Sonotube Calculator
Calculate sonotube accurately for your build. Get material quantities, waste allowances, and project cost breakdowns. Free to use with no signup required.
Formula
Volume = pi x (Diameter/2)^2 x Height
The volume of a cylinder equals pi times the radius squared times the height. Convert diameter and height to feet before calculating to get cubic feet. Divide cubic feet by 27 to get cubic yards. Each 80-lb bag of premixed concrete yields approximately 0.6 cubic feet. Concrete weighs about 150 pounds per cubic foot.
Worked Examples
Example 1: 4 Deck Footings - 12 inch
Problem: Calculate concrete needed for four 12-inch Sonotubes, 48 inches deep with 6 inches above grade.
Solution: Radius = 6 in = 0.5 ft, Height = 54 in = 4.5 ft\nVolume each = pi x 0.5^2 x 4.5 = 3.534 cu ft\nTotal = 4 x 3.534 = 14.14 cu ft = 0.524 cu yd\n80-lb bags needed = ceil(14.14 / 0.6) = 24 bags
Result: 14.14 cu ft total, 24 bags of 80-lb concrete
Example 2: 6 Post Footings - 8 inch
Problem: Calculate for six 8-inch tubes, 36 inches deep, 4 inches above grade.
Solution: Radius = 4 in = 0.333 ft, Height = 40 in = 3.333 ft\nVolume each = pi x 0.333^2 x 3.333 = 1.164 cu ft\nTotal = 6 x 1.164 = 6.98 cu ft = 0.259 cu yd\n80-lb bags = ceil(6.98 / 0.6) = 12 bags
Result: 6.98 cu ft total, 12 bags of 80-lb concrete
Frequently Asked Questions
What is a Sonotube and when should you use one?
A Sonotube is a brand-name cardboard form tube used to create cylindrical concrete piers or columns. They are commonly used for deck footings, post foundations, fence posts, and any application requiring a round concrete column. Sonotubes come in diameters from 6 to 60 inches and are typically available in 4-foot and 12-foot lengths that can be cut to size. They provide a smooth, round finish and are much easier to set up than building square forms. After the concrete cures, the cardboard form is peeled away from the above-grade portion.
How deep should Sonotube footings be?
Sonotube footings must extend below the local frost line to prevent heaving. Frost depth varies by region: 12 inches in the southern United States, 36 to 48 inches in the northern states, and up to 60 inches or more in parts of Canada and Alaska. Your local building code specifies the exact minimum depth. The tube should also extend 6 inches or more above grade to keep the wooden post away from ground moisture. A common total depth for northern climates is 48 inches below grade plus 6 inches above, for a total of 54 inches.
What size Sonotube do I need for a deck?
The required Sonotube diameter depends on the load each pier must support and the soil bearing capacity. For a typical residential deck, 10-inch or 12-inch diameter tubes are standard. A 12-inch tube has a bearing area of about 113 square inches, which at 2000 psf soil bearing can support roughly 1,570 pounds. For heavier loads like hot tubs or multi-story decks, 16-inch or 18-inch tubes may be needed. Check your local building code and have a structural analysis done if the deck will carry heavy loads.
How many bags of concrete do I need to fill a Sonotube?
The number of bags depends on the tube diameter and depth. A 12-inch diameter tube that is 48 inches deep holds about 3.14 cubic feet of concrete. An 80-pound bag of premixed concrete yields about 0.6 cubic feet, so you would need about 6 bags per tube. A 60-pound bag yields about 0.45 cubic feet, requiring about 7 bags per tube. For multiple tubes, buying ready-mix concrete by the cubic yard is often more economical and produces a more consistent pour. Always order 10% extra to account for waste and spillage.
Can I share or bookmark my calculation?
You can bookmark the calculator page in your browser. Many calculators also display a shareable result summary you can copy. The page URL stays the same so returning to it will bring you back to the same tool.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.