What Is a Sonotube?
A Sonotube® is a brand of cylindrical concrete form tube manufactured by Sonoco Products. Made from multiple layers of spiral-wound fiber bonded with heavy-duty adhesive, Sonotubes provide a strong, round mold for pouring concrete columns, posts, and piers. Once the concrete cures, the tube is simply stripped away — or left in place for underground installations.
Sonotubes are widely used for:
- Deck posts and beam supports — the most common residential application
- Fence posts and light poles
- Round architectural columns for homes and commercial buildings
- Sign bases and bollards
- Pier foundations for sheds, gazebos, and porches
Note: "Sonotube" is a registered trademark of Sonoco Plastics, Inc.
How to Use This Sonotube Calculator
- Choose your unit system — Imperial (inches/feet) or Metric (cm/m).
- Enter the Sonotube diameter — this equals your target column diameter. Common sizes: 6", 8", 10", 12", 14", 16" (Imperial) or 15, 20, 25, 30, 35, 40 cm (Metric).
- Enter the column height/depth — the total length of tube you need. If the column will be partially buried, include that depth.
- Enter the number of columns you need to fill.
- Select your concrete supply method:
- Ready-Mix (Truck) — the calculator shows the total volume you need to order.
- Pre-Mixed Bags — enter the bag size, wastage %, and optional price to get the exact bag count and cost.
- Mix My Own — choose a mix ratio (cement:sand:gravel), enter material prices, and get individual material quantities and costs.
How to Calculate Concrete for Sonotubes
The volume of concrete for a cylindrical Sonotube column is calculated using the cylinder volume formula:
V = π × r² × h
Where:
- r = radius = diameter ÷ 2
- h = height of the column
- π ≈ 3.14159
Imperial example: A 10-inch diameter column, 4 feet tall:
- r = 5 in, h = 48 in
- V = π × 5² × 48 = 3,769 in³ = 2.18 ft³ = 0.081 yd³
Metric example: A 25 cm diameter column, 1.2 m tall:
- r = 12.5 cm, h = 120 cm
- V = π × 12.5² × 120 = 58,905 cm³ = 0.059 m³ = 59 L
Pre-Mixed Concrete Bag Coverage
| Bag Size | Approximate Coverage |
|---|---|
| 40 lb (Imperial) | ~0.30 ft³ |
| 60 lb (Imperial) | ~0.45 ft³ |
| 80 lb (Imperial) | ~0.60 ft³ |
| 20 kg (Metric) | ~0.0083 m³ |
| 25 kg (Metric) | ~0.0104 m³ |
| 40 kg (Metric) | ~0.0167 m³ |
Sonotube Quick Reference Chart
| Diameter | Volume per 1 ft / 30 cm | Weight of concrete per 1 ft | 80 lb bags per 4 ft column |
|---|---|---|---|
| 6" / 15 cm | 0.196 ft³ / 0.0177 m³ | 29 lbs / 13 kg | 2 |
| 8" / 20 cm | 0.349 ft³ / 0.0314 m³ | 52 lbs / 24 kg | 3 |
| 10" / 25 cm | 0.545 ft³ / 0.0491 m³ | 82 lbs / 37 kg | 4 |
| 12" / 30 cm | 0.785 ft³ / 0.0707 m³ | 118 lbs / 54 kg | 6 |
| 14" / 35 cm | 1.069 ft³ / 0.0962 m³ | 160 lbs / 73 kg | 8 |
| 16" / 40 cm | 1.396 ft³ / 0.1257 m³ | 209 lbs / 95 kg | 10 |
Concrete Mix Ratios Explained
When mixing your own concrete, the cement:sand:gravel ratio determines strength:
- 1:2:3 — Standard general-purpose mix (~3,000 psi / 20 MPa). Best for most column applications.
- 1:1.5:3 (M20) — Higher strength (~4,000 psi / 28 MPa). For load-bearing structural columns.
- 1:2:4 — Slightly weaker, economical for lightly loaded posts.
- 1:3:6 — Mass concrete, low strength, for large non-structural pours.
The calculator applies a dry volume factor of 1.54 to account for material compaction when mixing.
FAQs
- How deep should a Sonotube be set in the ground?
- Typically 6 inches (15 cm) below the local frost line. In cold climates this can be 4–6 ft (1.2–1.8 m). Check your local building code.
- Can I leave the Sonotube on after the concrete sets?
- For above-ground portions, it is usually removed after 24–48 hours. For below-grade sections, most professionals leave the tube in place since it decomposes over time without affecting structural integrity.
- How long does concrete in a Sonotube take to set?
- Initial set takes about 24–48 hours. Full cure (design strength) takes 28 days. Do not load the column until it has cured for at least 7 days.
- What is the standard Sonotube diameter for deck posts?
- 8" (20 cm) diameter tubes are standard for most residential decks. 10" and 12" are used for heavier loads or taller decks.
- How do I estimate wastage?
- A 10% wastage allowance is typical for bagged concrete pours — some material is always left in the mixer or spilled. Increase to 15% for very large or complex pours.