Sonotube Calculator: Concrete for Round Columns

Concrete for round tube forms and columns: pick a diameter from 6 to 24 inches (150–600 mm), set the height and count, and get volume and bags.

Round tube forms (Sonotube is Sonoco's brand name; the maths works for any make) are used for deck footings, piers and columns. The concrete in each tube is π × radius² × height. A 12-inch tube 4 feet tall holds π × 0.5² × 4 = 3.14 cubic feet, about six 80 lb bags once you add 10%. Choose a common diameter or type your own, set the height and the number of tubes, and the calculator gives the volume in cubic feet, cubic yards and m³, the premixed bags of each size, and the weight. If the tube sits on a wider poured footing, work that out separately with the footing calculator and add the two.

Units
Bag sizes
Pour
in
ft
Common tube sizes:
%
Concrete
0.51 yd³

13.82 ft³ · 0.391 m³

Bags
24

80 lb bag (0.60 ft³)

Weight when mixed
2,071 lb

1.04 tons

Premixed bags needed by size
80 lb bag (0.60 ft³)24
60 lb bag (0.45 ft³)31
50 lb bag (0.375 ft³)37
40 lb bag (0.30 ft³)47
20 kg bag43
25 kg bag34
30 kg bag28
How it was worked out
  1. π × (12 in ÷ 2)² × 4 ft tall × 4 = 12.57 ft³ (0.47 yd³)
  2. Plus 10% extra = 13.82 ft³ (0.51 yd³)
  3. 80 lb bag (0.60 ft³): 13.82 ft³ ÷ 0.6 ft³ made per bag = 23.04, rounded up to 24 bags

Bag yields are typical figures: 0.30, 0.375, 0.45 and 0.60 ft³ for 40, 50, 60 and 80 lb bags, and about 108 × 20 kg bags per m³. Check the yield printed on the bag you buy. Mixed concrete is taken as 2,400 kg/m³ (about 4,050 lb per cubic yard).

Common use cases

  • Deck and porch footings in tube forms
  • Fence and gate piers, and pergola posts set in concrete columns
  • Columns for a carport or lean-to
  • Checking how many bags to buy before a deck build

How to use

  1. Choose your units. Round column is already selected.
  2. Tap a common tube size or type the diameter, then enter the height of concrete in each tube.
  3. Enter the number of tubes.
  4. Read the total volume, the bags of each size and the weight.

FAQ

How many 80 lb bags fill one foot of tube?

Before extra: about 0.58 bags for an 8-inch tube, 0.91 for 10-inch, 1.31 for 12-inch, 2.33 for 16-inch, 2.95 for 18-inch and 5.24 for 24-inch. Multiply by the height in feet and round up.

What diameter tube do I need?

That comes from the load and your local code, and deck plans usually specify it. Many decks use 8 to 12 inch tubes, often on a wider footing at the bottom. Check your plans or building department.

Does the calculator include a bell or wider footing at the base?

No, it works out straight round columns. Calculate a square pad at the base with the footing calculator and add it to the tube volume.

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