Sonotube Cylindrical Pier Concrete Calculator
Calculate exact concrete volume and bag requirements (80-lb and 60-lb) for round cardboard Sonotubes, cylindrical deck piers, fence post footings, and pole barn foundations. Includes individual pier breakdowns and total ready-mix yardage.
Cylinder Dimensions & Quantity
How to Calculate Cylindrical Concrete Pier Volume Manually
Sonotubes and round concrete pier forms are geometric cylinders. To calculate the volume, determine the cross-sectional circle area using the radius, multiply by the depth, multiply by the number of posts, and convert cubic feet into cubic yards or commercial bag equivalents.
$$text{Cubic Feet} = pi times left(frac{text{Diameter}}{24}right)^2 times text{Depth (ft)} times text{Quantity} times (1 + text{Waste})$$
$$text{Cubic Yards} = frac{text{Total Cubic Feet}}{27} quad Big| quad text{80-lb Bags} = leftlceil frac{text{Total Cubic Feet}}{0.60} rightrceil$$
Worked-Out Jobsite Numerical Example
Suppose you are pouring foundations for an elevated outdoor deck requiring 6 cylindrical piers. Each pier is 12 inches in diameter and 4 feet deep (extending beneath a 36-inch regional frost line), with a 10% overage allowance.
- Calculate Radius in Feet: $$12text{ inches} / 24 = 0.5text{ ft}$$.
- Calculate Single Pier Cross-Section Area: $$pi times r^2 = 3.14159 times (0.5)^2 = 0.7854text{ sq ft}$$.
- Calculate Single Pier Volume: $$0.7854text{ sq ft} times 4.0text{ ft (depth)} = 3.1416text{ cu ft}$$.
- Calculate Total Volume for 6 Piers: $$3.1416text{ cu ft} times 6 = 18.85text{ cu ft}$$.
- Apply 10% Waste Buffer: $$18.85 times 1.10 = 20.73text{ total cu ft}$$.
- Convert to Cubic Yards: $$20.73 / 27 = 0.77text{ cubic yards}$$.
- Determine Bag Count:
- 80-lb Bags: $$20.73 / 0.60 = 34.6 rightarrow mathbf{35text{ Bags}}$$.
- 60-lb Bags: $$20.73 / 0.45 = 46.1 rightarrow mathbf{47text{ Bags}}$$.
Technical Reference: Sonotube Diameter & Bag Yield Chart
This reference schedule compares standard cardboard tube diameters, cubic foot displacement per linear foot of depth, and 80-lb concrete bag counts for common residential pier depths:
| Tube Diameter (Inches) | Volume per 1 Ft Depth | 80-lb Bags per 1 Ft Depth | Volume for 4 Ft Frost Pier | 80-lb Bags for 4 Ft Pier (with 10% waste) |
|---|---|---|---|---|
| 8-Inch Tube | 0.35 cu ft | 0.58 Bags | 1.40 cu ft (0.05 yd³) | 3 Bags |
| 10-Inch Tube | 0.55 cu ft | 0.91 Bags | 2.18 cu ft (0.08 yd³) | 4 Bags |
| 12-Inch Tube | 0.79 cu ft | 1.31 Bags | 3.14 cu ft (0.12 yd³) | 6 Bags |
| 14-Inch Tube | 1.07 cu ft | 1.78 Bags | 4.28 cu ft (0.16 yd³) | 8 Bags |
| 16-Inch Tube | 1.40 cu ft | 2.33 Bags | 5.59 cu ft (0.21 yd³) | 11 Bags |
| 18-Inch Tube | 1.77 cu ft | 2.95 Bags | 7.07 cu ft (0.26 yd³) | 13 Bags |
| 24-Inch Tube | 3.14 cu ft | 5.24 Bags | 12.57 cu ft (0.47 yd³) | 23 Bags |
Practical Field Guide: Rebar Cages & Frost Heave Protection
When using a power auger to drill pier holes, the auger bit frequently caves in loose side walls, and hand cleanout scoops create a widened cavern at the bottom of the excavation. If you place a cardboard tube directly into an augered hole without backfilling dirt around the tube prior to pouring, wet concrete can burst out of the tube bottom into the void. To prevent wasting 2 to 3 extra bags per hole, secure the cardboard tube firmly, backfill and tamp native soil around the outside of the tube, or use an engineered plastic bell footing base.
Structural Rebar Reinforcement
Plain unreinforced concrete has tremendous compressive strength but low tensile and shear strength. In regions with seismic activity or freeze-thaw soil movement:
- For 10″ and 12″ piers, place at least two to four vertical #4 (1/2-inch) deformed steel rebars tied with #3 wire ties.
- Maintain a minimum of 3 inches of concrete cover between the steel bars and the outer cardboard tube wall to prevent moisture corrosion.
- Insert a certified galvanized steel post base anchor bracket (e.g., Simpson Strong-Tie) into the top wet concrete, aligning with string lines before initial set.