How to use the sonotube calculator
Choose the tube diameter, how deep each pier goes below grade and how far it sticks up, and how many piers you need. The calculator gives the concrete in yards and bags, the bags for each pier if you mix them one at a time, and how many tubes to buy based on the lengths your store sells.
"Sonotube" is a brand name for cardboard concrete tube forms; other brands like QUIK-TUBE work the same way. Volume depends only on the inside diameter and height.
The formula
per pier = π × (diameter ÷ 2)² × (depth below + height above)
total = per pier × number of piers × (1 + waste)
bags = total ÷ bag yield, rounded up
Worked example: six 10 in piers, 48 in deep with 6 in above grade
- Pier height: 48 + 6 = 54 in = 4.5 ft.
- Per pier: π × (5 ÷ 12)² × 4.5 = 2.454 ft³.
- Six piers with 10% extra: 2.454 × 6 × 1.10 = 16.2 ft³, which is 0.60 yd³.
- Bags: 16.2 ÷ 0.60 = 27 bags of 80 lb, or 5 per pier if you mix each one separately.
- Tubes: each pier needs 4.5 ft, so with 4 ft tubes you need two per pier, 12 tubes. With 12 ft tubes you'd cut two piers from each and need 3.
Concrete per foot of tube
| Tube | ft³ per foot | 80 lb bags per foot |
|---|---|---|
| 6 in | 0.196 | 0.33 |
| 8 in | 0.349 | 0.58 |
| 10 in | 0.545 | 0.91 |
| 12 in | 0.785 | 1.31 |
| 16 in | 1.396 | 2.33 |
| 18 in | 1.767 | 2.95 |
| 24 in | 3.142 | 5.24 |
Setting tube forms
- Footing first. Most deck and porch codes want the tube to sit on a wider footing below the frost line, either a poured pad or a plastic bell-shaped footing form. The tube alone is a column, not a footing.
- Backfill around the tube before pouring, or brace it, so the weight of wet concrete doesn't bulge or float it.
- Pour in lifts and rod or tap the sides to remove air pockets.
- Set the anchor (J-bolt or post base) while the concrete is wet, using a string line so every bracket lines up.
- Peel the cardboard above grade once the concrete has cured; below grade it can stay.
Common mistakes
- Measuring outside diameter. Tube size is the inside diameter. The wall adds very little, so use the nominal size.
- Forgetting the part above grade. Six inches above grade on twelve piers is another 6 ft of tube.
- Undersized footings. A bigger tube doesn't make up for a footing that's too small or too shallow.
Questions people ask
How many bags of concrete for a 10 inch sonotube?
A 10 inch tube holds 0.545 cubic feet per foot of height. A 4 ft pier is 2.18 cubic feet: four 80 lb bags or five 60 lb bags.
How many bags of concrete for a 12 inch sonotube?
A 12 inch tube holds 0.785 cubic feet per foot. A 4 ft pier is 3.14 cubic feet: six 80 lb bags (5.2 rounded up) or seven 60 lb bags.
How deep should a sonotube be?
The bottom must be below your local frost depth, on undisturbed soil, and many codes and deck guides want a wider footing (a poured pad or a bell-shaped footing form) under the tube. Check your deck or building plans for the exact size.
How far should a sonotube stick out of the ground?
Commonly 2 to 6 inches above grade, enough to keep the post or bracket off wet soil. Cut the tube level after setting it.
What size sonotube do I need for a deck?
8 to 12 inch tubes are common for residential decks, sized from the load each post carries and your soil. The AWC's DCA 6 deck guide and your local code give footing sizes by joist and beam span.
Sources and assumptions
- QUIKRETE Concrete Mix (No. 1101) data sheet: 80 lb bag 0.60 ft³, 60 lb 0.45 ft³
- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide (footing sizes)
- Tube count assumes several piers can be cut from one long tube. Volume is a plain cylinder; a bell or pad footing at the base is extra.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.