How much concrete for a tube form or cylinder?
The concrete in a round form is the volume of a cylinder. Measure the diameter and the height in inches, and divide by 1,728 (12 x 12 x 12) to get cubic feet. [1] Divide cubic feet by 27 for cubic yards. For several identical tubes, multiply by how many there are.
Formula for the volume of a cylinder
Volume = 3.14 x (diameter / 2) x (diameter / 2) x height. The same formula works for a pier, a round column or a post hole, because a tube form is just a cylinder.
NRMCA says to order about 4% to 10% more ready mixed concrete than a calculation of the plan dimensions gives. [2] We found no source for an extra on bagged concrete, so this calculator starts at the same 10% and lets you change it.
Worked example
A tube 12 in across and 48 in tall. The volume is 3.14 x (12 / 2) x (12 / 2) x 48 / 1,728 = 3.14 cubic feet. Adding 10% extra gives 3.46 cubic feet. One 80 lb bag yields 0.60 cubic feet, so 3.46 / 0.60 = 5.76, and you order 6 bags.
How much concrete per foot of tube?
Sonoco's chart for its Builder's Tube forms gives 0.20, 0.35, 0.55 and 0.80 cubic feet of concrete per foot of height for the 6, 8, 10 and 12 inch sizes, and says the diameter sizes are nominal: if it matters, you need to measure. [3] Sonoco lists standard diameters of up to 36 inches for its larger round forms. [4]
The table works the figure out for each diameter, for 80 lb bags at 0.60 cubic feet each. [5] A second maker, Sakrete, lists a yield of .6 cubic feet for its 80 lb mix. [6]
| Diameter (in) | Cubic feet per foot | Cubic yards per foot | 80 lb bags per foot |
|---|---|---|---|
| 6 | 0.196 | 0.0073 | 0.33 |
| 8 | 0.349 | 0.0129 | 0.58 |
| 10 | 0.545 | 0.0202 | 0.91 |
| 12 | 0.785 | 0.0291 | 1.31 |
| 14 | 1.069 | 0.0396 | 1.78 |
| 16 | 1.396 | 0.0517 | 2.33 |
| 18 | 1.767 | 0.0654 | 2.95 |
| 20 | 2.182 | 0.0808 | 3.64 |
| 24 | 3.142 | 0.1164 | 5.24 |
What size tube form for a post?
The tube must be wider than the post, with room for concrete all round it. We found no source for how much room, so use the hole width from the post's own setting instructions or ask your fence or deck supplier. Our fence post concrete calculator works out the concrete around a 4x4 or 6x6 post.
Sonoco's Builder's Tube forms come in 6, 8, 10 and 12 inch diameters. [3]
What is a tube form?
Sonoco describes its Builder's Tube as a tool for professionally forming round concrete supports for dozens of projects around the home, from a deck or fence to a storage shed. [3] It is a hollow round form: you fill it with concrete, and the concrete takes the round shape.
How do you cut a tube form?
Sonoco says the only preparation you may need is to cut the easy-to-handle lengths to fit the exact size of the project, and that to strip a form you cut it vertically, using a knife or power saw. [3]
Common tube sizes: concrete and bags
Cubic feet and 80 lb bags, without extra, for six diameters at three heights. The heights are examples to show the sum.
| Diameter | 24 in tall (ft³) | Bags | 48 in tall (ft³) | Bags | 96 in tall (ft³) | Bags |
|---|---|---|---|---|---|---|
| 6 in | 0.39 | 1 | 0.79 | 2 | 1.57 | 3 |
| 8 in | 0.70 | 2 | 1.40 | 3 | 2.79 | 5 |
| 10 in | 1.09 | 2 | 2.18 | 4 | 4.36 | 8 |
| 12 in | 1.57 | 3 | 3.14 | 6 | 6.28 | 11 |
| 16 in | 2.79 | 5 | 5.59 | 10 | 11.17 | 19 |
| 24 in | 6.28 | 11 | 12.57 | 21 | 25.13 | 42 |
How much concrete for a hollow cylinder?
