Sonotube Calculator
Round piers are cylinders, and cylinder math is easy to fumble. Enter diameter, height and pier count — this sonotube calculator does the π and returns yards, bags and cost.
Concrete needed
0.47 yd³
12.6 ft³
Estimated cost
$77
at $165 per yd³
Approx. weight
1,671 lb
≈ 0.8 tons
Bagged mix
21
80-lb bags
28
60-lb bags
42
40-lb bags
Before you order: add about 10% for uneven subgrade and spillage — that's 0.51 yd³ or 24 × 80-lb bags.
Formula
Each pier is a cylinder — area × height, times the pier count:
volume (ft³) = count × π × [diameter (in) ÷ 24]² × height (ft) cubic yards = volume (ft³) ÷ 27
Handy pier volumes: a 12 in. × 4 ft tube is 3.14 ft³ (0.12 yd³); a 16 in. × 4 ft tube is 5.59 ft³ (0.21 yd³).
Example
- A deck with 4 piers, each a 12 in. tube, 4 ft tall: radius = 0.5 ft.
- One pier: π × 0.5² × 4 = 3.14 ft³; all four: 12.57 ft³.
- Cubic yards: 12.57 ÷ 27 = 0.47 yd³ — with the 10% allowance, about 0.5 yd³.
- Bags: 12.57 ÷ 0.60 = 21 → 21 × 80-lb bags (24 with waste) — no truck needed.
Frequently Asked Questions
How much concrete does a 12-inch sonotube hold?
Per 4 feet of height: 3.14 ft³, or 0.12 cubic yards — six 80-lb bags. The calculator multiplies that by your pier count and adds the 10% ordering allowance.
What diameter sonotube should I use?
Decks commonly use 10–12 in. tubes for average soil and 16 in. where loads spread or soil is soft; follow your deck plan or local code. The diameter must match the tube you buy — the volume scales with the square of it.
How deep should sonotube piers go?
Below the frost line for anything frost-sensitive — 36–48 in. in much of the US — with the tube topped by an above-grade form. Bell the base or pour a footing pad where codes require it.
Do the tubes stay on or come off?
Above grade, peel or cut the fiber tube off once the concrete has cured (or leave a tube rated for burial below grade). Buried fiber that stays wet can hold moisture against the column post.