Sonotubes (concrete form tubes) are cardboard tubes used to pour round footings and piers for decks, porches, posts and columns. They come in standard diameters from 6 to 48 in. A typical deck footing uses an 8–12 in tube set below the frost line and filled with concrete from bags or ready-mix.
How to use the Sonotube Calculator
- Tube diameter
- Height of concrete
- Number of tubes
- Waste
- Bag size
- Price per bag
- Price per tube
- Every result field is editable: type into Total concrete and Height of concrete plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the tube diameter, enter the height of concrete in each tube, the number of tubes, the bag size and waste. The calculator finds the cylinder volume, multiplies by the quantity and divides by the yield of one bag.
Concrete per foot of tube
| Diameter | ft³ per ft | 80 lb bags per ft |
|---|---|---|
| 6 in | 0.196 | 0.33 |
| 8 in | 0.349 | 0.58 |
| 10 in | 0.545 | 0.91 |
| 12 in | 0.785 | 1.31 |
| 14 in | 1.069 | 1.78 |
| 16 in | 1.396 | 2.33 |
| 18 in | 1.767 | 2.95 |
| 24 in | 3.142 | 5.24 |
Tips for an accurate estimate
- Measure the formwork, not the drawing – forms bulge and subgrades are rarely perfectly flat, so add 5–10%.
- Below about 1 cubic yard, premixed bags are usually cheaper; above that, ready-mix saves time and gives a more consistent pour.
- Order ready-mix in quarter- or half-yard steps and ask about short-load fees for small deliveries.
- Keep fresh concrete damp for at least a week – curing matters as much as the mix for final strength.
Common mistakes to avoid
- Running short mid-pour, which leaves a weak cold joint.
- Adding extra water on site to make concrete easier to place – it lowers strength and increases cracking.
- Ignoring the volume of rebar, posts or pipes in the pour, or the gravel base under it.
Inputs explained
| Field | What to enter |
|---|---|
| Tube diameter | Choose one: 6 in, 8 in, 10 in, 12 in … |
| Height of concrete | Units: ft, m, in, yd, cm |
| Number of tubes | A number |
| Waste | In % |
| Bag size | Choose one: 40 lb bag (0.30 ft³), 50 lb bag (0.375 ft³), 60 lb bag (0.45 ft³), 80 lb bag (0.60 ft³) … |
| Price per bag | Units: /piece |
| Price per tube | Units: /piece |
What each result means
- Concrete per tube = pi÷4×[Tube diameter]^2×[Height of concrete]
- Total concrete = [Concrete per tube]×[Number of tubes]×(1 + [Waste]÷100)
- Bags of premix = ceil([Total concrete]÷[Bag size])
- Concrete weight = [Total concrete]×2400
- Cost (bags + tubes) = [Bags of premix]×[Price per bag] + [Number of tubes]×[Price per tube]
Formula
Volume per tube = π/4 × D² × HTotal = volume × number of tubes × (1 + waste)Bags = total ÷ bag yieldWorked example
Inputs — Tube diameter: 10 in; Height of concrete: 4 ft; Number of tubes: 8; Waste: 10 %; Bag size: 80 lb bag (0.60 ft³); Price per bag: $6.5 /piece; Price per tube: $15 /piece.
Results — Concrete per tube = 2.182 ft³; Total concrete = 0.711 yd³; Bags of premix = 32; Concrete weight = 2,876 lb; Cost (bags + tubes) = $328.00.
Frequently asked questions
How many bags of concrete for a 10 in Sonotube?
A 10 in tube 4 ft tall holds 2.18 ft³ – about four 80 lb bags.
How deep should a Sonotube go?
Below your local frost line (often 36–48 in in cold climates) and on undisturbed soil or a footing pad.
Can I leave the Sonotube in the ground?
Yes; below grade the cardboard simply rots away. Peel it off above grade for a clean finish.
What formula does the Sonotube Calculator use?
Volume per tube = π/4 × D² × H.