Pick round, square, or rectangular. Enter size and height. Get concrete volume, rebar cage, bags or ready-mix, and code compliance.
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How this calculator works
Concrete columns are calculated in three parts: the form volume (the empty tube or form you build), the concrete volume (form volume minus the rebar cage), and the rebar cage (vertical bars plus horizontal ties or spiral).1 Most DIY calculators only give you form volume — which slightly over-orders concrete but is fine for planning — and skip rebar entirely, which is where the actual labor and cost hide.
Round: Volume = π × (Diameter ÷ 2)² × Height Square: Volume = Side × Side × Height Rectangular: Volume = Width × Length × Height Vertical rebar = Bars × (Above + Below + Lap) Horizontal ties = ⌈Height ÷ Tie spacing⌉ × Tie length per tie
The above + below split matters. A column sitting on a footing has two height zones: above-grade (the visible column) and below-grade (embedment into the footing or pier). Both need concrete, but the below-grade volume is often missed when the calculator only asks for "height." The result is a 30–40% shortfall on a standard deck pier.
Round, square, and rectangular columns all use the same volume math. The rebar cage is what makes them structural — and it is the part most DIY calculators ignore.
Above-grade vs below-grade — the split that matters
A column sitting on a footing has two zones. The above-grade zone is the visible column that carries the load to the beam above. The below-grade zone is the embedment into the footing — typically 24–36 inches for a deck pier, more in frost climates. Both zones need concrete, and both count toward total volume. Calculators that only ask for "column height" under-order by the entire below-grade section.
Column application
Above-grade
Below-grade
Why
Deck pier (deck at 3 ft)
36″
36–48″
Below frost line
Porch column (8 ft ceiling)
96″
24–36″
Sits on footing
Post-frame barn column
144″
48–60″
Deep embedment for lateral load
Fence post (chain link)
60–72″
24–36″
Frost + uplift resistance
Structural basement column
Basement height
0″
Bears on footing, no embedment
Field note from the estimating desk: the most expensive mistake on a column pour is setting the rebar cage wrong. The cage has to be centered in the form, with 1.5–3 inches of clear cover to the outside face. If the vertical bars are pushed against the form, the column has zero cover on that side and will rust through in 10–15 years — before the concrete itself fails. Build the cage on a template at the correct diameter, lower it in, and check the clear cover with a tape before pouring. Second mistake: skipping the below-grade section. A 12"×96" Sonotube with 36" of embedment is 132" of concrete, not 96" — a 27% difference that lands as a shortfall halfway through the pour.
Sonotube sizes and standard applications
Diameter
Typical use
Max above-grade height
Concrete per LF
8″
Fence posts, mailbox posts, light bollards
6 ft
0.35 ft³
10″
Deck piers (light), small pergolas
8 ft
0.55 ft³
12″
Deck piers (standard), porch columns
10 ft
0.79 ft³
14″
Heavy deck piers, small carports
12 ft
1.07 ft³
16″
Structural piers, small pole barns
12 ft
1.40 ft³
18″
Large structural piers, pole barns
14 ft
1.77 ft³
20″
Heavy structural piers, highway signs
14 ft
2.18 ft³
24″
Bridge piers, very heavy loads
16 ft
3.14 ft³
Rebar cage sizing by column diameter
Standard rebar cages for concrete columns follow a minimum-4-bar rule, with additional bars added as the column gets larger. The table below reflects typical residential and light commercial practice.3
Column diameter / side
Minimum bars
Bar size
Typical tie spacing
8″
4
#3 or #4
12″ OC
10″
4
#4
12″ OC
12″
6
#4
12″ OC
14–16″
6
#4 or #5
12″ OC
18–24″
8
#4 or #5
9–12″ OC
24″+ (structural)
8+
#5 or #6
6–9″ OC
Frequently asked questions
How much concrete do I need for a column?
For a round Sonotube: π × (diameter ÷ 2)² × total height. A 12″ column with 96″ above grade and 36″ below grade is 132″ tall, which is 8.64 cubic feet or 0.32 cubic yards. For square or rectangular columns, use side × side (or width × length) × height. Always include below-grade embedment in the total height.
How deep should a column pier be?
