Concrete Column Calculator
Enter the diameter or side and the height, and this concrete column calculator returns the volume for round and square columns in cubic yards and cubic meters, plus bag counts and a cost estimate. It handles porch piers, deck footings in tube forms, structural pillars and cardboard sonotubes.
Concrete Column Calculator
Most people reach this page for a round pour. A sonotube is the fiber tube form that shapes a smooth cylinder for a deck pier or porch post, so the words sonotube, pier and column describe the same math. The volume is a cylinder; get the radius right and the rest follows.
How to calculate concrete for a column
For a round column, volume equals pi times the radius squared times the height. Radius is half the diameter. When the diameter is in inches and the height is in feet, a quick form is: volume in cubic feet equals pi times the square of the diameter divided by 24, times the height in feet. For a square column, volume equals width times depth times height.
Multiply a single column by the number of identical columns to get the project total. Add 5 to 10 percent for waste, since some mix sticks to the form and the base.
Worked example, four porch piers
Say a porch sits on four round piers, each 12 inches across and 8 feet tall. Convert the diameter to a radius in feet: 12 divided by 24 is 0.5 feet. One pier is pi times 0.5 squared times 8, which is 3.14 times 0.25 times 8, or 6.28 cubic feet. Four piers come to 25.1 cubic feet. Add 10 percent for waste to reach 27.6 cubic feet, which is 1.02 cubic yards, or about 46 bags of 80 pound mix. At just over one yard, this is the point where a ready mix delivery starts to compete with mixing bags.
Common column sizes at a glance
Column volume scales with height, so the table lists cubic feet per foot of height and the 80 pound bag count per foot. Multiply by the height, then by the number of columns.
| Column | Per foot of height (cu ft) | 80 lb bags per foot |
|---|---|---|
| 9 in square | 0.56 | about 1 |
| 12 in square | 1.00 | about 1.7 |
| 16 in square | 1.78 | about 3 |
| 10 in round | 0.55 | about 0.9 |
| 12 in round | 0.79 | about 1.3 |
| 16 in round | 1.40 | about 2.3 |
| 18 in round | 1.77 | about 3 |
Sonotube tips that affect your order
- Cut the tube about 2 inches above finished grade so you can trim after the pour.
- Set the tube on a footing or compacted base at least twice the tube diameter, so a 12 inch tube sits on a 24 inch footing.
- Brace at two heights with lumber staked to the ground, and check plumb before, during and after the pour.
- Seal the base with soil or foam so the mix does not leak out the bottom.
- Overfill by about an inch, then screed flat, because concrete settles as air escapes during vibration.
Reinforcement for structural columns
Structural columns need steel to resist bending and buckling. A common residential pattern is four vertical No. 4 bars for columns 12 inches and larger, with No. 3 ties wrapped every 12 to 18 inches. Keep at least 1.5 inches of cover between the steel and the form face, and extend the vertical bars into the footing below so the column and footing act together. Bar size, tie spacing and cover for any load bearing column must follow the structural drawings and ACI 318. Reinforcement does not change the concrete volume, so budget the steel on its own.
Why column pours come up short
- Entering a radius where the tool asks for diameter. The formula squares the radius, so a full diameter typed into a radius field changes the result four times over.
- Multiplying columns of different sizes together. The quantity field assumes identical columns, so run each size separately and add the totals.
- Leaving waste at zero across many piers. A small shortfall per pier adds up to a real gap on pour day.
- Forgetting the footing or a belled base. The plain cylinder stops at the joints; add the footing with the footing calculator.
Related calculators
- Footing calculator for the pad or pier footing under a column
- Slab calculator for a porch or floor slab between columns
- Bags calculator to turn column volume into a bag count
- How to calculate concrete guide for formulas and examples
Frequently asked questions
How much concrete do I need for a round column?
Use pi times the radius squared times the height. A 12 inch column 8 feet tall needs about 6.28 cubic feet, or roughly 11 bags of 80 pound mix. Add 10 percent for waste.
What size sonotube do I need for a porch column?
Residential porch columns commonly use 10 or 12 inch tubes. Columns carrying a second story or heavy roof loads step up to 14 or 16 inches. Your engineer or local code sets the minimum based on the load.
How many bags of concrete fill a 12 inch sonotube?
A 12 inch tube holds about 0.79 cubic feet per foot of height, so a 4 foot tube needs about 3.14 cubic feet, or roughly 6 bags of 80 pound mix.
Do concrete columns need rebar?
Structural columns do. A common pattern is four vertical No. 4 bars with No. 3 ties, extended into the footing. Short decorative piers may use a single centered bar. Follow the structural drawings.
Should I use bags or ready mix for columns?
For one to three small columns, bags are practical. For four or more full height columns, or anything over 16 inches across, ready mix is more efficient. The crossover is near one cubic yard.
Can I use this for a square column?
Yes. Switch to square mode and enter width, depth and height. The tool uses width times depth times height instead of the cylinder formula.
References
- American Concrete Institute, ACI 318 Building Code Requirements for Structural Concrete: https://www.concrete.org
- Quikrete, Concrete Mix 1101 data sheet (bag yields): https://www.quikrete.com/PDFs/DATA_SHEET-Concrete Mix 1101.pdf
- Portland Cement Association, concrete technology library: https://cement.org
- ASTM C94, Standard Specification for Ready Mixed Concrete: https://www.astm.org/c0094_c0094m-22.html
Methodology: round volume uses pi times radius squared times height; square volume uses width times depth times height, converted to a common unit and divided by 27 for cubic yards. Bag counts use published manufacturer yields. Estimates are for planning; confirm column size, reinforcement and cover with a licensed engineer. Recommended: attribute this page to a named author and add a review date.