Concrete Column Calculator
Work out concrete for round Sonotube columns and pier footings — bags, cubic yards, tube length and cost.
Your columns
Check your local frost line depth.
Footing height is counted within the below-grade depth entered above, not added on top of it.
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Bags or ready-mix?
Bags are the right call
Tube length planner
Mixing & weight
The short answer
Find the cylinder’s volume with π × radius² × total height, all in feet, then multiply by the number of columns you’re pouring. A single 12″ tube, 6 ft long, holds about 4.7 cu ft — roughly 8 bags of 80 lb concrete mix. Add 5–10% waste and, for a footing base like a Bigfoot form, add that cylinder’s volume too.
Concrete per column, by tube size
Figures below are per column at a 6 ft total height (above + below grade), before waste.
| Tube diameter | Volume (6 ft) | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 6″ | 1.18 cu ft | 2 | 3 |
| 8″ | 2.09 cu ft | 4 | 5 |
| 10″ | 3.27 cu ft | 6 | 8 |
| 12″ | 4.71 cu ft | 8 | 11 |
| 16″ | 8.38 cu ft | 14 | 19 |
| 20″ | 13.09 cu ft | 22 | 30 |
| 24″ | 18.85 cu ft | 32 | 42 |
Standard Sonotube sizes and typical use
| Diameter | Typical use |
|---|---|
| 6–8″ | Light deck posts, mailbox posts, sign posts |
| 10–12″ | Standard residential deck footings, fence gate posts |
| 14–16″ | Larger deck footings, porch columns |
| 18–24″ | Structural columns, heavy load footings |
Tubes are sold in 12 ft lengths and cut down on site to the height each column needs. Always check your local building code for the required footing diameter and depth — this varies by soil type, frost line and the load the column carries.
Bigfoot / widened footing base sizes
| Footing diameter | Typical tube size above | Approx. bearing area |
|---|---|---|
| 17″ | 8″ tube | 1.58 sq ft |
| 20″ | 10″ tube | 2.18 sq ft |
| 22″ | 12″ tube | 2.64 sq ft |
| 24″ | 12″ tube | 3.14 sq ft |
| 28″ | 16″ tube | 4.28 sq ft |
| 31″ | 18–20″ tube | 5.24 sq ft |
A widened footing base spreads the column’s load over more soil without a separately formed and poured footing pad — useful on deck and porch footings where digging a wide square footing isn’t practical.
How to calculate concrete for a column
- Find the total height. Height above grade plus depth below grade.
- Find the tube’s volume. π × (diameter ÷ 2)² × total height, all in feet.
- Add the footing base, if used. π × (footing diameter ÷ 2)² × footing height, as its own cylinder.
- Multiply by the number of columns. Every column in the project.
- Add waste and convert. Add 5–10%, then divide by bag yield or convert to cubic yards for ready-mix.
Worked example
Four deck footings, 8″ tubes, 4 ft above grade, 3 ft below grade, no footing base:
- Total height per column4 + 3 = 7 ft
- Tube volume per columnπ × 0.333² × 7 = 2.44 cu ft
- Plus 10% waste2.68 cu ft
- Bags per column2.68 ÷ 0.60 = 4.5 → 5 bags
- Four columns5 × 4 = 20 × 80 lb bags
That’s about 1,600 lb of material and roughly 75 minutes of mixing for one person — comfortably a bagged-concrete job.
Bags or ready-mix?
The crossover sits around half a cubic yard combined, or roughly 6–8 mid-size columns. Below that, bags are cheaper and give you full control pouring one column at a time. Above it, ready-mix becomes cost-effective and saves hours of mixing labor — but coordinating a truck around several individual tube forms takes more planning than a single slab pour.
Pouring checklist
- Dig to the required depthBelow the local frost line, or as your building code specifies.
- Add a gravel base2–3 inches under the tube improves drainage.
- Set the tube plumbBrace it securely — an out-of-plumb tube throws off every post or beam that lands on it.
- Add a footing base if usedBigfoot or similar forms attach to the bottom of the tube before backfilling.
- Place a post anchor or rebarSet anchors while the concrete is still wet, or install a rebar cage before pouring.
- Pour and consolidateRod or vibrate the pour to remove air pockets, especially in taller tubes.
