Sonotube Calculator
Calculate concrete for Sonotube and cylindrical pier forms - cubic yards and bag counts, for any number of tubes.
Common sizes: 8, 10, 12, 14, 16, 18, 24 in.
Below the frost line, plus 2 in above grade.
All the same size. For mixed sizes, calculate each separately and add.
Your Sonotube Estimate
- Enter the tube diameter - in inches - the printed Sonotube size.
- Enter the depth - how deep each tube is filled, in inches.
- Enter the number of tubes - all the same size; mixed sizes get separate calculations.
- Set the waste factor - 10% covers spillage and the crown at the top of each tube.
- Read yards and bags - cubic yards for ready-mix, or 80/60 lb bag counts for mixing your own.
A 12 inch diameter tube 48 inches deep holds about 0.13 cubic yards of concrete - roughly 6 bags of 80 pound mix, or 8 bags of 60 pound, once you add 10 percent for the slight crown on top. The volume is pi times the radius squared times the depth. The depth that matters is set by your frost line, not the load above: the footing has to bear below it. Enter your tube size and count above.
A Tube Footing in the Ground
How Much Concrete for a Sonotube?
A Sonotube is a cylinder, so its volume is π times the radius squared times the height - not length times width like a slab. This calculator uses the true cylinder formula, multiplies by the number of tubes, adds a waste factor, and converts to cubic yards and bag counts. Using a rectangular estimate for a round tube overstates the concrete by about 27%, so the round math matters.
For bagged concrete, an 80-pound bag of mix yields about 0.6 cubic feet and a 60-pound bag about 0.45 cubic feet. The calculator rounds bags up, since you cannot buy a partial bag, and shows the per-tube volume so you can see how each pier adds up.
Concrete per Tube by Diameter and Depth
| Diameter | 36 in deep | 48 in deep | 80 lb bags (48 in) |
|---|---|---|---|
| 8 in | 0.039 yd³ | 0.052 yd³ | 3 |
| 10 in | 0.061 yd³ | 0.081 yd³ | 4 |
| 12 in | 0.087 yd³ | 0.116 yd³ | 6 |
| 16 in | 0.155 yd³ | 0.207 yd³ | 11 |
Per single tube, base volume before waste. Add about 10% when ordering bagged concrete for spillage and over-fill.
Sonotube Formulas
Cylinder volume, scaled by quantity:
Total cubic feet = per-tube × number of tubes × (1 + waste)
Cubic yards = total cubic feet ÷ 27
Bags = total cubic feet ÷ 0.6 (80 lb) or ÷ 0.45 (60 lb), rounded up
Diameter and depth are entered in inches and converted to feet internally (inches ÷ 12).
Pouring Pier Forms
Sonotubes should extend at least 2 inches above grade to keep post hardware off the ground, and the bottom must sit below the frost line on undisturbed soil or a compacted gravel pad. Flaring the bottom of the hole wider than the tube creates a bell footing that resists frost uplift - if you do this, bump the waste factor up to 15% to cover the extra volume.
Brace each tube plumb with diagonal stakes before pouring, and lightly wet the inside of the tube and surrounding soil so the dry cardboard does not pull water from the mix. Pour in 12-to-18-inch lifts, rodding each lift to remove air pockets.
Code Note
- A pier or post footing must bear below the local frost line so it cannot be lifted by frost heave - commonly around 12 inches in the warm South up to 48 inches or more in the far North. The tube diameter carries the structural load; the depth is set by frost, not by the weight above.IRC 2021 Section R403.1 - Footing Frost Depth
Next Steps
Volume figured, line up the pour and the posts:
Related Calculators
Sonotubes are the fastest way to form round footings. See the full construction calculator collection.
Frequently Asked Questions
How much concrete is in a 12-inch Sonotube?
A 12-inch diameter tube filled 48 inches deep holds about 0.116 cubic yards of concrete, or roughly 6 bags of 80 lb mix including 10% waste. At 36 inches deep it is about 0.087 cubic yards, or 5 bags. Multiply by the number of tubes for the full order.
Why is a round calculation different from a square one?
A cylinder fills only about 78.5% of the square box around it (the ratio is π over 4), so estimating a round tube as if it were a square column overstates the concrete by about 27%. This calculator uses the true cylinder volume, π times radius squared times height, so you do not over-buy.
How deep should Sonotube footings be?
Pier footings should extend below the local frost depth - typically 36 to 48 inches in northern climates and 12 to 18 inches in the south. Check your local building code for the required depth, and make sure the bottom sits on undisturbed soil or compacted gravel.
How many 80 lb bags fill a Sonotube?
An 80 lb bag of concrete mix yields about 0.6 cubic feet. Divide the tube volume in cubic feet by 0.6 and round up. For example, a 12 inch by 48 inch tube is about 3.1 cubic feet, so roughly 6 bags with waste - but bagged mix gets expensive fast, so compare to ready-mix once you pass a few tubes.
Can I calculate several piers at once?
Yes - enter the number of tubes and the calculator multiplies the per-tube volume for you, as long as they are all the same size. If your piers are different diameters or depths, run each size separately and add the cubic yards together.