Column & tube calculator
Sizes round column forms and tube footings — deck posts, porch columns, mailbox and sign footings. Round forms hold less than people estimate, so this is the calculation most often done wrong by eye.
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This calculator needs JavaScript. The reference table below covers the common cases.
| Diameter | ft³ | 80 lb bags |
|---|---|---|
| 8 in | 1.40 | 3 |
| 10 in | 2.18 | 4 |
| 12 in | 3.14 | 6 |
| 16 in | 5.59 | 10 |
The formula
π × (diameter ÷ 24)² × height (ft) × quantity ÷ 27 = cubic yards
Worked example
Six 12 in tubes, 4 ft deep: π × 0.5² × 4 = 3.14 ft³ each. × 6 = 18.8 ft³ = 0.70 yd³.
Reference table
| Diameter | ft³ | 80 lb bags |
|---|---|---|
| 8 in | 1.40 | 3 |
| 10 in | 2.18 | 4 |
| 12 in | 3.14 | 6 |
| 16 in | 5.59 | 10 |
Assumptions
- Assumes a true cylinder — no bell or flared base.
- Add a separate footing calculation if the design calls for a belled bottom.
- Required depth is set by local frost depth, which your building department determines.