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Sonotube Calculator · https://calcnaut.com/sonotube-calculator/

Sonotube Calculator

Enter the tube diameter, height and number of tubes to get the concrete you need for round columns and pier footings, in cubic yards and bags. The formula is shown so you can check the math.

Inputs

Enter your measurements

in
ft
in
in
Optional. Base diameter of a flared bell footing. Leave 0 for a straight tube.
in
Height of the flared bell. Only used if a bell diameter larger than the tube is set.
%
Extra for bell bottoms and over-fill at the top. 5 to 10% is typical.
$/yd³
U.S. ready-mix runs roughly $125 to 160 per cubic yard in 2026. Leave 0 to skip cost.

This is an estimate, not professional advice. Check your inputs and verify the result against your plans and local building code before you build or order. See terms and disclaimer.

How this calculator works

Radius (ft) = (Diameter(in) ÷ 2) ÷ 12Volume per tube (ft³) = π × Radius² × Height(ft)Bell footing (ft³) = (π × bell height ÷ 3) × (R² + R×r + r²) (cone frustum)Total = (Volume per tube + bell) × Tubes × (1 + Waste% ÷ 100)Cubic yards = Total(ft³) ÷ 27 Bags = Total ÷ yield (80 lb ≈ 0.60 ft³)Weight (lb) = Total(ft³) × 150 (normal-weight concrete)

Enter your dimensions and the result updates instantly. A waste allowance is included so you order slightly over rather than running short mid-pour, and ready-mix is rounded up to the nearest quarter yard, which is how it is sold.

Worked example

Four 12 inch tubes, each 4 ft tall, with a 10% waste allowance. Inputs: Tube diameter 12 in, Height 4 ft, Number of tubes 4, Waste allowance 10 %. Result: 0.51 yd³ (about 24 × 80 lb bags).

Concrete for common tube sizes

Volume per single tube with no waste. Tap a size to load it (then set your tube count) above.

Slab sizePer tube (ft³)80 lb bags
8 in × 4 ft1.43Use →
10 in × 4 ft2.184Use →
12 in × 4 ft3.146Use →
12 in × 8 ft6.2811Use →
16 in × 4 ft5.5910Use →
18 in × 6 ft10.618Use →

Method & assumptions

A sonotube forms a round concrete column, so the volume of one tube is the area of its circle times its height. We take the radius in feet (the diameter in inches, halved, divided by 12), square it, multiply by pi, and then by the height. Multiplying by the number of tubes gives the total, and the waste allowance covers bell footings and the bit of over-fill at the top.

We convert to cubic yards by dividing by 27, round ready-mix up to the nearest quarter yard, and round bags up. For a handful of small piers, bagged concrete is usually easiest; once the total passes about a cubic yard, ready-mix is cheaper and faster, which the result will tell you.

If your tubes have flared bell bottoms, enter the bell base diameter and height and the calculator adds that flared volume as a cone frustum, something most calculators leave out. Deck and fence posts also need to reach below the frost line and usually carry a rebar cage, which you can size with our rebar calculator. Always confirm pier size and depth against your plans and local code.

Pro tips and common mistakes

  • Reach below the frost line. A pier that stops above frost depth will lift in winter and rack whatever sits on it. Set the bottom of the tube below your local frost line.
  • Brace and plumb the tubes. Wet concrete is heavy and will push a tube out of plumb. Brace each one and check it for plumb before and during the pour.
  • Add a rebar cage. Most structural piers want vertical rebar with ties, and a J-bolt or post base set in the wet top. Size the steel with our rebar calculator.
  • Account for bell bottoms. Flared footing forms hold extra concrete the cylinder formula does not count. Add that volume or raise the waste so you do not run short.
  • Pour in one lift where you can. Fill each tube continuously and rod or vibrate it to remove voids. Layered pours leave cold joints in a column that carries load.
How we check this
Every formula is shown in full and verified with automated tests against manufacturer spec sheets and ASTM and ACI standards. We show our work so you can check it.

Frequently asked questions

How much concrete is in a 12 inch sonotube?
A 12 inch tube has a 0.5 foot radius, so each foot of height holds about 0.785 cubic feet. A 12 inch tube 4 feet tall holds about 3.14 cubic feet, which is roughly 6 bags of 80 lb concrete.
How many bags of concrete per sonotube?
Divide the tube volume by the bag yield. An 80 lb bag yields about 0.60 cubic feet, so a 12 inch by 4 foot tube (3.14 cubic feet) takes about 6 bags. The calculator works it out for any size.
When should I use ready-mix instead of bags?
For a few small piers, bags are easiest. Once the total passes about one cubic yard (roughly 45 bags of 80 lb mix), ready-mix is cheaper and faster, and the calculator will recommend it.
Do sonotube piers need rebar?
Structural piers usually do: vertical bars with ties, plus a J-bolt or post base in the top. Size the steel with our rebar calculator and follow your local code.

References

Related calculators

Concrete Footing Calculator→Concrete Slab Calculator→Rebar Calculator→

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Concrete needed
0.51yd³
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