Sonotube & Column Concrete Calculator
Concrete per pier and for the whole set of Sonotubes, including the footing bell, with the frost-line depth that decides whether the deck moves.
0.7 yd³ neat plus 10% waste
Every pier has to bear below your local frost line — commonly 36 to 48 in across the northern states and Canada, and deeper in some counties. A shallow pier heaves.
Only 0.77 yd³. Under a short-load threshold, so either price the fee in or mix 35 bags on site.
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How to work it out yourself
- 1
One tube is a cylinder
Volume is π × radius² × height. Working in the units on the form: a 12 in tube is a 6 in radius, so π × 0.5 ft × 0.5 ft × the depth in feet gives cubic feet. A 12 in tube holds 0.785 cu ft per foot of depth — a useful number to remember, because it means four feet of 12 in tube is 3.14 cu ft, or about 0.12 yards.
- 2
Multiply by the count, then divide by 27
Piers come in sets and one is never the question. Six 12 in piers at 4 ft is 18.8 cu ft, which is 0.7 cubic yards — under any supplier's minimum, which is why deck piers and the slab or footings on the same job should be poured together wherever the schedule allows.
- 3
Add the bell if there is one
A plastic footing form at the base spreads the load over a wider bearing area. A 20 in base under a 12 in tube adds roughly 1.5 cu ft per pier, which across six piers is another third of a yard. The calculator treats the bell as a cylinder rather than the true cone, so it over-orders slightly — the right direction to be wrong in when the alternative is running out with the tubes already braced.
- 4
Depth comes from the frost line, not from the deck
The pour depth to enter is the full depth of the hole, from the bottom of the bearing surface to the top of the tube. That bottom has to be below your local frost line, which is commonly 36 to 48 in across the northern states and Canada and deeper in some counties. It is the number to confirm with your building department before you dig, because it is the only one on this page that cannot be fixed afterwards.
Worked example: Six piers for a 12 × 16 deck, 48 in frost depth
| Tube diameter | 12 in — 0.785 cu ft per foot |
| Depth per pier | 4 ft |
| Shaft per pier | 0.785 × 4 = 3.14 cu ft |
| Six piers | 18.8 cu ft |
| Cubic yards | 18.8 ÷ 27 = 0.70 yd³ |
| With 10% waste | 0.77 yd³ |
Under a yard. Either combine it with another pour on the same job, price in the short-load fee, or mix 35 bags of 80 lb on site.
The tube that floats, and the one that heaves
Two failures, both invisible on the day. A tube that is not braced and backfilled properly lifts or wanders as it takes the weight of wet concrete, and you find out when the post bases do not line up. And a pier that bottoms out above the frost line will lift a deck an inch or more every winter and set it back down slightly off — the ledger pulls, the boards gap, and by the third year the client is calling you. Neither costs anything to avoid at the time and both cost a rebuild to fix. Confirm the frost depth with the building department, and brace before you pour.
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Common questions
How much concrete does a 12 inch Sonotube hold?
0.785 cubic feet per foot of depth. A 4 ft pier is 3.14 cu ft, or 0.116 cubic yards — about 5 bags of 80 lb. Six of them is 0.70 cubic yards.
How much concrete for a 10 inch tube?
0.545 cubic feet per foot of depth. A 4 ft pier is 2.18 cu ft, or 0.081 cubic yards. An 8 in tube is 0.349 cu ft per foot, and a 16 in tube is 1.40.
How deep should deck footings be?
Below the local frost line, which is commonly 36 to 48 in across the northern states and Canada and shallower in the south. Your building department publishes the number for your county and it is the one that governs — a pier that stops above it will heave every winter and take the deck with it.
How many bags of concrete for one Sonotube?
An 80 lb bag yields about 0.6 cu ft, so a 4 ft pier in a 12 in tube takes about 6 bags. Six piers is roughly 35 bags. Past about ten piers, ready-mix with a short-load fee usually beats the labour of mixing.
Do you need a footing under a Sonotube?
Usually, and often a wider one than the tube. The tube carries the load down; the footing spreads it over enough soil to hold. Whether a plastic bell form, a poured pad or the tube alone is acceptable depends on the load and your local code — check before you dig, because the hole has to be the right shape from the start.
Should you leave the cardboard tube on?
Strip what is above grade once the concrete has set, so the form does not hold water against the pier or come apart into the finished landscape. What is below grade stays; it is doing no harm and digging it out disturbs the bearing soil you just built on.
Put this calculator on your own site
Free to use anywhere — a supplier’s resources page, a builder’s blog, a trade forum answer. It works on a phone, needs no account from your visitors, and we will not change it out from under you. All we ask is that you keep the credit line underneath, which is the second half of the snippet.
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