Deck Footing / Sonotube Concrete Calculator
Round form tubes (Sonotube is the best-known brand) make neat, code-friendly piers for decks, porches and pergolas. Pick a diameter, enter the depth and number of footings, and get the concrete total.
Formula
Cu ft = π × (diameter in inches ÷ 24)² × depth in feet. A 10 in tube holds 0.545 cu ft per foot of depth.
Concrete per foot of tube
| Diameter | Cu ft per ft | 80 lb bags/ft | 60 lb bags/ft | 80 lb bags for 4 ft |
|---|---|---|---|---|
| 6 in | 0.2 | 0.33 | 0.44 | 1.3 |
| 8 in | 0.35 | 0.58 | 0.78 | 2.3 |
| 10 in | 0.55 | 0.92 | 1.22 | 3.7 |
| 12 in | 0.79 | 1.32 | 1.76 | 5.3 |
| 14 in | 1.07 | 1.78 | 2.38 | 7.1 |
| 16 in | 1.4 | 2.33 | 3.11 | 9.3 |
| 18 in | 1.77 | 2.95 | 3.93 | 11.8 |
Sizing notes
- Footing size depends on the deck load and your soil. The IRC (R507) footing tables and your local building department decide it; this tool only does the concrete math.
- Many codes require a wider footing pad below the tube (a bell or a precast footing base). Add that volume separately with the slab calculator.
- Footings must reach below the frost line, which ranges from about 12 in in the South to 48 in or more in the northern states.
Frequently asked questions
How many bags of concrete for a 10 inch Sonotube?
A 10 in tube holds about 0.55 cu ft per foot. A 4 ft deep footing needs 2.2 cu ft, or 4 × 80 lb bags (3.6 rounded up).
How many bags for a 12 inch Sonotube 4 feet deep?
About 3.14 cu ft, which is 6 × 80 lb bags (5.2 rounded up) or 7 × 60 lb bags.
What size Sonotube for deck footings?
Commonly 8–12 in for small decks and 12–16 in for larger loads, but your local code and the footing tables set the minimum.
Last reviewed October 2026 by Jim Frith. These are planning estimates; confirm quantities with your supplier and follow local codes.