- Crown the topSlightly dome the exposed top so water sheds away from the post connection.
- Cure before loading24–48 hours minimum, full strength at about 28 days.
Common mistakes
- Mixing up radius and diameterSonotube is sold by diameter. Always halve it before squaring in the volume formula.
- Forgetting the footing base adds volumeA Bigfoot or similar widened base is extra concrete on top of the tube’s own volume, not included in it.
- Digging too shallowA footing above the frost line can heave with seasonal freezing and thawing, lifting the column out of position.
- Skipping rebarAn unreinforced column is far more prone to cracking, especially in taller or heavily loaded columns.
- Rounding the total instead of per columnRound bags up per column first, then add them together — rounding only the grand total can leave individual pours short.
- Not bracing the tubeAn unbraced tube can shift or go out of plumb during the pour, especially in taller columns.
What this calculator assumes
Adjust your result if your project differs from these.
- Bag yields of 0.60, 0.45, 0.375 and 0.30 cu ft for 80, 60, 50 and 40 lb bags
- Columns treated as true cylinders (Sonotube itself is a true cylinder)
- A footing base, if used, treated as a separate cylinder at the base, not a true tapered frustum
- Footing height counted within the below-grade depth entered, not added on top of it
- Standard concrete mix, not fast-setting or high-strength products
- Water of roughly 3 quarts per 80 lb bag; mixing at about 6 minutes per 80 lb bag, per person
- Cured concrete density of about 150 lb per cubic foot
- Prices are whatever you enter; they are not live market rates
Common questions
How much concrete does a 12 inch Sonotube need?
A 12″ diameter tube, 6 feet long, holds about 4.7 cubic feet of concrete — roughly 8 bags of 80 lb concrete mix.
What size Sonotube do I need for a deck post?
8 to 12 inches is standard for residential deck footings, depending on the load and local code. Larger structural columns or heavy posts may need 16 inches or more.
How deep should a Sonotube footing be?
Deep enough to sit below the local frost line — commonly 3 to 4 feet in colder climates, shallower in areas with no frost. Always check local building code.
What is a Bigfoot footing form?
A plastic form that widens the base of a Sonotube pour into a flared footing, spreading the column’s load over a larger area of soil without needing a separately poured footing pad.
How many bags of concrete for a fence gate post?
A structural gate post in a 12″ tube, 4 ft deep, typically needs about 4 to 5 bags of 80 lb mix — more than a standard fence post, due to the wider, deeper hole.
Can I reuse a Sonotube form?
No. Sonotube is a single-use cardboard form. It’s stripped away, or left in place above grade and trimmed, once the concrete has cured.
Do I need rebar in a Sonotube column?
Yes, for most structural columns and deck footings. A single vertical rebar or a cage, centered in the pour, significantly improves the column’s strength and crack resistance.
How long does concrete take to cure in a Sonotube?
24 to 48 hours before the form can be stripped or loaded lightly, and about 28 days to reach full design strength.
Should I use bags or ready-mix for columns?
Bags are practical for a handful of columns. Above roughly half a cubic yard combined, or more than 6–8 columns, ready-mix becomes more cost-effective and far less labor.
What diameter Sonotube sizes are available?
Common sizes run 6, 8, 10, 12, 14, 16, 18, 20 and 24 inches, sold in 12 foot lengths cut down to the height needed.
How much does a Sonotube column weigh once cured?
About 150 lb per cubic foot of cured concrete. A 12″ tube, 6 ft tall, at roughly 4.7 cu ft, weighs around 700 lb once fully cured.
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Project
| Tube diameter | — |
| Height above grade | — |
| Depth below grade | — |
| Footing base | — |
| Number of columns | — |
| Waste allowance | — |
Per column
| Concrete per column | — |
| 80 lb bags per column | — |
| Tube length needed | — |
Total shopping list
| 80 lb bags | — |
| 60 lb bags | — |
| 40 lb bags | — |
| Water needed | — |
| Tube sticks (12 ft) | — |
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes cylindrical columns and standard concrete mix with yields of 0.60, 0.45, 0.375 and 0.30 cu ft for 80, 60, 50 and 40 lb bags. Confirm quantities with your supplier before buying.