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Accurately estimate concrete for Sonotubes with our free online concrete Sonotube calculator. Fast, easy, and perfect for post holes and footings.
A Concrete Sonotube Calculator is a simple yet powerful tool that helps you determine how much concrete is required to fill a cylindrical form, commonly known as a Sonotube. Sonotubes are used widely for setting posts, building footings, and creating round concrete columns for decks, fences, and other structures.
Instead of manually guessing or using complex math, our calculator allows you to input a few measurements and get instant results in cubic feet, cubic yards, and even how many 80 lb bags of concrete you’ll need.
This is especially useful for builders, DIYers, and contractors who need fast and accurate estimates before purchasing materials.
To use the concrete Sonotube calculator effectively, you need to know three key measurements:
Once you enter this data into the calculator, it applies the volume formula for a cylinder to determine the total concrete needed.
The volume of concrete required for one Sonotube can be calculated using the following formula:
Volume (cubic feet) = π × (Diameter ÷ 2)² × Height ÷ 1728
Where:
Example Calculation:
Let’s say your Sonotube has a diameter of 12 inches and a height of 48 inches.
Volume = 3.1416 × (12 ÷ 2)² × 48 ÷ 1728
Volume = 3.1416 × 36 × 48 ÷ 1728
Volume ≈ 3.1416 × 1728 ÷ 1728 = 3.1416 cubic feet
So, you’ll need approximately 3.14 cubic feet of concrete per tube.
For post holes, the process is very similar. You measure the diameter and depth of the hole, assume it's cylindrical, and use the same Sonotube formula.
If you are setting multiple fence or deck posts, just multiply the result by the number of holes.
Don’t forget: You may want to add a bit extra concrete to account for spillage or uneven ground. A 10% buffer is recommended.
A 4x4 post actually measures about 3.5" x 3.5". To ensure proper support and spacing, a Sonotube with a diameter of at least 8 inches is usually recommended. However, for stronger bases, especially for decks or load-bearing structures, many builders opt for 10-inch or even 12-inch tubes.
An 80 lb bag of concrete yields about 0.6 cubic feet of concrete.
So if your Sonotube needs 3.14 cubic feet of concrete:
Number of Bags = Volume ÷ 0.6
Number of Bags = 3.14 ÷ 0.6 ≈ 5.23 bags
You’ll need approximately 6 bags of 80 lb concrete (rounding up) to fill one 12-inch diameter, 4-foot deep Sonotube.
The Concrete Sonotube Calculator is an essential tool for anyone working on construction projects that involve cylindrical concrete forms. By simply entering the diameter, height, and number of tubes, you can get fast, reliable, and accurate concrete estimates in just seconds.
Whether you're pouring footings for a deck, setting fence posts, or building a foundation, this calculator saves you time and prevents waste. No more guessing or running back to the store mid-project!
Currently, the calculator works with imperial units (inches and feet). You can convert metric to inches using a conversion tool.
Most Sonotubes are designed for one-time use, but in some cases, if carefully removed, they may be reused.
If you're working on uneven terrain, always add 10–15% extra concrete to your total estimate.
No. Larger diameter tubes (10"–16") provide better stability and are recommended for load-bearing applications.
A typical deck post should be buried 3–4 feet deep depending on local frost line and code regulations.