Concrete Column Calculator
Concrete volume, bags and ready-mix order for round (Sonotube) or square columns. Single column or multiple identical columns at once.
Calculation results
Concrete order amount
—
yd³
Volume per column
—
ft³
Total volume (raw)
—
ft³
Bags needed
—
bags
Estimated cost
$
—
For total orders below 1 yd³, ready-mix carries a short-load fee (~$150). Above 1.5 yd³, ready-mix is dramatically cheaper than bagged per cubic yard.
Informational only. For structural columns (load-bearing posts on multi-storey or commercial work) the design — concrete strength (PSI), rebar size, and tie spacing — must be specified by a licensed engineer following ACI 318.
Column volume formulas
round: V = π × (D / 2)² × H × qty
square: V = side² × H × qty
For round columns enter the inside diameter of the form (Sonotube nominal sizes are accurate to the inside). For square columns use the actual cross-section dimension. Height is centre of footing to top of column.
Worked example — 6 round columns, 12″ Ø × 8 ft, 10 % waste
- Per column = π × (12/2/12)² × 8 = π × 0.25 × 8 = 6.283 ft³
- Total raw = 6 × 6.283 = 37.70 ft³ = 1.396 yd³
- With 10 % waste = 1.54 yd³
- 80 lb bags (0.60 ft³): ⌈41.47 / 0.60⌉ = 70 bags — at this volume, ready-mix is cheaper
Standard Sonotube sizes
| Diameter | ft³ per ft height | yd³ per 8 ft column | 80 lb bags per 8 ft |
|---|---|---|---|
| 6″ | 0.196 | 0.058 | 3 |
| 8″ | 0.349 | 0.103 | 5 |
| 10″ | 0.545 | 0.162 | 8 |
| 12″ | 0.785 | 0.233 | 11 |
| 14″ | 1.069 | 0.317 | 15 |
| 16″ | 1.396 | 0.414 | 19 |
| 18″ | 1.767 | 0.524 | 24 |
| 24″ | 3.142 | 0.931 | 42 |
| 30″ | 4.909 | 1.455 | 66 |
| 36″ | 7.069 | 2.095 | 95 |
Values are per single column at the listed height; values shown without waste factor.
Frequently asked questions
How much concrete for a 12 inch Sonotube?
A 12″ diameter Sonotube at 8 ft height needs about 6.28 ft³ = 0.23 yd³ of concrete per column. For a typical deck with 4-6 piers, total is 1.0-1.5 yd³ — at this size bagged works (about 11 × 80-lb bags per pier) or one short-load ready-mix delivery.
How many bags of concrete per Sonotube?
For 80 lb bags (0.60 ft³ yield), per foot of 12″ Sonotube column: 0.785 / 0.60 = 1.3 bags. So an 8 ft tall 12″ Sonotube ≈ 11 bags. Larger diameters scale with diameter squared (a 24″ at same height = 42 bags).
How deep should a Sonotube footing go?
Below the local frost line. In northern U.S. states: 42-48 inches. In southern states: 12-18 inches. Local code is the authority — check before excavating. The Sonotube extends from the bell footing at depth up to grade.
Should I use a bell-shaped footing or straight Sonotube?
For high loads or soft soil, a bell-shaped footing (wider at the base) distributes load over more area. For typical deck and porch piers in firm soil, a straight Sonotube footing equal to or 1-2″ wider than the post diameter is sufficient.
Square vs round columns — which is better structurally?
Round columns are more efficient for axial loads only (concrete in compression, no shear). Square columns are stronger for combined bending and axial loads, easier to tie reinforcement, and cheaper to form (plywood vs Sonotube). For decorative purposes, both work.
Do I need rebar in a concrete column?
For most residential deck piers under 4 ft tall and 12″ diameter, vertical rebar is recommended but not always required by code (check local). For taller or load-bearing columns: 4 × #4 vertical bars with #3 ties at 12″ spacing is typical for 12″ diameter columns. ACI 318 governs.