Example Data Table
| Project |
Diameter |
Depth |
Count |
Waste |
Bag Yield |
| Deck piers |
12 in |
48 in |
6 |
10% |
0.60 cu ft |
| Fence posts |
8 in |
36 in |
12 |
8% |
0.45 cu ft |
| Porch supports |
16 in |
54 in |
4 |
12% |
0.60 cu ft |
Formula Used
The calculator converts all length values to feet before solving volume.
Tube volume = π × (tube diameter ÷ 2)2 × tube depth.
Footing volume = π × (footing diameter ÷ 2)2 × footing thickness.
Displacement volume = π × (post diameter ÷ 2)2 × post depth.
Net volume each = tube volume + footing volume − displacement volume.
Total volume = net volume each × number of tubes × (1 + waste percentage ÷ 100).
Bags needed = total volume ÷ wet yield per bag. The result is rounded upward.
How to Use This Calculator
Measure the inside diameter of the round form. Enter that value first.
Enter the full concrete depth. Include the height above grade if needed.
Add the number of matching forms. Use separate runs for different sizes.
Use the footing fields when each tube has a wider round base.
Use displacement fields when a post takes space inside the concrete.
Enter the wet yield from the bag label. Add bag weight and price.
Press calculate. Then download the result as CSV or PDF.
Plan Round Concrete Piers
A sonotube pier looks simple, but volume grows fast. A small diameter change can add many bags. This calculator helps you plan that material before mixing. It works for deck posts, fence posts, mailbox bases, porch columns, and small footings. Enter the tube diameter, tube depth, and tube count. Then add waste for spillage, uneven holes, and overfill. You can also include a bell or pad below each tube.
Why Bag Yield Matters
Bag yield is the amount of wet concrete made by one bag. Many concrete mixes are sold by weight, yet they cover volume. The calculator lets you enter the yield printed on the bag. This makes the estimate fit the product you have. It also supports custom bag weight and price. That helps you compare purchase cost and hauling weight.
Better Site Planning
Round tubes are measured with a cylinder formula. The result is shown in cubic feet, cubic yards, cubic meters, and liters. Bag count is rounded up because partial bags are not practical on site. The tool also estimates total dry bag weight. Use that number for delivery, lifting, and storage planning. Keep extra mix available when the ground is rough.
Common Sonotube Checks
Measure the inside diameter, not the outside label. Check depth after the hole is cleaned. Loose soil, water, and rocks can change the real volume. If tubes are cut above grade, include the full poured height. If you pour around a post, subtract the post volume manually by lowering the effective diameter or adding a negative adjustment outside this tool.
Before Buying Bags
Round every material list upward. A small surplus is usually cheaper than a second store trip. Store bags off wet ground. Cover them from rain. Mix only what you can place before it stiffens. Label each pier location, especially when depths are different before work starts safely.
Practical Advice
Always follow local code for frost depth and footing size. Structural loads vary by project. This calculator is for material estimating only. It does not approve a foundation design. For critical decks, roofs, or occupied structures, ask a qualified professional. Use fresh bags, clean water, and proper curing. Good preparation reduces waste and improves strength.
FAQs
What does this calculator estimate?
It estimates wet concrete volume for round sonotube forms. It also estimates bag count, dry bag weight, waste amount, and material cost.
Should I use inside or outside diameter?
Use the inside diameter of the form. Concrete fills the inside space, so outside measurements can overstate the volume.
Why are bags rounded up?
Concrete bags cannot be bought as exact fractions. The calculator rounds upward so the estimate is practical for purchasing.
What is bag yield?
Bag yield is the wet concrete volume one bag makes after mixing. Use the value printed on your product label.
What waste percentage should I use?
Use five to fifteen percent for many small projects. Increase it for rough holes, uneven soil, spillage, or difficult access.
Can I include a wider footing base?
Yes. Enter the footing diameter and thickness. The calculator adds that round base volume to each sonotube.
When should I use displacement fields?
Use them when a post or object occupies space inside the concrete. Enter its diameter and embedded depth.
Is this a structural design tool?
No. It estimates material quantity only. Check local codes and ask a qualified professional for load-bearing foundation design.