Sonotube Calculator
Calculate the concrete needed to fill round tube form footings: enter tube diameter, height, and count to get cubic feet, cubic yards, and 60-lb bags.
How this calculator works
A tube-form footing is a round column of concrete, so it is a cylinder. Its volume is pi times the radius squared times the height. The radius is half the tube diameter, and since diameter is usually in inches, it gets divided by 12 to work in feet.
Once you have the volume of one tube, multiply by the number of tubes for the total concrete. To turn that into bags, divide by the yield of a 60-pound bag, which is about 0.45 cubic feet, and round up because bags come whole.
Formula: Concrete per tube (cu ft) = π × (diameter ÷ 2 ÷ 12)² × height, times the number of tubes. A 60-lb bag of concrete mix yields about 0.45 cubic feet.
Worked example
One 12-inch tube, 4 ft tall:
- Radius in feet: 12 ÷ 2 ÷ 12 = 0.5 ft
- Volume: π × (0.5 ft)² × 4 ≈ 3.14 cu ft (≈0.116 cu yd)
- Bags: 3.14 ÷ 0.45 → 7 bags (60-lb)
Reference
60-lb bags per tube:
| Tube | Concrete | Bags |
|---|---|---|
| 8 in × 4 ft | ≈1.40 ft³ | 4 bags |
| 10 in × 4 ft | ≈2.18 ft³ | 5 bags |
| 12 in × 4 ft | ≈3.14 ft³ | 7 bags |
| 12 in × 8 ft | ≈6.28 ft³ | 14 bags |
How to use
Enter the tube diameter in inches, the height in feet, and how many tubes you are pouring. The calculator returns the concrete in cubic feet, cubic yards, and 60-pound bags. Use the cubic yards for a ready-mix order and the bag count for smaller pours, and add a little extra for spillage.
Weights and quantities are estimates based on typical values. Actual figures vary with material and mix — confirm with your supplier.
Frequently asked questions
How do I figure the concrete for a round tube footing?
A tube footing is a cylinder, so its volume is pi times the radius squared times the height. The radius is half the diameter, and diameter is usually given in inches, so divide by 12 to get feet. Multiply the single-tube volume by how many tubes you are pouring to get the total concrete.
How many 60-lb bags fill one tube?
A 60-pound bag of concrete mix yields about 0.45 cubic feet. Divide the tube's volume in cubic feet by 0.45 to get the bag count, then round up since you buy whole bags. A 12-inch tube 4 feet tall holds about 3.14 cubic feet, which is 3.14 divided by 0.45, or about 7 bags.
Should I use bags or ready-mix for tube footings?
Bags work well for a handful of small tubes where the total volume is modest. Once you are pouring many tubes or large diameters, the bag count climbs fast and ready-mix delivered by the cubic yard is usually easier and cheaper. This calculator gives you both cubic yards and bag count so you can compare.
Why does diameter matter so much?
Volume grows with the square of the radius, so widening the tube adds concrete quickly. Going from an 8-inch to a 12-inch tube of the same height more than doubles the concrete needed. That is why a small jump in diameter can turn a few bags per footing into many, and why it pays to check the count before buying.
Estimates only. Verify quantities with your supplier before purchasing.