To calculate the amount of concrete required for a 18-inch diameter Sonotube (assuming it’s a cylindrical form), you’ll need the height of the tube as well. The formula for the volume of a cylindrical shape Sonotube is V = πr^2h, where r is the radius (half of the diameter) and h is the height.

The number of concrete bags needed to fill a 18-inch diameter sonotube depends on height of the tube and the yields per bag of concrete. For a 4-foot (48 inches) tall sonotube with a diameter of 18 inches, you would need approximately 12 x 80 lb or 16 x 60 lb bags of concrete.

Sonotubes are cardboard tubes in which concrete is poured to form solid concrete pillars. The word Sonotube is a trademarked brand name. Other companies like Sakrete and Quikrete make their own version of a sonotube. Sakrete’s is called a form tube while Quikrete’s is a Quik-tube.

They’re all the same basic product, a round tube you pour concrete into which creates a pillar. The pillar can be underground which creates a footing or it can be above ground which is called a concrete pier.

Because sonotubes are made from cardboard, they’re single use only. If the tubes are used below grade, they’ll naturally break down over time. Cardboard is 100% biodegradable. However, if the tubes are used above grade, they can be removed after the concrete has hardened. In some cases a release agent should be used to help separate the tube from the concrete.

Sonotubes are very strong and able to withstand the weight and pressure of concrete. They’re used for a variety of concrete column applications, such as: Home or deck pilings, Goal or sign posts, Fence posts, Mailboxes or lamp posts and Footings.

How much concrete to fill 18 sonotube? A 18 inch sonotube requires 0.065 cubic yards or 1.77 cubic feet or either 4 x 60 lb or 3 x 80 lb bags of concrete to fill it one foot, while to fill it a 4 foot, you’ll need about 7.08 cubic feet (or 12 x 80 lb or 16 x 60 lb bags) of concrete.

In US, concrete are sold in bag concrete for small projects, popularly known as premix bag. A premix bag of concrete comes in 80 lb, 60 lb, 40 lb, 90 lb and 50 lb bags fast setting concrete.

To calculate how many bags of concrete you need to fill a 18 inch Sonotube, divide the amount of required concrete volume in cubic feet by bags yields in cubic feet.

Use following yields per bag: 80lb bags of concrete yields 0.60 cubic feet, 60lb bags of concrete yields 0.45 cubic feet, 30lb bags of concrete yields 0.30 cubic feet, 50lb bags of concrete yields 0.375 cubic feet, and 90lb bags of concrete yields 0.68 cubic feet.

**How much concrete do i need for a 18 inch Sonotube**

In general, a typical 18″ Sonotube requires 3 x 80 lb bags or 4 x 60 lb bags (or 1.77 cubic feet) of concrete to fill it one foot, while it takes 6 x 80 lb bags or 8 x 60 lb bags (or 3.54 cubic feet) of concrete to fill it two feet.

Similarly, a typical 18″ Sonotube requires 9 x 80 lb bags or 12 x 60 lb bags (or 5.31 cubic feet) of concrete to fill it three feet, while it takes 12 x 80 lb bags or 16 x 60 lb bags (or 7.08 cubic feet) of concrete to fill it four feet.

To determine how much concrete do you need for a 18 inch Sonotube, multiply the square footage [πD^2/4] of round tube with depth [H in feet] to get volume measurement [(πD^2/4)×H]. Volume of Sonotube is equal to volume of concrete required to fill a Sonotube.

**Here’s are the Table for how many bags of concrete needed to fill a 12 inch sonotube:**

SL.no |
Height |
Volume in Cubic feet |
No. of 80 lb bags |
No. of 60 lb bags |
No. of 50 lb bags |
No. of 40 lb bags |

1 | 1 | 1.77 | 3 | 4 | 5 | 6 |

2 | 2 | 3.54 | 6 | 8 | 9.5 | 12 |

3 | 3 | 5.31 | 9 | 12 | 14.5 | 18 |

4 | 4 | 7.08 | 12 | 16 | 19 | 24 |

**Steps to calculate how much concrete do you need to fill a 18 inch Sonotube are following:-**

1. Convert diameter of Sonotube in feet: Divide 18 inches by 12 to get into feet, like 18/12 foot

2) Estimate square footage of Sonotube: Area of Sonotube = πD^2/4, where π = 3.14, Diameter (D) = 1 foot, so putting all these value you get Square footage = (3.14 × 18/12 × 18/12)/4 = 1.77 square feet

3) Estimate volume of Sonotube in cubic feet: Volume = Square footage × depth in feet. Volume of required concrete to fill a 18 inch Sonotube per foot = 1.77 × 1 = 1.77 cubic feet, so for 4 feet height volume of Sonotube = 1.77 × 4 = 7.08 cubic feet

4) Estimate no. of bags of concrete per foot height: No. of 80lb bags of concrete = 1.77/ 0.60 = approx 3 bags, or No. of 60lb bags of concrete = 1.77 ÷ 0.45 = approx 4 bags.

5. Estimate no. of bags of concrete for four feet height: No. of 80lb bags of concrete = 7.08/ 0.60 = approx 12 bags, or No. of 60lb bags of concrete = 7.08 ÷ 0.45 = approx 16 bags.

**How much concrete do i need to fill a 18 inch Sonotube**

You will need approximately 1.77 cubic feet or either 3 x 80 lb bags or 4 x 60 lb bags of concrete to fill a 18 inch wide Sonotube per foot deep, while for 4 feet deep, 7.08 cubic feet (or 12 x 80 lb or 16 x 60 lb bags) of concrete will be required to fill a 18-inch Sonotube.

**Conclusions:**

Typically for a 18-inch wide and 4 feet tall Sonotube, you’ll need roughly 7.08 cubic feet or either 12 x 80 lb bags or 16 x 60 lb bags of concrete, while to fill 1 foot high, you will need approximately 1.77 cubic feet or either 3 x 80 lb or 4 x 60 lb bags of concrete.