Article — Concrete Tube Calculator
Concrete Tube Calculator: Bags Needed for Sonotube Pours
A 10-inch diameter Sonotube 4 feet deep needs 4 of 80-lb pre-mix bags including 10% waste — or 6 of 60-lb bags. The volume comes from V = π × r² × h: 3.14 × 0.42² × 4 = 2.18 cubic feet. Each 80-lb bag yields 0.60 cubic feet mixed; each 60-lb bag yields 0.45 cubic feet. Always round up.
What is a concrete tube?
A concrete tube is a single-use cardboard form (Sonotube brand or generic) used to pour cylindrical concrete piers and footings. The wax-impregnated cardboard tube holds the wet concrete in place until it cures, after which the tube is stripped and discarded.
Sonotube was invented in 1948 by Sonoco Products. The product transformed residential foundation work by making round concrete pours practical for non-specialists. Before Sonotube, round piers required reusable steel forms (expensive) or wood crib forms (labor intensive). Today, every home center carries the standard sizes.
The concrete tube formula
Concrete tube volume uses the cylinder formula V = π × r² × h. The radius is half the labeled diameter (inside and outside dimensions of standard Sonotubes are essentially identical due to thin cardboard walls). The height is your pour depth.
Working in inches throughout simplifies the math. A 10-inch tube 4 feet deep: π × 5² × 48 = 3,770 in³. Divide by 1,728 (cubic inches per cubic foot) to get 2.18 ft³. Or divide cubic inches by 46,656 to get cubic yards directly: 0.081 yd³.
The Sonotube cardboard form is engineered to withstand 1,800 psi of hydrostatic pressure from wet concrete — the equivalent of a 27-foot-tall column of fresh concrete pushing outward against the tube wall. Standard residential pours rarely exceed 6 feet, well within safety margin.
Concrete tube bag count
Bag count depends on tube volume and bag yield. Pre-mix concrete bags yield specific cubic foot amounts when mixed at the package water ratio. A 40-lb bag yields 0.30 ft³, a 60-lb bag yields 0.45 ft³, and an 80-lb bag yields 0.60 ft³.
Divide tube volume (in cubic feet, with waste factor) by the bag yield, then round up. For a 12-inch by 5-foot tube needing 3.93 ft³, add 10% waste (4.32 ft³), divide by 0.60 = 7.2 → 8 bags of 80 lb. Always round up — partial bags do not pour cleanly.
- 40-lb bag = 0.30 ft³ yield
- 60-lb bag = 0.45 ft³ yield
- 80-lb bag = 0.60 ft³ yield
- 90-lb bag = 0.675 ft³ yield (some brands)
- Yield is mixed volume at package water ratio
- Bags per yd³ = 27 ÷ yield
Common concrete tube sizes
Sonotubes come in diameters from 6 inches up to 48 inches, in 2-inch increments. The most common residential sizes are 8, 10, 12, and 16 inches. Lengths run from 4 feet up to 12 feet; longer pours typically splice two tubes together with a steel coupling band.
Volume scales with the square of diameter, so doubling the tube size quadruples the concrete needed per foot of depth. A 12-inch tube uses four times the concrete of a 6-inch tube per foot. Choose the smallest tube that meets your structural load requirement to minimize material cost.
Concrete tube installation
Tube installation starts with the hole. Dig below frost line on undisturbed soil per IRC R403.1.4. The hole should be slightly larger than the tube diameter to allow plumb adjustment. Pour 2 to 4 inches of compacted gravel in the bottom for drainage.
Set the tube in the hole and brace it plumb with 2×4 stakes and cross-braces. Check level on two sides before any concrete goes in. Then pour from the top in 12-inch lifts, rodding aggressively with a 1/2-inch rebar to consolidate the mix and release trapped air. For tubes over 6 feet, a small concrete vibrator works better than rodding.
Cut the tube 6 inches longer than your design pour depth. This gives you room to trim the top of the cured pour cleanly to the design height with a circular saw or angle grinder. Concrete poured to the rough tube top often has voids and weak finish — cutting back removes the bad concrete.
Concrete tube cost in 2026
Sonotube material cost runs $8 to $40 per tube depending on diameter and length. A 10-inch × 4-foot tube costs about $18 at most home centers. A 16-inch × 8-foot tube runs around $55. Bulk pricing for contractor quantities cuts these prices roughly 20 percent.
Total per-footing cost including the tube, concrete, gravel base, and labor runs $40 to $80 for DIY work and $100 to $250 for contractor installation. For a 12-pier deck, expect $480 to $960 in DIY materials or $1,200 to $3,000 contractor installed.
Concrete tube frost depth
The IRC R403.1.4 requires footings extend below local frost depth on undisturbed soil. Frost depth varies dramatically by location: 0 inches in Florida, 24 inches in mid-Atlantic states, 42 inches in the upper Midwest, up to 100 inches in northern Minnesota and Maine.
A tube footing that ends above frost line will heave during winter freeze-thaw cycles. The frost-heaved footing lifts in winter and may settle differently in spring, racking the deck or structure above. Always check your jurisdiction's frost depth before ordering tubes — buy length to reach below the frost line plus 6 inches for bearing.
A footing that lifts 1 inch each winter eventually breaks structural connections at the deck rim joist. Repair requires demolishing the deck. Always design for the deepest local frost depth, not the average. Frost depth maps are published by every state building department.
Concrete tube mistakes
The biggest mistake is calling the tube size when buying bags. People underestimate volume on round shapes. A 12-inch diameter tube holds about 44% more than a 10-inch tube per foot of depth. Use this calculator before the home center trip.
The second mistake is pouring without rodding. Tall narrow tubes trap air pockets along the cardboard wall. The cured pour has invisible voids that reduce structural capacity by 20 to 40 percent. Rod every 6 inches of lift with a 1/2-inch rebar, or use a concrete vibrator for tubes over 4 feet deep.