Enter the tube diameter, the full height and how many you are pouring. The drawing shows the row of piers, and the ticket gives bags or cubic yards for all of them.

Concrete per tube size

Volume of a round form = π × (diameter ÷ 2)² × height. Figures below are before any extra.

Tube diameter	ft³ per foot	yd³ per foot	80 lb bags per foot	80 lb bags, 4 ft tube
6 in	0.20	0.007	0.3	2
8 in	0.35	0.013	0.6	3
10 in	0.55	0.020	0.9	4
12 in	0.79	0.029	1.3	6
14 in	1.07	0.040	1.8	8
16 in	1.40	0.052	2.3	10
18 in	1.77	0.065	2.9	12
24 in	3.14	0.116	5.2	21

Measuring for tube forms

Use the tube's labelled inside diameter.
Enter the full height: depth below grade plus the part left above.
Set the quantity to the number of tubes of that size. Add another part for a different size.
If the plan calls for a footing pad under each tube, add it as its own part.

Worked example: deck piers

A deck on ten 10 in tubes, each 4 ft long (3½ ft below grade and 6 in above). One tube holds 2.18 ft³. All ten with 10% extra come to 0.89 cubic yards: 40 bags of 80 lb mix or 54 bags of 60 lb. At that size bags are the practical choice. Enter your own count and heights above and the ticket lists each pier group separately.

Choosing the tube size

The diameter and depth come from your plans or building department, based on the load each pier carries and your soil. This calculator doesn't size footings; it tells you how much concrete the size you've chosen will take.

Size matters more than it looks. Concrete per foot grows with the square of the diameter, so going from a 10 in to a 12 in tube uses (12 ÷ 10)² = 1.44 times the concrete: 44% more for every pier.

Pouring tube forms, step by step

Dig each hole to the depth your plans give, below the frost line.
Set the tube level and plumb at the right height above grade, then backfill and tamp soil around the outside so it can't float or bulge.
Pour in lifts and rod each lift with a stick or a length of rebar to release trapped air.
Set the anchor bolt or post base while the concrete is wet, and check alignment with a string line across all piers.
Let it cure as the bag instructions say before loading the piers.

Common mistakes

Only counting the buried part. Enter the full tube height, including what stays above grade.
Using the outside diameter. The concrete fills the inside; use the tube's labelled size.
One size for every pier. If corner piers are bigger, add them as a second part so the totals stay right.
Forgetting a flared base. If the plan calls for a footing pad under the tube, add it as its own part.

Questions

How many bags of concrete for a 12 inch sonotube?

A 12 in tube holds 0.79 cubic feet per foot of height. A 4 ft tube holds 3.14 cubic feet: 6 bags of 80 lb mix, before any extra.

How many bags for an 8 inch tube 4 ft long?

1.40 cubic feet, which is 3 bags of 80 lb mix or 4 bags of 60 lb mix, before any extra.

How deep should a tube form go?

Below your local frost line and to the depth your plans or building department require. Enter the full tube height, including the part above grade.

What about a flared footing at the bottom?

Add it as a second part, for example a Footing or Square hole / pier under the tube, and the ticket totals both.

Should I add extra for waste?

The calculator adds 10% by default. Holes dug by hand are rarely perfectly round, so a little extra avoids a second trip for one more bag.

Guides: How to measure for concrete · Bagged concrete vs ready-mix

Sources

Bag yields: QUIKRETE Concrete Mix No. 1101 data sheet.

Sonotube is a registered trademark of Sonoco Products Company. pourplot is independent and not affiliated with Sonoco; the calculator works for any round tube form.

Sonotube Calculator