Sonotube Concrete Calculator (Metric)
Enter the tube diameter in centimetres and pour height in metres to get the cubic metres of concrete and the number of 36 kg bags for a round column.
What your result means
The 36 kg bag count fills one tube of this size. Concrete volume is the column volume in cubic metres. For more than a couple of tubes, or anything over about 60 cm across, ready-mix delivered is easier than mixing bags. A bell-footed base is extra concrete, figured separately.
How to use this calculator
- Measure the Sonotube inside diameter in centimetres (or check the label).
- Measure or calculate the total height in metres from bottom of footing to top.
- Read cubic metres of concrete needed and 36 kg bag count.
- Sonotubes over 60 cm diameter usually need ready-mix delivery.
- Don't forget to figure footing concrete separately if applicable.
The formula
Convert the diameter to a radius in metres, then the column volume is pi times the radius squared times the height. A 36 kg bag yields about 0.017 m³, so divide and round up.
Worked example
A 30 cm tube poured 1.2 m tall holds about 0.08 m³, which is 5 bags of 36 kg mix.
Concrete per metre of Sonotube height
| Diameter | m³ per metre | 36 kg bags per metre |
|---|---|---|
| 20 cm | 0.031 | 2 |
| 25 cm | 0.049 | 3 |
| 30 cm | 0.071 | 5 |
| 40 cm | 0.126 | 8 |
Tips & gotchas
- A Sonotube is a cardboard form for a round concrete column.
- Standard diameters run roughly 15 to 90 cm.
- Don't pour more than about 1.2 m at once; the hydrostatic pressure can blow the form out.
- A bell-shaped base is separate concrete, so figure it on its own.
- Stake the tubes plumb. They drift while you pour.
Frequently asked questions
What is a Sonotube used for?
Forming round concrete columns for footings, deck posts, sign bases, and fence posts.
How much concrete fills a 30 cm Sonotube?
About 0.071 m³ per metre of height. Use the calculator for the total.
Can I leave the Sonotube on?
Yes if it stays buried. Above grade, strip it off after about 24 hours.
How deep should a Sonotube footing go?
Below the frost line, often 0.8 to 1.2 m depending on your climate.
What concrete mix for Sonotubes?
Standard ~20 MPa (3,000 psi) concrete is fine for most residential columns.
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