Concrete Column Calculator
Calculate concrete for round columns, piers and Sonotube forms from diameter and height. Get cubic yards, cubic feet per column and how many bags to buy.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Concrete needed
- 0.36 cu yd
- 9.6 cu ft for 4 columns including 10% waste
- Per column
- 2.18 cu ft
- 10 in diameter x 4 ft tall, no waste
- 80 lb bags to buy
- 16 bags
- About 4 bags per column
- Approximate weight
- 0.65 tons
- 327 lb per column at 150 lb per cubic foot
Concrete Column formula
Cubic feet per column = 3.1416 x (Diameter (in) / 24)² x Height (ft)
Total cubic feet = Per column x number of columns x (1 + waste %)
Cubic yards = Total cubic feet / 27
Bags = Total cubic feet / bag yield (80 lb = 0.60 cu ft, 60 lb = 0.45 cu ft)Worked example
Six 12 in tube forms 3.5 ft tall for a deck: 3.1416 x (12 / 24)² x 3.5 = 2.75 cubic feet per column. 2.75 x 6 = 16.5 cubic feet. Add 10% waste for 18.1 cubic feet, which is 0.67 cubic yards.
In bags: 18.1 / 0.60 = 31 bags of 80 lb mix, or about 5 bags per column. At 150 lb per cubic foot each column weighs about 410 lb.
Quick reference
| Diameter | Cu ft per ft of height | 3 ft tall | 4 ft tall | 5 ft tall |
|---|---|---|---|---|
| 8 in | 0.35 | 2 | 3 | 3 |
| 10 in | 0.55 | 3 | 4 | 5 |
| 12 in | 0.79 | 4 | 6 | 7 |
How to calculate concrete for a round column
A column is a cylinder, so its volume is pi times the radius squared times the height. Work in feet: divide the diameter in inches by 24 to get the radius in feet, square it, multiply by 3.1416 and by the height. A 10 inch column 4 feet tall is 3.1416 x 0.417² x 4 = 2.18 cubic feet, so four of them need 8.7 cubic feet or 0.32 cubic yards.
Cardboard tube forms are sold in even diameters from 6 to 48 inches and standard 12 foot lengths that you cut to size. Measure the full height of the form, including the portion in the hole, not just what shows above grade.
Bags, mixing and placement
Bagged concrete is the usual choice for columns because each one holds only a few cubic feet. An 80 lb bag yields 0.60 cubic feet, so a 12 inch pier 4 feet tall takes about 5.2 bags, which means buying 6. Add 10 percent for spillage, and buy a bag or two extra: a form that ends up short is hard to top off cleanly later.
Pour in lifts of 12 to 18 inches and rod or vibrate each lift to remove air pockets, especially in narrow tubes. Set anchor bolts or post bases while the concrete is wet. Deck piers must extend below the frost line and normally sit on a wider footing pad, which you can size with the footing calculator.
Key facts
- A 12 in diameter column uses 0.785 cubic feet of concrete per foot of height, or about 1.3 bags of 80 lb mix.
- An 8 in tube uses 0.35 cubic feet per foot, a 10 in tube 0.55, and a 16 in tube 1.40.
- Doubling the diameter of a column quadruples the concrete: a 16 in pier holds four times as much as an 8 in pier.
- Deck piers are usually 8 to 12 in in diameter and extend below the local frost line.
- A 12 in column 4 ft tall weighs about 470 lb at the standard density of 150 lb per cubic foot.
Frequently asked questions
How many bags of concrete for a 12 inch Sonotube 4 feet tall?
About 3.14 cubic feet, which is 6 bags of 80 lb mix or 7 bags of 60 lb mix, before waste.
How many bags of concrete for an 8 inch Sonotube?
An 8 in tube uses 0.35 cubic feet per foot of height. A 4 ft tube needs 1.4 cubic feet, or 3 bags of 80 lb mix.
How much concrete is in a 10 inch column?
0.545 cubic feet per foot of height. A 4 ft column is 2.18 cubic feet, and a 5 ft column is 2.73 cubic feet, roughly 4 to 5 bags of 80 lb mix.
How deep should deck footings be?
Below the frost line, which your local building department sets. Where there is no frost, at least 12 inches below undisturbed grade.
Sources and references
Next steps for this project
The usual order for a concrete & masonry project. See all concrete & masonry calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.