Sonotube Calculator
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Sonotube Concrete Volume Reference
Cubic feet per tube by diameter and height.
| Diameter | 36" Tall | 48" Tall | 60" Tall | 80-lb Bags (48") |
|---|---|---|---|---|
| 6" | 0.07 | 0.10 | 0.12 | 1 |
| 8" | 0.12 | 0.17 | 0.22 | 1 |
| 10" | 0.19 | 0.27 | 0.34 | 1 |
| 12" | 0.28 | 0.39 | 0.49 | 1 |
| 14" | 0.37 | 0.53 | 0.67 | 1 |
| 16" | 0.47 | 0.70 | 0.87 | 2 |
| 18" | 0.59 | 0.88 | 1.10 | 2 |
| 20" | 0.73 | 1.09 | 1.36 | 2 |
| 24" | 1.05 | 1.57 | 1.96 | 3 |
How We Calculate This
This sonotube calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
Sonotubes (cardboard concrete forms) create cylindrical piers for decks, fences, and posts. The concrete volume is calculated using the cylinder formula.
The basic rule:
- Formula: π × (diameter/2)² × height. Convert inches to feet before calculating cubic feet
- Standard Sonotube diameters: 6", 8", 10", 12", 14", 16", 18", 20", and 24"
- Set tubes below the frost line and at least 6" above grade to protect posts from moisture
For small jobs (a few tubes), bagged concrete is convenient — just pour dry mix into the tube and add water. For larger jobs with many tubes, ordering ready-mix saves time and ensures consistent strength.
When Would You Use This Calculator?
This sonotube calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How many bags of concrete for a 12-inch Sonotube?
A 12-inch diameter Sonotube at 4 feet deep requires about 0.39 cubic feet of concrete, which is roughly 1 bag of 80-lb concrete mix. At 48 inches deep, you need about 2 bags of 60-lb mix or 1.5 bags of 80-lb mix per tube.
What diameter Sonotube do I need?
For deck posts: 12" is standard, 16" for heavy loads. For fence posts: 8-10". For pergolas: 12-14". For structural columns: 16-24". Your local building code will specify minimum sizes based on the load being supported.
How deep should Sonotubes be set?
Sonotubes must extend below the frost line, which varies by region (12" in the South to 48"+ in the North). The tube should also extend 6 inches above grade. Check your local building code for the exact requirement.
Do I need to remove the cardboard form?
The cardboard tube above ground should be removed (peel it off once concrete sets). The portion below ground can stay in place — it will eventually decompose. Some inspectors require the above-ground portion be removed.
Should I use rebar in Sonotubes?
One piece of #4 rebar placed vertically in the center of each tube is standard practice and often required by code. The rebar should extend from the bottom of the tube up through the top to connect with the post bracket hardware.
Can I pour Sonotubes in cold weather?
Concrete should not be poured when temperatures are below 40°F (4°C) or expected to drop below freezing within 24 hours. In cool weather, use insulating blankets over the tops of the tubes for the first 48 hours to help the concrete cure properly.