Sonotube and footing concrete calculator
Enter the diameter and height of one tube and how many you are pouring. This tool works for deck post footings, fence post footings, and pier forms, and includes a 10 percent waste allowance.
Your dimensions
Bags needed
6
Estimated bag cost: $36 to $54
Prices are typical ranges as of June 2026. Your local price will vary.
Assumptions
- •Each tube is treated as a right cylinder; the form itself is not subtracted from the volume.
- •All tubes in one calculation share the same diameter and height.
- •Bag yields are manufacturer-published values for standard 40 lb, 60 lb, and 80 lb bags of dry mix.
Questions this calculator answers
How many bags of concrete do I need for four 10 inch sonotubes, 4 feet deep?
About 16 bags of 80 lb mix, including a 10 percent waste allowance. Each tube is a cylinder: pi times radius squared times height, or about 2.18 cubic feet per tube, times 4 tubes is 8.73 cubic feet total, which rounds up to 16 bags after waste.
How much concrete does one 12 inch sonotube 3 feet tall need?
About 5 bags of 80 lb mix. A 12 inch diameter, 3 foot tall cylinder holds roughly 2.36 cubic feet, or 2.59 cubic feet with a 10 percent waste allowance.
What diameter sonotube do I need for a deck or fence post?
8 to 12 inches is common for residential deck and fence posts, but check your local building code. Required diameter and depth depend on the post load and your region's frost line.
How deep should a footing go below grade?
Deep enough to sit below your local frost line, which your building department can confirm. This calculator estimates concrete volume for the footing depth you enter; it does not set the required depth.
Should each tube be measured separately if they are different sizes?
Yes. Run the calculator once per tube size and add the bag counts together, since this tool assumes every tube in a batch shares the same diameter and height.