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Concrete Column Calculator

Ready to calculate
Round + Square.
Instant Estimate.
13 Sonotube Sizes.
100% Free.
Privacy Secure.

How it Works

01Pick Shape

Round (sonotube) or square column — pick your form type.

02Dimensions

Diameter or width × breadth, plus height in feet.

03Count & Bag

How many columns + premix bag size (40/60/80/90 lb).

04Bags vs Mix

Bag total vs ready-mix delivered cost comparison.

What is a Concrete Column Calculator?

The Concrete Column Calculator figures out exactly how much concrete you need for round (sonotube) or square columns — perfect for deck piers, porch columns, fence posts, mailbox posts, and foundation piles.

Doubles as a sonotube concrete calculator, fence post concrete calculator, and post hole concrete calculator. Supports all 13 standard sonotube diameters (4, 6, 8, 10, 12, 14, 16, 18, 20, 24, 30, 36, 48 inches) and any custom square dimension.

Converts to premix bag counts (40, 60, 80, or 90 lb) and compares bagged vs ready-mix delivered cost. Includes a 10% waste factor. 100% free, instant, in-browser.

How the Concrete Column Calculator Works

Step 1 — Pick Shape: Round (sonotube) or Square form.
Step 2 — Enter Dimensions: Round — pick diameter from 4 to 48 in. Square — enter width × breadth in inches. Plus height in feet.
Step 3 — Column Count: How many identical columns you're pouring.
Step 4 — Premix Bag Size: 40, 60, 80, or 90 lb — each has different yield per bag.
Step 5 — See Estimate: Volume per column and total, ft³/yd³, bag count, and bag vs ready-mix cost comparison.

The Concrete Column Formulas

ROUND (SONOTUBE):
Volume per column (ft³) = π × (diameter/12/2)² × height (ft)
SQUARE:
Volume per column (ft³) = (width/12) × (breadth/12) × height (ft)
TOTAL:
Total volume = volume per column × count × 1.10 (waste)
Yards        = Total volume ÷ 27
Bags         = ceil(Total volume ÷ bag yield)
Real-World Example

Calculation In Practice

Worked example — 6 × 12 in sonotubes at 4 ft height, 80 lb bags:

  • Radius = 6 in = 0.5 ft. Area = π × 0.5² = 0.785 ft²
  • Volume per column = 0.785 × 4 = 3.14 ft³
  • Total = 6 × 3.14 = 18.85 ft³
  • With 10% waste = 20.73 ft³ ≈ 0.77 yd³
  • 80 lb bags (0.60 ft³ each) = ceil(20.73 ÷ 0.60) = 35 bags
  • Bag cost: 35 × $6.75 = $236 · Ready-mix: max(0.77, 1) × $180 = $180 (minimum charge)
  • → Ready-mix wins here — but for 3 columns it's opposite.

Who Should Use This Tool?

1
DIY deck and porch builders pouring sonotube piers for posts and beams.
2
Fence contractors and homeowners setting wood or metal fence posts in concrete.
3
Mailbox post installers needing a single small bag per post.
4
Shed and outbuilding builders using pier-and-beam foundations with sonotubes.
5
Concrete finishers estimating decorative porch columns for exterior remodels.

Technical Reference

Standard sonotube diameters: 4, 6, 8, 10, 12, 14, 16, 18, 20, 24, 30, 36, 48 inches. Most Home Depot / Lowes stores stock 8–18 in. Larger sizes special-order.

Volume per linear foot (round): 6 in = 0.20 ft³, 8 in = 0.35 ft³, 10 in = 0.55 ft³, 12 in = 0.785 ft³, 14 in = 1.07 ft³, 16 in = 1.40 ft³, 18 in = 1.77 ft³, 24 in = 3.14 ft³.

Common applications: 8 in sonotube for deck footings, 10 in for deck / porch piers, 12 in for porch columns, 14–18 in for decorative and heavy loads, 24+ in for foundation piles.

Fence post rule: post hole depth = 1/3 of post height above ground. 6 ft above = 2 ft hole. Hole width = 3× post width. 4×4 post = 12 in hole.

Key Takeaways

Concrete column volume scales with the square of diameter — so a 12 in sonotube holds 4× the concrete of a 6 in sonotube at the same height. For bagged concrete, ready-mix usually becomes cheaper above ~1 yd³ total (roughly 30 × 80 lb bags).

Always add 10% waste factor (our tool does this). For structural columns carrying real loads (porch roofs, deck beams, second-story additions), have your engineer spec the column size and rebar.

Frequently Asked Questions

How much concrete for a 12 inch sonotube?
A 12 in diameter sonotube needs 0.785 ft³ per foot of height. A 12 in × 4 ft sonotube = 3.14 ft³ = about 5 × 80 lb bags or 0.12 yd³ ready-mix.
What size sonotube do I need?
8 in for deck footings (light loads), 10 in for deck / porch piers (medium), 12 in for typical porch columns, 14–18 in for decorative porch columns and heavy post loads, 24+ in for foundation piles.
How much concrete per fence post?
For a standard 8 ft fence: 10 in hole × 24 in deep = 1.09 ft³ = 2 × 60 lb bags per post. For 6 ft fence: 8 in × 18 in = 0.52 ft³ = 1 × 60 lb bag per post. Our tool computes exact amounts for any hole size.
How much concrete per post for fence?
Rule of thumb: post depth should be 1/3 of post height above ground. 6 ft above = 2 ft below = 18–24 in hole × 8–10 in diameter. Use our Round mode with hole diameter + depth + post count.
How much concrete do I need for 6 sonotubes?
Depends on diameter and height. Six 10 in × 4 ft sonotubes: 6 × 2.18 ft³ = 13.1 ft³ + 10% waste = 14.4 ft³ ≈ 24 × 80 lb bags or 0.53 yd³. Six 12 in × 4 ft: 6 × 3.14 = 18.8 ft³ + waste = 21 ft³ ≈ 35 × 80 lb bags.
Are sonotubes and concrete forms the same thing?
Sonotube is a brand name for cardboard concrete tube forms. Generic equivalents are called concrete forms, cardboard tube forms, or column forms. All work the same way — single-use cardboard forms that get stripped or buried after concrete cures.
How many bags of concrete in a 10 foot sonotube?
10 ft tall columns: 10 in diameter = 5.45 ft³ = ~10 × 80 lb bags. 12 in dia = 7.85 ft³ = ~14 × 80 lb bags. 14 in dia = 10.7 ft³ = ~19 × 80 lb bags. Above ~12 × 80 lb bags per column, ready-mix usually becomes cheaper.
What is concrete column formula?
For round columns: V = π × r² × h. For square: V = w × b × h. All dimensions in feet. Convert inches to feet (÷ 12) before multiplying. Multiply by column count and add 10% waste.
Are concrete pier blocks cheaper than sonotubes?
For small deck footings: yes — pier blocks ($5–8 each) beat a sonotube + concrete cost. For structural load paths under 10+ ft or below frost line, sonotubes with poured concrete are stronger and code-required in most jurisdictions.
Is this calculator free?
Yes — 100% free, no signup, all calculations run locally in your browser.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our specialized research and development team at ToolsACE brings together decades of collective experience in concrete estimating, sonotube forming references, and high-performance web tools.

Concrete Estimating SpecialistsSonotube Reference VerifiedSoftware Engineering Team

Disclaimer

Estimates assume solid concrete fill with no rebar / form void adjustments. Order 10% extra — our calculator includes that margin. Verify load requirements with a structural engineer for load-bearing columns.