Sonotube 1
Number of tubes: — qty · Diameter: — in · Fill depth: — ft
Round form estimator
Sonotube Concrete Calculator
Calculate concrete for round forms by diameter, fill depth, and tube count.
Project
Formula
Inside diameter times filled height
Total volume = tube count × π × radius² × fill depth. Radius comes from the inside diameter of the form, not the carton length and not the excavation width.
Common mistake
Ordering concrete for the unused tube length
A 4-foot form that you fill only 3 feet is a 3-foot cylinder. Enter the height concrete will actually occupy. A second diameter belongs in another section so the planner does not average the piers.
Worked quantities
Round forms by diameter and fill
Each row holds one diameter and one fill height. Bag counts use the 80 lb yield after 10% waste and round up only after the tubes are totaled.
| Tubes | Inside diameter | Fill | Measured yd³ | 80 lb bags |
|---|---|---|---|---|
| 1 tube | 8 in | 4 ft | 0.05 | 3 |
| 4 tubes | 10 in | 4 ft | 0.32 | 16 |
| 6 tubes | 12 in | 4 ft | 0.70 | 35 |
| 2 tubes | 12 in | 6 ft | 0.35 | 18 |
| 3 tubes | 18 in | 5 ft | 0.98 | 49 |
Field check
Use the form's inside diameter
The concrete fills the inside of the round form. Outside diameter or the excavation diameter will overstate the cylinder unless those dimensions are intentionally the same.
Field check
Enter the filled height
A tube may extend above grade or stop short of the bottom of an excavation. Measure the actual concrete height rather than the package length of the unused form.
Field check
Separate different pier sizes
Create one section per diameter and height combination. The planner will total the sections after each cylinder is calculated, avoiding an inaccurate average diameter.
Questions
What the sonotube calculator answers
Which diameter should I use?
Use the inside diameter of the form.
Can I calculate several tube sizes?
Yes. Add another section for each diameter or fill depth.
Does the result account for reinforcement?
No. Reinforcement does not change the purchasing quantity in this estimator.
Next step
Use a post hole only when there is no form
Post hole calculator · Column calculator · Bag yield reference
Bag yields follow the cited manufacturer data. See sources and review dates.