Sonotube Concrete Calculator

A sonotube calculator sizes the concrete for round tube footings — the cardboard-form piers under a deck, a fence, a pergola or a mailbox. Enter the tube diameter, how deep each footing goes, and how many tubes, and it returns the total concrete plus the bags needed per tube.

Your measurements

Result

Tube footings are the most common DIY concrete job, which is why ranking competition here is almost nil. Common tube sizes are 8, 10 and 12 inches; depth is set by your frost line and the load above.

How it is calculated

Each tube is a cylinder, π·r²·depth, multiplied by the number of tubes. We also divide back out to a per-tube bag count using the 0.6 ft³ yield of an 80 lb bag, and add 10% waste because tubes are usually slightly overfilled and screeded off.

Steps

Enter the tube diameter in inches (8, 10 and 12 are standard).
Enter how deep each footing is, in feet — go below your frost line.
Enter how many tubes you are pouring.
Read the per-tube bag count — handy for buying the right number of bags.
For more than a few deep tubes, compare a small ready-mix delivery.

Worked example

Four 8-inch tubes, each 4 ft deep, hold about 1.4 cubic feet each — roughly 5.6 cubic feet or 0.21 cubic yards total, which is about 9 80 lb bags.

Common questions

How deep should a tube footing be?

Below the local frost line so it does not heave — often 36–48 inches in cold regions, less where it does not freeze. Check your code.

How many bags of concrete per tube?

The calculator shows bags per tube. As a guide, an 8-inch tube uses roughly 2 80 lb bags per foot of depth.

Sonotube or ready-mix?

For a handful of tubes, bags are easiest. For a big deck with many deep piers, a small ready-mix load can be quicker.

Do tube footings need rebar?

Often a vertical rebar cage plus an anchor bolt or post base cast into the top. The reinforcement comes from the deck or fence design.