Below-grade embedment for a concrete pier is below the frost line — typically 24–36 inches in the South and 36–48 inches in the North. For a deck pier carrying a structural load, the embedment plus footing pad must go below frost. For a fence post, minimum 24–36 inches. For a structural pole barn column, 48–60 inches is common.
How many rebar bars do I need in a column?
Minimum 4 vertical bars for any concrete column, per ACI 318.3 Add bars as the column gets larger: 6 bars at 12–16 inch diameter, 8 bars at 18–24 inch. Standard bar size is #4 (1/2 inch) for residential columns; #5 or #6 for heavy structural work.
How many ties do I need in a column?
Ties are horizontal rings around the vertical bars, spaced at 6–18 inches on center. The number is ⌈column height ÷ tie spacing⌉. For a 132 inch column with 12 inch ties, that is 11 ties. Each tie length is the cage perimeter (plus hook length ~6 inch), not the column perimeter — the ties wrap the rebar cage, not the form.
Bags or ready-mix for columns?
Columns are almost always bags territory. A single 12 inch Sonotube 8 ft tall is 0.20 cubic yards — about 27 bags of 60 lb. Even 8 columns is only 1.6 yards, right at the ready-mix break-even. For fewer than 4 columns, bags are almost always cheaper. For a pole barn with 20+ deep-set columns, ready-mix usually wins. The calculator shows both.
Should the rebar cage touch the form?
No. The rebar cage must sit inside the form with minimum 1.5 inches of clear cover to the form face for cast-in-place columns (3 inches if soil-exposed below grade).4 If the bars touch the form, the column has no cover on that side, water reaches the steel, and rust splits the column from inside. Build a template at the correct cage diameter and lower it in.
How do I pour a Sonotube column?
Set the tube plumb on the footing, brace it in 2–3 directions, lower the rebar cage into the tube (centered), and pour in 2-foot lifts. Consolidate each lift with a piece of rebar or a small vibrator to eliminate voids. Leave the tube in place for aesthetic form — it is permanent, not a form to remove. Cut the top flush after 24 hours.
Can I pour a column in one pour from base to top?
Yes, if the pour is under 6 feet tall. Above 6 feet, form pressure can burst the tube, especially with a rapid pour. Pour in lifts of 2–3 feet and consolidate between lifts. Above 10 feet, consider a pump truck or a longer pour time with continuous consolidation.
What is the difference between a pier and a column?
A pier is a short, often below-grade or partially-buried structural element, usually round (Sonotube), that transfers load from a beam or post to the footing. A column is a taller above-grade structural element that carries load from above. In practice, "concrete pier" and "concrete column" often refer to the same thing — the difference is height and whether the base is visible.
Do I need a footing for a concrete column?
Yes for any structural column. A column transfers load to a footing, which spreads it across the soil. Columns without a footing (directly on grade) will sink and crack the structure above. For fences and non-structural piers, a wider base of the Sonotube at the bottom — called a "bell" — can substitute for a footing, but the belled base must be at least 2× the column diameter.
Standards and sources
Portland Cement Association — Concrete Columns and Piers: Design and Construction. Volume formulas, form requirements, and consolidation guidance for cast-in-place columns. cement.org
International Code Council — IRC R403.1 Foundations and Footings. Footing and pier requirements for residential construction. codes.iccsafe.org
American Concrete Institute — ACI 318 Building Code for Structural Concrete. Minimum 4-bar rule, bar size limits, and tie requirements for columns. concrete.org
Concrete Reinforcing Steel Institute — Clear Cover Requirements for Cast-in-Place Concrete. 1.5 inch minimum for columns, 3 inch for soil-exposed surfaces. crsi.org
American Concrete Institute — ACI 308 Guide to Curing Concrete. Curing time and strength gain for column concrete. concrete.org
Sonotube — Concrete Forms Technical Guide. Standard tube diameters, maximum above-grade heights, and pour rate limits. sonotube.com
BM
Builders Measures estimating team
Reviewed against ACI 318 column requirements and Sonotube technical guidance. Column sizing and rebar details in this calculator reflect standard residential and light commercial practice — always confirm structural column design with a licensed engineer for anything beyond a single-story residential load. Last reviewed October 2026.
Estimates only. Confirm column sizing, rebar, and footing requirements with a structural engineer or your local building department before pouring. Last reviewed October 2026.