Concrete Tube/Sonotube Calculator

A Sonotube (concrete tube form) is a cylindrical cardboard mold used to pour concrete columns, deck footings, and fence posts — and this calculator tells you exactly how much concrete you need to fill one or more of them. Enter your tube diameter (inches), tube height (feet), and number of tubes, then select your concrete bag weight (60 or 80 lb) to get the concrete volume in cubic feet and cubic yards, bags needed, and total weight. You can also enable the rebar option to account for volume displaced by steel reinforcement.

inches

Interior diameter of the Sonotube form

feet

Height or depth of the concrete column

Total number of identical tubes to fill

Account for rebar volume displacement

Results

Concrete Volume

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Concrete Volume

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Bags Needed

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Total Weight

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Frequently Asked Questions

What is a Sonotube and what is it used for?

A Sonotube is a brand of cylindrical concrete form made from spiral-wound fiber. It's used to create round concrete columns, posts, and footings by providing a temporary mold that can be stripped away after the concrete cures.

How many bags of concrete do I need for an 8-inch Sonotube?

For an 8-inch diameter Sonotube that's 8 feet tall, you'll need approximately 11 bags of 80-lb concrete mix or 15 bags of 60-lb mix. The exact amount depends on the height of your specific application.

What sizes do Sonotubes come in?

Sonotubes are available in diameters ranging from 6 inches to 48 inches, with standard lengths up to 12 feet. Custom lengths are available for special applications.

Should I use 60-lb or 80-lb concrete bags?

80-lb bags are more cost-effective and require fewer bags total, making them ideal for larger projects. 60-lb bags are easier to handle and better for smaller projects or when physical handling is a concern.

Do I need to account for rebar when calculating concrete volume?

Yes, rebar displaces concrete volume. For large projects or when precise concrete ordering is critical, accounting for rebar displacement can save money and prevent over-ordering.

How much does a filled Sonotube weigh?

Concrete weighs approximately 150 lbs per cubic foot. A 12-inch diameter, 8-foot tall Sonotube filled with concrete would weigh around 940 lbs plus the weight of any rebar reinforcement.

Can I cut a Sonotube to a custom length?

Yes, Sonotubes can be easily cut with a circular saw or handsaw. Mark your desired length, ensure a square cut, and sand any rough edges before installation.

How do I determine the right Sonotube size for my project?

The diameter depends on your load requirements and building codes. Larger diameters provide more surface area and load capacity. Consult structural engineering guidelines or local building codes for specific requirements.