Article — Concrete Cylinder Calculator
Concrete Cylinder Calculator: Sonotube Volume and Bags
A concrete cylinder volume equals π × r² × h, where r is radius and h is depth. A 10-inch diameter Sonotube 4 feet deep holds 2.18 cubic feet of concrete — about four 80-lb pre-mix bags including waste. Cylindrical footings dominate deck construction in North America thanks to Sonotube and similar tube forms making round pours practical.
What is a concrete cylinder?
A concrete cylinder is a cylindrical mass of concrete, typically poured into a Sonotube cardboard form, used as a structural footing or below-grade pier. Cylindrical footings transfer point loads from posts, columns, or beams directly to soil below frost depth.
The cylindrical shape distributes load evenly across the soil bearing area. Round footings also resist frost heave better than square or rectangular footings of the same volume — the curved surface gives frozen soil less to grab. This is why cylinders dominate residential deck and pergola construction in cold climates.
The concrete cylinder formula
Volume of any right circular cylinder is V = π r² h. For concrete work, the radius is half the inside diameter of the Sonotube, and the height is the pour depth. Most builders work in inches and feet, then convert to cubic yards by dividing cubic feet by 27.
The most common error is mixing units. A 10-inch diameter with a 4-foot depth means converting one before multiplying. Working in inches throughout: π × 5² × 48 = 3,770 in³ = 2.18 ft³. Working in feet throughout: π × (5/12)² × 4 = 2.18 ft³. Same answer either way, but both inputs must use the same unit.
Sonotube was invented in 1948 by Sonoco Products Company in South Carolina. The brand became so dominant that "Sonotube" is now used generically for any cardboard concrete form, the way "Kleenex" became a generic term for tissues. The original product is still made by the same family-owned company.
Common Sonotube cylinder sizes
Cardboard concrete forms come in standardized diameters from 6 inches up to 48 inches, in 2-inch increments below 24 inches. Most residential applications use 8 to 16 inches. Lengths run from 4 feet up to 12 feet; longer pours typically splice two forms together.
- 6 in = mailbox piers, light fence posts
- 8 in = small deck piers, light pergola posts
- 10 in = standard deck and pergola footings
- 12 in = heavy deck, large pergola, porch columns
- 14 in = porch columns, light structural
- 16 in+ = structural columns, foundation piers
Concrete cylinder vs column
The shape is identical, but the application differs. A concrete cylinder typically refers to the geometric form — a Sonotube footing below grade, supporting a deck post or column. A concrete column is the structural element above grade carrying axial and lateral load from beams or roof structures.
Both can be calculated with the same V = π r² h formula. The difference matters for reinforcement: cylindrical footings under 6 feet deep usually do not require rebar. Columns supporting beams almost always need at least four vertical bars and stirrups, sized per ACI 318 or the IRC.
Frost depth for cylinder footings
The single biggest factor in cylinder depth is the local frost line. The IRC R403.1.4 requires footing bottoms below frost depth on undisturbed soil. Frost depth varies from 0 inches in Florida and southern Texas to 100 inches in northern Minnesota and Maine.
A 10-inch Sonotube footing in Atlanta might only need to extend 12 inches below grade. The same footing in Minneapolis needs 60 inches, which means five times the concrete volume per footing. Always check your jurisdiction's frost depth map before estimating cubic yards.
Pouring a footing that fails frost depth check is the most common code violation on residential deck projects. Frost-heaved footings tilt and lift, racking the deck above. Repair requires demolition. Always over-engineer by 3-6 inches if soil conditions are uncertain.
Cylinder bags vs ready-mix
For a single Sonotube under 1 cubic yard total, bagged pre-mix wins. You mix as needed, no truck scheduling, no minimum order. Each 80-lb bag yields about 0.60 cubic feet mixed; each 60-lb bag yields 0.45 cubic feet. A typical 10-inch by 4-foot footing needs four 80-lb bags.
For deck projects with 8 or more footings, ready-mix becomes economical. A 12-pier deck might total 1.5 to 3 cubic yards depending on footing size and depth. That hits the short-load fee threshold but still costs less than the equivalent in bagged mix. Plan delivery time carefully — concrete loses workability after 90 minutes in the truck.
Concrete cylinder cost
Concrete material cost for cylindrical footings runs $20 to $40 per footing for typical residential sizes. A 10-inch by 4-foot footing needs 0.08 cubic yards, costing $11 to $16 in ready-mix or $20 to $28 in bagged pre-mix. Add the Sonotube form at $8 to $20.
Total installed cost runs $100 to $250 per footing including labor, excavation, and inspection. A 12-pier deck thus carries $1,200 to $3,000 in footing cost alone, before the deck framing and surface. For DIY work, material cost only is one quarter of that.
Order Sonotube length one foot longer than your pour depth. The extra protrudes above grade, lets you trim cleanly to the design height with a saw after the pour, and keeps soil from contaminating the top of the concrete during placement.
Cylinder pouring mistakes
The first mistake is pouring on disturbed or unconsolidated soil. The IRC requires footings rest on virgin soil, compacted fill, or engineered base. Pouring on freshly turned dirt invites settlement. Either dig to firm soil or compact added base to 95% Proctor density.
The second is over-deep tubes without rod or vibration. Tall narrow pours trap air and develop voids invisibly. For tubes over 4 feet, rod aggressively with a 1/2-inch rebar or use a small concrete vibrator. The third is forgetting waste factor — always order 10% more than calculated volume.