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Column Concrete Calculator
Concrete for round columns, piers and posts. Enter diameter, height and quantity: get cubic yards and bags instantly.
Estimates only. Bag yields per manufacturer specs (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³). Ready-mix trucks carry ≈ 10 yd³. Always round up and confirm with your supplier.
Deck piers, fence posts set in concrete and round columns all use the cylinder formula. The free column concrete calculator below handles one pier or a whole row: enter diameter, height and how many you need.
How to use the column concrete calculator
- Measure the hole or tube diameter in inches.
- Enter the depth or height in feet.
- Enter how many identical columns or piers you are pouring.
- The calculator totals the volume across all of them, with waste and bag counts.
Formula
Volume = π × radius² × height. Multiply by the number of columns, then divide by 27 for cubic yards.
Practical tips
- A 12 in diameter pier, 4 ft deep needs 3.1 cubic feet, about 6 bags of 80 lb mix.
- Sonotubes keep round piers neat and make volume predictable.
- Bell out the bottom of post holes in soft soil for extra bearing.
- Set a waste margin of 10 percent: holes are rarely perfect cylinders.
Frequently asked questions
How many bags per concrete pier?
A 12 in by 4 ft pier needs 6 bags of 80 lb concrete. An 8 in by 3 ft pier needs about 2 bags.
How deep should deck piers be?
Below the frost line, typically 36 to 48 inches, depending on your climate zone.
Tube or dug hole: which is better?
Tubes give exact volume and smooth sides. Dug holes are cheaper but use more concrete.
More tools: the concrete calculator hub and the post hole calculator.
Worked examples
Example 1: 12 in diameter, 8 ft high. Volume = 0.23 cubic yards. With 10% waste: 0.26 cubic yards (12 x 80 lb bags).
Example 2: 16 in diameter, 8 ft high. Volume = 0.41 cubic yards. With 10% waste: 0.45 cubic yards (21 x 80 lb bags).
Column concrete reference table
Cubic yards before waste; 80 lb bags include 10% waste.
| Column | Cubic yards | 80 lb bags |
|---|---|---|
| 8 in dia x 4 ft | 0.05 | 3 |
| 12 in dia x 4 ft | 0.12 | 6 |
| 12 in dia x 8 ft | 0.23 | 12 |
| 16 in dia x 8 ft | 0.41 | 21 |
More column questions
How many bags for a 12 inch concrete column?
A 12 in diameter column 8 ft high needs 12 x 80 lb bags with 10% waste.
Do concrete columns need rebar?
Yes, structural columns need vertical rebar with ties. This calculator estimates concrete volume only.