Take the inner circle out: volume = 3.14 x ((outer diameter / 2) x (outer diameter / 2) minus (inner diameter / 2) x (inner diameter / 2)) x height. For the 12 in x 48 in example with a 6 in hole down the middle that is 2.36 cubic feet instead of 3.14 . Open Hollow, your bag and price (optional) above and enter the Inner diameter.
How much concrete for a half cylinder?
Half the volume of the full cylinder. For the 12 in x 48 in example that is 1.57 cubic feet. A square form of the same width and height, 12 in x 12 in x 48 in, takes 4.00 cubic feet, which shows how much the round shape saves.
Are tube forms necessary?
Sonoco says its forms are recognized as the most economical way to create columns for buildings, and to provide structural support and footings. [3]
We found no source saying a form is required. Ask your local building authority what your project needs.
Sonotube and Builder's Tube are registered trademarks of Sonoco, so this page calls the product a concrete tube form. [3]
Other forms
A square form takes side x side x height, in inches, divided by 1,728 for cubic feet. A round form takes the cylinder volume above. Use the larger of the figures you measure, and add your extra.
Can a tube form stand above the ground?
Sonoco says its Builder's Tube form is designed for below ground-line concrete placement, but can be used up to 3 feet above ground line for extra support, and that minimal bracing is required above 2 feet of ground line. [3] It also says not to use a mechanical vibrator when placing concrete in it.
How deep should a tube form go?
We found no source we can cite for the depth of a tube form or for the frost depth where you live. Ask your local building authority, and follow the plan or guide it accepts.
How much do tube forms and the concrete cost?
We state no price. Ask local suppliers what one tube and one bag cost, then enter the price of a bag under Hollow, your bag and price (optional) above to see the total for the bags. The site does not store the prices you type.
Common mistakes and limits
- Trusting the nominal diameter. Sonoco says diameter sizes are nominal and, if it is critical, you need to measure. [3]
- Using inches where feet belong. The calculator converts the diameter and height for you. A hand sum has to divide by 1,728, not 144.
- Buying exactly the bags. Ask your supplier how much extra to add for your job. The extra here starts at the top of the NRMCA range for ready mixed concrete.
- What this tool does not cover: reinforcement, footings, bracing, frost depth and the strength of the concrete.
Frequently asked questions
When can you remove a tube form?
Sonoco says its Builder's Tube forms are designed to be left in place. To strip one, use a release agent before pouring, and remove the form as soon as possible after a 24-hour curing period. [3]
Can a tube form get wet, or be reused?
Sonoco says to be sure a Builder's Tube form is dry before filling it with concrete, and calls these forms single-use forms. For storage it says to put tubes on an elevated platform at least 4 inches off the ground and cover them. [3]
Do tube forms need rebar?
We found no source we can cite for whether a tube needs reinforcing bar. Ask your local building authority or whoever designed the footing.
Does a tube form need a footing under it?
We found no source we can cite for whether a tube needs a footing under it, so ask your local building authority.
How much does a concrete cylinder weigh?
NRMCA says one cubic yard of concrete weighs about 4000 lb. A 12 in x 48 in cylinder is 0.116 cubic yards, which is about 465 pounds. [2]
Sources and references
- National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship (12 inches in a foot).
- National Ready Mixed Concrete Association (NRMCA). CIP 31, Ordering Ready Mixed Concrete (Concrete in Practice, PDF dated 2006, accessed November 2026). Used for: the weight of a cubic yard of concrete, and the 4% to 10% extra for ready mixed concrete.
- Sonoco. Builder's Tube concrete forms brochure (2016, accessed November 2026). Used for: the small tube sizes, the maker's concrete per foot, and the advice on use above ground, removal and storage.
- Sonoco. Concrete Forming Products brochure, round forms (accessed November 2026). Used for: the larger round form sizes.
- The QUIKRETE Companies. Data Sheet, Concrete Mix, Product No. 1101-40, -50, -60, -80, -90 (revised October 2022, accessed November 2026). Used for: the yield of each bag size.
- Oldcastle APG (Sakrete). Sakrete High-Strength Concrete Mix 80 lb Gray (accessed November 2026). Used for: a second maker's yield for an 80 lb bag.
How we use sources: methodology.
Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.