Sonotube Concrete Calculator
A 12-inch cylindrical form filled to 4 feet holds about 3.14 cubic feet, or 0.12 cubic yard, before waste. This calculator estimates straight-cylinder footing volume and compares nominal yields for 40, 50, 60, and 80 lb concrete bags. The result is material arithmetic, not footing design. Diameter is entered in inches, filled depth in feet, and hole count as a positive whole number. Waste multiplies total volume before bag division. Bag counts always round upward. Actual holes may widen, cave in, contain water or rock, or include a bell and base beyond the tube. Soil capacity, frost depth, loads, uplift, rebar, anchors, drainage, concrete strength, and local code require a project-specific design.
Quick answer
Each hole is treated as a true cylinder using pi times radius squared times depth.
What this tells you
- •Each hole is treated as a true cylinder using pi times radius squared times depth.
- •Tube diameter in inches is converted to feet before the volume math runs.
- •Bag counts round up, so you can compare common bag sizes without running short mid-pour.
- •Waste is applied after multiplying per-hole volume by the whole-number hole count.
- •Cubic yards equal cubic feet divided by 27 and display to 2 decimals.
- •The listed bag yields are fixed assumptions and may differ from the product label.
How to Use
- 1Enter the sonotube diameter in inches.
- 2Enter the hole depth in feet for the concrete-filled section.
- 3Set the number of holes or piers.
- 4Choose the bag size you plan to buy.
- 5Add a waste allowance if you want extra for spillage and uneven holes, then calculate.
- 6Measure the actual concrete-filled depth rather than gravel, void, or exposed tube height.
- 7Confirm form diameter, footing geometry, reinforcement, strength, and frost requirements from approved plans.
- 8Compare total volume with supplier minimums when deciding between bags and ready-mix.
How It Works
Formula
Per Hole Volume (cu ft) = pi x (Diameter(ft) / 2)^2 x Depth(ft)
Total Volume = Per Hole Volume x Hole Count
Total With Waste = Total Volume x (1 + Waste%)
Bags Needed = ceil(Total With Waste / Bag Yield)The calculator keeps the cylinder math exact until the final display step. Bag counts use the full unrounded volume with waste and divide by the selected bag yield, then round up to the next whole bag.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Six deck footings, 12-inch tubes, 4 feet deep
That footing layout is just under 0.77 cubic yards after waste. If you switch to 80 lb bags, the same pour needs 35 bags.
Two porch piers, 18-inch tubes, 3 feet deep
This is about 0.41 cubic yards. A larger diameter tube drives volume up fast, so double-check the hole size before you buy bags.
One 10-inch tube using default settings
The 10-inch diameter becomes 0.8333 ft and radius 0.4167 ft. Pi x radius squared x 4 is about 2.18 cu ft. Dividing by 0.60 gives 3.64, rounded up to 4 bags.
One 12-inch tube with no waste
The exact cylindrical volume is pi cubic feet. Pi / 0.60 is about 5.24, so the selected bag count rounds upward to 6.
Concrete per 4-Foot Sonotube Hole
Approximate volume and 80 lb bag count for one straight cylindrical hole before waste.
| Tube Diameter | Depth | Volume per Hole | 80 lb Bags |
|---|---|---|---|
| 8 in | 4 ft | 1.40 cu ft | 3 |
| 10 in | 4 ft | 2.18 cu ft | 4 |
| 12 in | 4 ft | 3.14 cu ft | 6 |
| 16 in | 4 ft | 5.59 cu ft | 10 |
Bag counts are rounded up and based on a nominal 0.60 cubic foot yield for each 80 lb bag.
Cylinder volume versus a buildable footing
This calculator is built for straight cylindrical pours, which is common when a full-length sonotube lines the footing hole for a deck or porch. For that setup, diameter and depth give you a clean concrete estimate that is easy to shop against bag prices or a small ready-mix order.
Real footings are not always perfect cylinders. A bell-shaped base, loose soil at the bottom, stacked tube sections, rebar cages, or a thickened pad under the tube all change the final volume. If your footing detail widens below the tube, add that extra concrete separately.
Diameter has a squared effect because the formula uses radius squared. Increasing diameter from 12 to 18 inches multiplies cylinder area by 2.25, not 1.5. Small field differences can therefore move material needs quickly.
Waste covers quantity uncertainty but does not fix an unsuitable foundation. Required depth may depend on frost, expansive soil, bearing capacity, scour, groundwater, lateral load, and uplift. Rebar cages and anchor hardware must follow the structural detail and maintain required concrete cover.
Bag yields assume proper mixing and nominal product coverage. Water content, spillage, form leakage, consolidation, and uneven excavation can change yield. For larger volumes, ready-mix scheduling, access, minimum charges, and placement time may matter more than bag arithmetic.
Common mistakes
- Entering the radius instead of the full tube diameter
- Using total hole depth when the concrete will not fill the entire hole
- Skipping the number of holes on a multi-pier deck
- Comparing bag counts without checking the bag yield printed on the mix you plan to buy
- Treating auger diameter as the finished diameter when the hole has enlarged or caved in
- Using waste percentage as a substitute for calculating a bell or spread base
- Assuming the calculator selects footing depth, concrete strength, rebar, or anchors
- Ignoring groundwater, frost, weak soil, slope, access, and local inspection requirements
Embed this calculator on your site
Drop this single line where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use with attribution.
<script src="https://calctide.com/embed.js" data-tool="sonotube-concrete-calculator" async></script>Preview the embed at /embed/sonotube-concrete-calculator/.