Concrete Column Calculator
A 12-inch diameter, 8-foot tall concrete column takes 0.23 cubic yards of concrete — about 12 bags of 80-lb mix per column. Enter diameter, height, and quantity below for total volume across multiple columns plus sonotube sizing notes.
Pro Tips
- →Typical column diameters range from 10-24 inches
- →Include rebar reinforcement for structural columns
- →Use sonotubes or forms for round columns
- →Pour columns in one continuous operation
- →Vibrate concrete to remove air pockets
Includes 10% waste factor
Cost Estimate
Estimated material costs for your project
Recommendation: Bagged Concrete
For smaller projects, bagged concrete gives you more control and less waste.
18 bags × 80lb
0.38 cubic yards + delivery
Prices vary by location and time. Contact local suppliers for accurate quotes.
For general step-by-step instructions, read our complete When To Use Rebar and How To Pour Concrete.
What This Calculator Covers
This tool calculates concrete volume for vertical columns, pillars, and piers — both round (cylindrical) and square cross-sections. Use it for porch columns, deck support piers, structural posts, fence pillars, and decorative pillars. The math differs by shape:
- Round column: volume = π × radius² × height
- Square column: volume = side × side × height
A 12-inch diameter round column 8 feet tall takes 0.23 cubic yards (about 12 bags of 80-lb mix) per column. A 12×12-inch square column of the same height takes 0.30 cubic yards — a square section holds about 27% more concrete than a round one of the same nominal width, because the circle is inscribed inside the square.
Round columns are typically formed with a cardboard tube (Sonotube or equivalent); square columns are formed with built plywood or lumber forms. This is a general column tool — if you're sizing strictly to brand tube dimensions, the sonotube calculator handles standard fiber-tube sizes by length.
Round Column Volume by Size
The table below shows volume per round column at 8 feet tall — a common porch and deck-pier height. For other heights, scale linearly (a 4-ft column is half these numbers; a 12-ft column is 1.5×).
| Diameter | Volume per 4 ft (cu yd) | Volume per 8 ft (cu yd) | Volume per 12 ft (cu yd) | 80-lb Bags per 8-ft Column (incl. 10% waste) |
|---|---|---|---|---|
| 8 in | 0.05 | 0.10 | 0.15 | 5 |
| 10 in | 0.08 | 0.16 | 0.24 | 8 |
| 12 in | 0.12 | 0.23 | 0.35 | 12 |
| 16 in | 0.21 | 0.41 | 0.62 | 20 |
Multiply by your column count to get total project volume. Four 12-inch × 8-ft columns = about 0.92 cubic yards (roughly 46 bags), which sits right at the bagged-versus-ready-mix breakpoint.
Square Column Volume by Size
Square columns are formed with built plywood or dimensional-lumber forms rather than a tube. Volume is simply the cross-sectional area times the height. The table below is for 8-foot-tall square columns.
| Cross-Section | Volume per 8 ft (cu yd) | 80-lb Bags per Column (incl. 10% waste) |
|---|---|---|
| 8 × 8 in | 0.13 | 7 |
| 10 × 10 in | 0.21 | 10 |
| 12 × 12 in | 0.30 | 15 |
| 16 × 16 in | 0.53 | 26 |
Bags vs. Ready-Mix for Small Pours
Most residential column projects are small enough to mix from bags, but the labor adds up fast. A standard 80-lb bag of concrete mix yields about 0.6 cubic feet (0.022 cubic yards). The breakpoint for ordering a ready-mix truck instead of bagging is around 1 cubic yard.
| Project | Total Volume (cu yd) | 80-lb Bags | Practical Method |
|---|---|---|---|
| 2 × 12-in round, 8 ft | 0.46 | 23 | Bags |
| 4 × 12-in round, 8 ft | 0.92 | 46 | Bags or short-load |
| 6 × 12-in round, 8 ft | 1.38 | 69 | Ready-mix / short-load |
| 8 × 16-in square, 8 ft | 4.24 | 212 | Ready-mix |
Mixing 46 bags by hand is roughly a full day for two people. Above 1 cubic yard, a short-load ready-mix delivery is usually cheaper once you price your time and a rental mixer. For total delivered cost, run your number through the concrete cost calculator.
Footing at the Base of a Column
A load-bearing column needs a footing beneath it to spread the load into the soil — a column poured directly on grade will settle or punch through. The footing is a wider pad (often a bell or square pad) cast below the frost line.
- Frost depth. In cold climates the footing base must sit below the local frost line (commonly 36–48 inches, but check your jurisdiction) so frost heave can't lift the column.
- Pad size. Footing width is set by the column load and the soil bearing capacity. The 2021 IRC Table R403.1 gives prescriptive footing sizes for typical residential loads; engineered designs follow ACI 318.
- Monolithic vs. separate. A deck pier is often poured monolithically — a wide pad transitioning into the round column above. Size the pad with the concrete footing calculator or the pier footing calculator, and add that volume to the column volume from this page.
Forms, Rebar, and Concrete Strength
Forms. Round columns use cardboard fiber tubes (Sonotube and equivalents) in standard diameters of 8, 10, 12, 14, and 16 inches; square and fluted decorative tubes exist too. Buy tubes 6–12 inches longer than the finished height for leveling and cutting. A 12-inch tube full of fresh concrete carries roughly 50 lbs of lateral pressure per linear foot near the base — brace every tube with 2×4 strongbacks and diagonal kickers so it can't bow or blow out. See the form bracing guide for the bracing layout.
Rebar and ties. Structural columns need vertical bars plus horizontal ties:
| Element | Typical Spec | Purpose |
|---|---|---|
| Vertical bars | 4 × #4 or #5, evenly spaced | Carry axial and bending load |
| Horizontal ties | #3 closed loops, every 12–18 in | Confine verticals, resist shear |
| Clear cover | 1.5 in to form face | Protect steel from corrosion |
Assemble the cage before placing it in the form and keep it centered on chairs. ACI 318 sets minimum vertical reinforcement for structural columns at 1% of the gross cross-section, with ties detailed per the code.
Concrete strength. Use 3,000–4,000 PSI mix for residential columns; 4,000 PSI is the common spec for structural columns and exterior piers exposed to freeze-thaw. See what PSI concrete do I need to match the mix to the job.
Pour technique. Pour each column in one continuous lift to avoid a cold-joint weak point, and vibrate or rod aggressively to consolidate concrete around the cage — voids dramatically cut load capacity.
Structural Note
The sizes, rebar patterns, and PSI values here are typical starting points, not a design. Any column carrying real structural load — a porch beam, a deck girder, an outdoor-kitchen roof, or a building post — must be sized by a licensed structural engineer and built to your local code. Column failure is a life-safety issue. Use this calculator to estimate concrete quantities and order materials; use an engineer to confirm the diameter, reinforcement, and footing for your loads. When in doubt, get the design stamped and the permit pulled before you pour.