frost line of the locality (or be frost-protected by an approved method). Setting a pier only to the frost line is not enough — the bearing surface must be below it so the soil under the footing never freezes and heaves. Frost depths range from near zero in the Deep South to 48–60+ inches across the northern states; always confirm the figure with your local building department.
Add rebar in structural piers. A single vertical bar (or a small cage of 2–4 bars with ties) controls cracking and ties the pier to its footing. Many decks also use a vertical bar that extends up into a Bigfoot or pier base and bonds to the post anchor. See our when to use rebar guide for sizing.
Brace and level before you pour. Set each tube on a 4–6 inch gravel base for drainage, backfill around it while checking plumb, and stake diagonal lumber braces to the above-grade section. Pour in 12-inch lifts, rodding each lift to release voids, and set anchor bolts or post bases while the concrete is still workable. Our concrete form bracing guide and how to pour concrete guide walk through the full sequence.
Get Your Exact Numbers
Enter your tube diameter, depth, and count in the calculator above to get exact cubic yards, 80-lb bag count, and a ready-mix order with waste included. Planning a deck, pergola, or fence? Pair this with the concrete cost calculator to price the full job before you buy a single tube.