Quick answer: cubic feet per tube = 3.1416 × (diameter in inches ÷ 24)² × depth in feet. Divide by 0.6 for 80 lb bags. A 12 in tube 4 ft deep takes 3.14 cu ft, or 6 bags of 80 lb.
How to calculate concrete for a tube
- Diameter of the tube in inches, divided by 24, gives the radius in feet.
- Volume = π × radius² × depth in feet.
- Multiply by the number of tubes and add about 10% for spillage and over-dig.
- Bags = cubic feet ÷ bag yield (0.60 cu ft per 80 lb bag); cubic yards = cubic feet ÷ 27.
Cubic feet = 3.1416 × (D in ÷ 24)² × depth (ft) × tubes
Bag yields are the typical figures printed on standard concrete premix: 0.60 cu ft for 80 lb, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb. Check your bag.
Bags of concrete per tube size (4 ft deep, no waste)
| Tube diameter | Cu ft per foot | Cu ft per 4 ft tube | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 6 in | 0.196 | 0.79 | 2 | 2 |
| 8 in | 0.349 | 1.40 | 3 | 4 |
| 10 in | 0.545 | 2.18 | 4 | 5 |
| 12 in | 0.785 | 3.14 | 6 | 7 |
| 14 in | 1.069 | 4.28 | 8 | 10 |
| 16 in | 1.396 | 5.59 | 10 | 13 |
| 18 in | 1.767 | 7.07 | 12 | 16 |
| 24 in | 3.142 | 12.57 | 21 | 28 |
Bags are rounded up per tube. For several tubes, use the calculator, because it rounds up once for the whole order.
How deep should tube footings be?
Footings must sit below the local frost line and on undisturbed soil. Your building department sets the depth, the diameter and whether a wider base is needed, and many require an inspection of the holes before you pour. The deck calculator counts posts and footings for a whole deck.
Worked examples
Deck footings
Eight 10 in tubes, 42 in deep: π × (10 ÷ 24)² × 3.5 × 8 = 15.3 cu ft = 0.57 cu yd. With 10% extra: 16.8 cu ft ÷ 0.6 = 28 bags of 80 lb.
One big pier
A 24 in tube 5 ft deep: π × 1² × 5 = 15.7 cu ft = 0.58 cu yd, or 27 bags of 80 lb before waste. Consider a small ready-mix load.
- Slabs, steps and other pours: use the concrete calculator.
- Sonotube is a trademark of Sonoco. This calculator works for any round form tube.
Frequently asked questions
How much concrete do I need for a Sonotube?
Volume = π × (diameter ÷ 2)² × depth. In feet: a 12 in tube 4 ft deep is π × 0.5² × 4 = 3.14 cu ft, which is 0.116 cu yd or 6 bags of 80 lb premix. Multiply by the number of tubes and add about 10% for spillage.
How many bags of concrete fill a 12 inch tube?
A 12 in tube holds 0.785 cu ft per foot of depth. At 0.60 cu ft per 80 lb bag, that is about 1.3 bags per foot, so a 4 ft tube takes 6 bags of 80 lb (5.2 rounded up) before waste.
How many bags for an 8 inch or 10 inch tube?
An 8 in tube holds 0.349 cu ft per foot and a 10 in tube 0.545 cu ft per foot. For a 4 ft depth that is 3 bags of 80 lb for an 8 in tube and 4 bags for a 10 in tube, before waste.
How deep should a Sonotube footing be?
Below your local frost depth and on undisturbed soil, and as deep as your building department or deck plans require. That can be 12 in in warm climates and 4 ft or more in cold ones. Most areas require a footing inspection before you pour.
What size Sonotube do I need?
The size comes from the load the post carries and your soil, so follow your deck plans or local code. Many deck footings use 8–12 in tubes. A footing base (a wider pad or a bell at the bottom) spreads the load further.
Should I use bags or ready-mix for tubes?
For a handful of tubes, 80 lb bags mixed on site are usually simplest. For more than about a yard, ready-mix is often cheaper and faster, but the truck needs to reach the holes, or you need a pump or a wheelbarrow crew.
Is this sonotube calculator free to use online?
Yes. The CalcWall Sonotube Calculator is completely free and works online in any browser, on a phone, tablet or computer. There is nothing to download and no account to create, and the math runs right in your browser, so results appear as you type.