Calculators/Concrete

Sonotube Concrete Calculator

Estimate how many bags of concrete you may need to fill round concrete form tubes for deck piers, columns, and structural footings.

Last reviewed: June 2026

in

Enter the total length of the tube that will receive concrete.

%

Since forms are contained, waste can be lower (5%). Add more if hand-mixing causes spills.

Results update automatically as you enter measurements.

Your Material List

For this project, buy or order approximately

Use these quantities as a shopping list, supplier note, quote check, or quick jobsite material estimate.

Bags Required
3Bags
Volume per Tube
1.396ft^3
Total Volume
1.47ft^3
Total Volume
0.054yd^3
Notice: For structural footings (like load-bearing decks or building piers), always follow local building codes for required depth (frost line) and footing base sizes. Consult a professional engineer if unsure.
Note: Bag yields vary by manufacturer. Always verify the yield on the bag packaging.
Estimate note: Actual needs vary due to compaction, grading, cuts, bag yield, and supplier differences. Confirm requirements before purchasing.

Formula and Assumptions

Formula used

Tube radius in feet = diameter ÷ 2 ÷ 12. Cylinder volume = π × radius² × height. Total volume = one tube volume × number of tubes. The calculator applies your waste factor, then divides by the selected bag yield to estimate total bags.

Unit conversions

Inches are converted to feet before volume is calculated. Cubic feet are converted to cubic yards by dividing by 27. Bag counts are rounded up because stores do not sell partial bags.

Waste factor explanation

Waste factor helps account for uneven surfaces, cuts, spills, compaction, settling, and measurement differences. The right buffer depends on your project and material.

Material Assumptions and Disclaimer

Bag yield or density assumptions

  • The concrete form tube expands minimally when wet (bulging can slightly increase required concrete).
  • Standard industry average yields are used for bag sizing.

Estimate disclaimer

These tools are useful for DIY planning and quick jobsite estimates, but the results are still estimates. Verify quantities for structural work, code requirements, supplier material specs, product labels, or professional requirements before purchasing or quoting a job.

When to be careful

  • This calculator is for volumetric estimates only, not structural engineering.
  • Always set structural footings below the local frost line and size the base (belled footing or Bigfoot system) according to local soil load-bearing capacity.

Example Calculation

Filling two 10-inch diameter tubes that are each 4 feet deep. Using 80-lb bags and 5% waste:

  1. Convert diameter to radius in feet: 10 ÷ 2 ÷ 12 ≈ 0.4167 ft
  2. Volume of one cylinder: π × 0.4167² × 4 ≈ 2.181 ft^3
  3. Multiply by 2 tubes: 2.181 × 2 = 4.363 ft^3
  4. Add 5% waste: 4.363 × 1.05 ≈ 4.58 ft^3
  5. Divide by 80-lb yield: 4.58 ÷ 0.60 = 7.63 bags
  6. Round up to nearest whole bag = 8 bags.

You need 8 80-lb bags for the two tubes.

Frequently Asked Questions

How many bags of concrete for an 8-inch sonotube?

An 8-inch sonotube requires roughly 0.35 cubic feet of concrete per linear foot. That means a 4-foot deep 8-inch tube needs about 1.4 cubic feet of concrete, which is just over two 80-lb bags, or three 60-lb bags, without counting waste.

How many bags of concrete for a 12-inch sonotube?

A 12-inch tube requires 0.785 cubic feet of concrete per linear foot. A 4-foot deep 12-inch tube requires 3.14 cubic feet of concrete, which translates to about six 80-lb bags (rounding up and accounting for a small waste factor).

Do I need a flared footing at the bottom of the tube?

Many building codes require a flared footing (like a Bigfoot system or hand-dug bell) for load-bearing decks, especially in soft soil. This calculator only estimates the straight cylindrical tube section. Any flared base will require extra concrete.

Can I leave the cardboard tube in the ground?

Yes, the below-grade portion of a cardboard concrete form is usually left in the dirt where it safely degrades over time. The above-grade portion should be stripped off once the concrete cures to improve appearance and prevent moisture wicking against any wood posts.

How do I keep the tubes from floating up?

Wet concrete is dense and fluid. If water pools in the hole, or if you pour too quickly, cardboard tubes can occasionally "float" upward. Backfilling a little dirt around the exterior base before pouring, or screwing a wooden stake to the side of the tube and driving it into the earth, secures it.

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