Concrete Column Calculator
Find the concrete volume for a round or square column, from its size and height.
Reviewed by the ToolNestr Editorial Team — July 2026
How the concrete column calculator works
A concrete column's volume depends on its cross-section shape and its height. A round column is a cylinder, so its volume is π times the radius squared times the height. A square column is a rectangular prism, so its volume is simply side times side times height. Because a circle inscribed in a square only fills about 78.5% of the square's area, a round column always uses noticeably less concrete than a square one of the same width — about 27% less, in fact.
Working in mixed units is common on the job site — diameter or side length in inches, height in feet — so the calculator converts the cross-section dimension to feet before multiplying, keeping everything in cubic feet before converting to cubic yards for ordering ready-mix, or to bag counts for smaller pours. A standard 80-pound bag of concrete mix yields about 0.6 cubic feet once mixed, and a 60-pound bag about 0.45 cubic feet.
This tool estimates concrete volume only. Most structural columns — anything supporting a roof, deck, or floor above — need vertical rebar and horizontal ties sized per ACI 318 to resist bending, buckling, and the loads coming down through them. Reinforcement, footing size, and column spacing should be verified against your local building code and, for anything load-bearing, a licensed engineer.
Pick the shape
Round or square cross-section.
Enter size & height
Diameter or side in inches, height in feet.
Order concrete
Cubic yards for ready-mix, or bags for a small pour.
The formula explained
Round column
= π × (dia⁄24)² × height. A 12 in dia, 8 ft column: π × 0.5² × 8 = 6.28 ft³.
Square column
= (side⁄12)² × height. A 12 in side, 8 ft column: 1² × 8 = 8 ft³.
Cubic yards & bags
yd³ = ft³ ÷ 27; 80 lb bags = ft³ ÷ 0.6.
Worked example
Four round 16 in diameter porch columns, each 9 ft tall.
Where concrete columns are used
Porch and portico supports
Round columns carrying a roof overhang are a common exterior use, often finished with a decorative form liner or wrapped in a fiberglass sleeve.
Structural building piers
Square or round columns carrying beam and floor loads in a framed building, sized by an engineer to the actual load path.
Bridge and dock pilings
Round columns are common for piers exposed to water or soil pressure from all sides, since a circular shape resists lateral loads evenly.
Deck and railing posts
Small-diameter columns set below a deck post give a durable, rot-proof base that outlasts a wood post buried directly in soil.
Real-world context
A covered porch with four round support columns shows a common multi-column job: four 18-inch diameter columns, each 10 ft tall, need π × 0.75² × 10 ≈ 17.67 cubic feet per column, about 70.7 cubic feet total — roughly 2.62 cubic yards, typically ordered as a single ready-mix delivery rather than poured column by column with bags.
A large square structural pier for a heavy beam shows why shape matters: a 24-inch square column 12 ft tall needs 2² × 12 = 48 cubic feet — noticeably more than an equivalent round column of the same width would need, since a square column fills its entire bounding box while a circle only fills about 78.5% of it.
A small deck railing post base shows the other end of the scale: an 8-inch diameter column just 3 ft tall needs only about 1.05 cubic feet, comfortably covered by two 80 lb bags — a case where mixing by hand at the job site makes far more sense than ordering ready-mix for a single small pour.
Multiplying a single-column figure by the count of identical columns, as the porch example does, is the fastest way to order material for a repeated pattern — but it's worth double-checking that every column really is identical before relying on that shortcut, since even a small height difference between columns on a sloped site changes the total meaningfully.
Common misconceptions
"A round and square column of the 'same size' use about the same concrete." Not true. If "same size" means the same width, a circle inscribed in a square only covers about 78.5% of that square's area — the square column uses roughly 27% more concrete than the round one for an identical width and height.
"Concrete volume is the only thing that matters for a column — rebar is a separate line item to add later." It's separate, but not independent. Rebar placement and cover requirements affect the minimum practical column dimensions and how the concrete needs to flow around the cage during the pour — sizing the column without considering the reinforcement it needs to hold can lead to a design that doesn't actually fit together.
Related calculators
Frequently asked questions
How do I calculate concrete for a round column?
Volume = π × radius² × height. A 12-inch (1 ft) diameter column, 8 feet tall: π × 0.5² × 8 = 6.28 cubic feet, which is about 0.23 cubic yards.
How do I calculate concrete for a square column?
Volume = side × side × height, all in the same units. A 12 in (1 ft) square column, 8 ft tall: 1 × 1 × 8 = 8 cubic feet, more than a round column of the same width because a square fills its bounding box completely.
How many bags of concrete does a column need?
An 80 lb bag yields about 0.6 cubic feet of concrete, and a 60 lb bag about 0.45 cubic feet. Divide the column's cubic feet by the bag yield to estimate the bag count, then round up.
Do I need rebar in a concrete column?
Most structural columns need vertical rebar and ties per ACI 318 to resist bending and buckling, especially for anything supporting a roof, deck, or upper floor. This calculator estimates concrete volume only — reinforcement design should follow the applicable code and a qualified professional.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.