Sonotube Calculator
Calculate how much concrete you need for Sonotube forms, round piers and square columns. Get cubic yards, 50/60/80 lb bag counts, tube lengths and cost for any number of columns.
How Much Concrete Does a Sonotube Need? Column & Pier Guide
Sonotubes (the generic name is cardboard concrete forming tubes) are the standard way to pour round piers for decks, porches, pergolas, carports, sheds and post-frame buildings. The tube holds wet concrete in a clean cylinder from below the frost line up to just above grade, so the post base sits high and dry. Getting the concrete quantity right matters because piers are usually poured one after another from bags, and running short halfway through a tube leaves a cold joint in the middle of a structural column.
The volume of a round column is π × radius² × height. Because tube sizes are given as diameters in inches, the quickest working numbers are per linear foot: an 8" tube holds 0.35 cu ft per foot, a 10" tube 0.55 cu ft, a 12" tube 0.79 cu ft, a 16" tube 1.40 cu ft and a 24" tube 3.14 cu ft. Doubling the diameter quadruples the concrete, which is why stepping up from a 12" to a 16" tube nearly doubles your bag count.
Tube size is chosen from the load on the pier and your soil bearing capacity, not by eye. Most deck codes based on the IRC (Table R507.3.1) size footings by tributary area, and many deck posts land on a 12" pier over a wider footing pad. Lightly loaded posts such as a small landing or pergola often use 8" or 10" tubes; heavier beam posts, carports and post-frame buildings commonly use 12"–18" tubes, sometimes with a flared plastic footing base (Bigfoot-style) at the bottom to spread the load.
In 2026 US pricing, 80 lb bags of standard concrete mix run about $5.50–$7.50 at big-box stores and ready-mix is roughly $150–$185 per cubic yard before delivery fees. A 12" × 4 ft forming tube costs about $15–$22, while a 12 ft length runs about $40–$55 and can be cut into several piers. For fewer than about a cubic yard, bags are usually cheaper and easier; above that, compare a short-load ready-mix delivery, which often carries a $50–$150 small-load fee but saves hours of mixing.
The biggest field mistakes are pouring tubes that are not plumb, skipping the bracing (wet concrete can push a tube out of line or float it upward), and filling the whole tube in one go without rodding or tapping out air. Fill in 12–18" lifts, rod each lift with a piece of rebar, and tap the outside of the tube to release trapped air. Set the post anchor or J-bolt while the concrete is still workable and check its height and alignment with a string line across all piers.
Depth below grade + height above grade
How to Use This Calculator
Understanding Your Result
The total volume already includes 10% waste, so the bag count is the number to buy. If the result is close to or above 1 cubic yard, price a ready-mix short load as well — for multi-pier jobs it is often cheaper than 45+ bags and a day of mixing.
Key Formulas
Round Column Volume
Diameter ÷ 24 converts inches to a radius in feet. Multiply by the number of columns for the total.
Square Column Volume
For square forms or box-framed piers.
Bags Required
Bag yields: 50 lb = 0.375 cu ft, 60 lb = 0.45 cu ft, 80 lb = 0.6 cu ft. The 1.10 adds 10% waste.
Worked Example
A 12 × 16 ft deck with nine 12" Sonotube piers, each 4 ft tall (42" below grade plus 6" above).
- 1Radius = 12" ÷ 2 = 6" = 0.5 ft
- 2Volume per pier = π × 0.5² × 4 = 3.14 cu ft
- 3Nine piers = 3.14 × 9 = 28.27 cu ft
- 4Add 10% waste = 28.27 × 1.10 = 31.10 cu ft = 1.15 cu yd
- 580 lb bags = 31.10 ÷ 0.6 = 51.8 → 52 bags
- 6Tubes: nine 4 ft tubes, or three 12 ft tubes cut into thirds
Buy 52 × 80 lb bags (about $290–$390 at $5.50–$7.50 per bag) and nine 4 ft tubes. At 1.15 cu yd, also get a quote for a short-load ready-mix delivery.
Assumptions Behind This Estimate
- Bag yields: 80 lb = 0.6 cu ft, 60 lb = 0.45 cu ft, 50 lb = 0.375 cu ft (typical manufacturer figures)
- 10% waste for spillage and over-dug hole bottoms
- Column height is the full tube length from the bottom of the hole to the top of the pier
- Does not include a separate spread footing pad or flared base below the tube — add that volume separately
- Tubes sold in 4 ft and 12 ft lengths; 2" allowance for trimming
Concrete per Foot of Sonotube
| Tube Diameter | Cu Ft per Foot | 80 lb Bags per Foot | Bags for a 4 ft Pier |
|---|---|---|---|
| 8" | 0.35 | 0.58 | 3 |
| 10" | 0.55 | 0.91 | 4 |
| 12" | 0.79 | 1.31 | 6 |
| 14" | 1.07 | 1.78 | 8 |
| 16" | 1.40 | 2.33 | 10 |
| 18" | 1.77 | 2.95 | 12 |
| 24" | 3.14 | 5.24 | 21 |
Bag counts rounded up. Add 10% for waste before buying.
Before You Buy: Practical Advice
- Pour every pier in one session where possible, and finish each tube in one continuous fill so there are no cold joints inside a column.
- Brace each tube on two sides with scrap lumber and check plumb with a level after backfilling around it.
- Backfill and tamp soil around the outside of the tube before pouring so the cardboard does not bulge.
- Set anchors, J-bolts or post bases while the concrete is workable, using a string line to keep them aligned.
- Have the hole depth inspected before pouring if your jurisdiction requires a footing inspection.
Frequently Asked Questions
How many bags of concrete do I need for a 12 inch Sonotube?
A 12" diameter tube holds about 0.79 cubic feet of concrete per foot of height. A 4 ft tall 12" pier needs about 3.14 cu ft, which is 6 bags of 80 lb mix (0.6 cu ft each) or 9 bags of 60 lb mix before waste. Add 10% for spillage and uneven hole bottoms, so buy 6–7 bags of 80 lb mix per 4 ft pier.
How many 80 lb bags of concrete are in a yard?
An 80 lb bag yields about 0.6 cubic feet, so one cubic yard (27 cu ft) takes 45 bags. A 60 lb bag yields about 0.45 cu ft, so a yard takes 60 bags. Once a pier job reaches roughly a cubic yard, ordering ready-mix or a short-load truck is often cheaper once you count labor and mixer rental.
What size Sonotube do I need for deck footings?
It depends on the load each post carries and your soil. Many residential deck posts use a 10" or 12" tube, often on top of a wider footing pad or flared base. Larger decks, second-story decks and roof-supporting posts frequently need 12"–16" piers or bigger footings. Your local building department or plans set the minimum, so check before buying tubes.
How deep should a Sonotube be?
The bottom of the pier must sit below your local frost depth on undisturbed soil. That ranges from about 12" in the southern US to 36–48" across most northern states and 60" or more in parts of Minnesota and Alaska. Tubes usually extend 2–6" above finished grade so water drains away from the post base.
Do I need to remove the Sonotube after the concrete cures?
You only need to strip the part that is above ground, for appearance and so the cardboard does not rot and look untidy. Below grade the tube can stay in place. Wait at least 24–48 hours, then score the cardboard with a utility knife and peel it away.
Should I put rebar in a Sonotube pier?
Many inspectors and engineers require it for structural piers. A common detail is two to four vertical #4 bars running nearly the full height, kept about 2–3" from the tube wall. For tall piers or ones that resist lateral loads, follow the engineered drawings. Use our rebar calculator to price the steel.
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