Concrete Column Calculator
Concrete columns and post bases require a precise volume calculation — under-ordering means a cold joint, over-ordering wastes money. This calculator handles both round columns (like Sonotube forms) and square columns. Enter your dimensions to get cubic yards, with an 80 lb bag count for small pours.
How to use this calculator
- Enter the column diameter in inches — measure the inside of your form tube.
- Enter the height in feet and the number of columns.
- Adjust the waste factor if needed.
- Read your total cubic yards and bag count for all columns combined.
How we calculate this
Round column volume = π × (diameter/2)² × height, converted to cubic yards. A 12-inch diameter Sonotube 4 feet tall is π × (0.5)² × 4 = 3.14 cubic feet = 0.116 cubic yards. Square column volume = side × side × height ÷ 27. We add 10% waste. Most column pours are small — bags are the norm, but for multiple columns a partial ready-mix load may be more efficient.
What this calculator doesn't include
Column sizing (diameter, height, reinforcement) should be specified by a structural engineer for load-bearing applications. This calculator does not account for the form tube cost (Sonotube), rebar or rebar cage, anchor bolts, or excavation for below-grade sections. Always check local frost-depth requirements for the below-grade portion.
Example concrete estimates — Concrete Column
Pre-calculated for common project sizes. Includes 10% waste factor.
| Diameter × Height | Cubic Yards | With Waste | 80 lb Bags |
|---|---|---|---|
| 8" dia × 4 ft tall | 0.052 yd³ | 0.06 yd³ | 3 |
| 8" dia × 8 ft tall | 0.103 yd³ | 0.11 yd³ | 6 |
| 10" dia × 4 ft tall | 0.081 yd³ | 0.09 yd³ | 5 |
| 10" dia × 8 ft tall | 0.162 yd³ | 0.18 yd³ | 9 |
| 12" dia × 4 ft tall | 0.116 yd³ | 0.13 yd³ | 6 |
| 12" dia × 8 ft tall | 0.233 yd³ | 0.26 yd³ | 12 |
| 16" dia × 4 ft tall | 0.207 yd³ | 0.23 yd³ | 11 |
| 16" dia × 8 ft tall | 0.414 yd³ | 0.46 yd³ | 21 |
All estimates include a 10% waste factor. Under 1 yd³ is typically practical with bagged mix; over 1 yd³ usually warrants a ready-mix truck.
Frequently asked questions
For a typical residential deck, 10–12 inch diameter Sonotubes are most common. The footing must extend below the frost line and spread the load adequately. A structural engineer or your local building department can specify the exact diameter based on the load and soil. Most deck columns also need a flared base (bell bottom) for load spreading.
A 12-inch Sonotube 4 feet tall holds 3.14 cubic feet = 0.116 cubic yards. With 10% waste, that is 3.46 cubic feet. You need about 6 bags of 80 lb mix (each yields 0.60 cubic feet). If you have multiple columns, calculate total yards and consider a mini ready-mix load — it is often cheaper than carrying many bags.
For structural columns, yes — rebar is required to handle tensile and bending forces. A typical residential deck post footing uses 2–4 vertical rebar rods with horizontal ties (a rebar cage). For simple fence posts and non-structural applications, plain concrete is acceptable. Always confirm with your local building code.
The below-grade portion must extend below the local frost depth to prevent frost heave. Frost depth ranges from 0 inches in Florida to 60+ inches in Minnesota. Check your local code — the frost depth map from ASCE 7 is a reliable reference. The bottom of the footing should sit on undisturbed or well-compacted soil.
A round column uses less concrete than a square column of the same nominal size. A 12-inch round column has an area of 113 sq in; a 12-inch square column has 144 sq in — about 27% more concrete. Round Sonotube forms are also faster to set up, easier to strip, and produce a cleaner architectural finish.