How much concrete a tube needs
A Sonotube is a round column form, so the concrete it holds is the volume of a cylinder: volume = π × radius² × height. For a 12-inch (1 ft) diameter tube 4 feet tall, the radius is 0.5 ft, so volume = π × 0.25 × 4 = about 3.14 cubic feet — roughly 7 sixty-pound bags of concrete mix. A tube is a cylinder, so the raw volume also comes from the cylinder volume calculator.
How to use this calculator
Enter the tube diameter in inches and the height in feet. The result shows cubic yards, cubic feet, and an estimate of 60-lb bags (each yields about 0.45 cubic foot). For several identical columns, multiply by the count. For slabs and footings instead of piers, use the concrete calculator.
Order a little extra
Add about 10% for spillage and slightly overfilling each tube. For a big pour, ready-mix delivery by the cubic yard is usually cheaper than bags. Need rebar for the columns? See the rebar calculator.
Fill the form in lifts and rod each one to drive out voids, and brace the tube so it stays plumb, because wet concrete is heavy enough to push an unbraced form out of line. Set anchor bolts or post bases while the concrete is still plastic. Post spacing along a run is worked out by the fence calculator.
Frequently asked questions
- How do I calculate concrete for a Sonotube?
- Use the cylinder volume: π × radius² × height. A 12-inch diameter, 4 ft tall tube needs about 3.14 cubic feet of concrete.
- How many bags of concrete for a Sonotube?
- A 60-lb bag yields about 0.45 cubic foot, so a 12-inch × 4 ft tube needs roughly 7 bags.
- How much extra concrete should I order?
- Add about 10% for spillage and overfill. For large pours, ready-mix by the yard is more economical than bags.
- What is a Sonotube?
- A Sonotube is a brand of cardboard tube used as a form to pour round concrete columns, piers and footings.
- How deep should the footing go?
- Below the local frost line, which is often 36 to 48 inches in cold climates and shallower further south. Check your local code, since a pier that heaves in winter will lift whatever sits on it.