Concrete Column Calculator
Find the concrete volume needed for round or rectangular columns and posts.
📖 What is a Concrete Column Calculator?
A concrete column calculator finds the volume of concrete needed to pour a round or rectangular column, then converts it into cubic yards for ready-mix ordering and into premixed bag counts. Columns show up throughout residential and light commercial construction: porch and deck support posts, carport columns, structural piers, and decorative or load-bearing pillars.
Round columns are calculated as cylinders: volume equals pi times the radius squared times the height. Rectangular or square columns are simple rectangular prisms: width times depth times height. Because columns are almost always poured in matching sets (four porch posts, six deck supports), the calculator includes a quantity field so you size the whole set in one pass instead of multiplying by hand.
A common source of ordering error is entering the diameter where the formula needs a radius, or forgetting to convert inches to feet before multiplying by a height given in feet. This calculator takes the diameter (or width and depth) directly in inches and the height in feet, matching how these dimensions are usually specified on site and on drawings, and does the unit conversion internally.
This tool is closely related to the Concrete Estimator - Tube, which uses the same cylinder math but is framed specifically around Sonotube-style cardboard forms for round footings and piers. Use whichever framing matches your project; the underlying formula is identical for the round mode here.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Four 12 inch round porch columns
Example 2 - One 16 inch round pier
Example 3 - Six 12x12 inch square posts
❓ Frequently Asked Questions
🔗 Related Calculators
How do I calculate concrete for a round column?
Use Volume = pi x radius squared x height, where the radius is half the diameter. A 12 inch diameter column 8 feet tall has a radius of 0.5 feet, so the volume is pi x 0.5 squared x 8 = 6.28 cubic feet per column.
How do I calculate concrete for a square or rectangular column?
Multiply width times depth times height, all in feet. A 12 by 12 inch (1 by 1 foot) column that is 9 feet tall needs 1 x 1 x 9 = 9 cubic feet of concrete.
How much concrete does one deck or porch column need?
A typical 12 inch diameter, 8 foot tall round column needs about 6.28 cubic feet, or roughly 0.23 cubic yards, of concrete. Four such columns need about 25 cubic feet, or just under 1 cubic yard.
What is the difference between this calculator and the Concrete Estimator - Tube?
Both use the same cylinder formula. This calculator is aimed at finished architectural or structural columns, round or rectangular, sized by diameter or width/depth and height. The Concrete Estimator - Tube is specifically for Sonotube-style cardboard forms used for round footings and piers, typically shorter and wider relative to their diameter.
Should I subtract the volume of rebar inside a column?
For estimating purposes, no. Reinforcing steel occupies a small fraction of a column's cross-sectional area, typically under 2 percent, which is well within the standard waste allowance already built into most concrete orders.
How many bags of concrete do I need for a fence post or column?
Divide the column's volume in cubic feet by the bag yield: about 0.45 cubic feet for a 60 lb bag or 0.6 cubic feet for an 80 lb bag. A single 12 inch diameter, 8 foot column (6.28 cubic feet) needs about 14 bags of 60 lb concrete.
What is a typical column diameter for a residential porch?
Decorative or load-bearing porch columns are commonly 8 to 12 inches in diameter for the concrete core, sometimes clad in a larger decorative sleeve. Structural sizing should always follow the load calculations from a structural engineer or local building code.
How tall should a concrete column be before I need extra reinforcement?
There is no universal height cutoff; slenderness (the ratio of unsupported height to the smallest cross-sectional dimension) governs whether a column needs additional reinforcement or a larger cross-section to resist buckling. Consult a structural engineer for load-bearing columns, especially tall or slender ones.
Can I calculate an octagonal or non-round, non-rectangular column?
Not directly with this tool. Approximate an octagonal column as a circle using its across-flats diameter for a close estimate, or calculate the polygon's cross-sectional area separately and use the Concrete Calculator's Direct Volume mode with area times height.
How much does it cost to pour a concrete column?
Materials cost is the column's cubic yard volume multiplied by your local ready-mix price (commonly $120 to $180 per cubic yard) or bag count multiplied by bag price, plus separate costs for formwork, rebar, and labor which this calculator does not include.