How Much Concrete for a Sonotube? Bags & Cost

A standard 12-inch sonotube filled 4 feet deep takes about 3.46 cubic feet of concrete, roughly 6 bags of 80-lb mix or 8 bags of 60-lb mix once you add a 10% waste allowance. Smaller 8-inch tubes need as few as 3 bags per 4 feet of depth, while a wide 24-inch column can take 23 bags or more. Below is the formula, a bag count by diameter and depth, and a calculator that gives the exact number for your tube.

The formula: how much concrete fills a sonotube

A sonotube is a cylinder, so its volume is pi times the radius squared times the depth, all in feet. Since diameter is usually given in inches, divide it by 24 to get the radius in feet, then square that number before multiplying by pi and the depth.

Radius (ft) = Diameter (in) ÷ 24Volume (ft3) = π x radius2 x depth

For a 12-inch tube, the radius is 0.5 feet. At 4 feet deep that is pi times 0.25 times 4, about 3.14 cubic feet. Add 10% for spillage and an uneven hole bottom and you land at roughly 3.46 cubic feet, which rounds up to 6 bags of 80-lb concrete mix. For any diameter and depth, the sonotube calculator runs this math and returns the bag count directly.

Concrete per linear foot, by sonotube diameter

Apply current rates only to the calculated tube volume, bag count and selected product.

Tube diameter	Cubic feet per ft (+10%)	80 lb bags per ft
8 in	0.38	0.64
10 in	0.60	1.00
12 in	0.86	1.44
16 in	1.54	2.56
18 in	1.94	3.24
24 in	3.46	5.76

Multiply the bags-per-foot column by your actual hole depth and round up. A 10-inch tube 5 feet deep, for example, needs about 5 bags, while the same depth in a 16-inch tube jumps to about 13 bags.

How many bags for a 12-inch sonotube, by depth

The table is a quantity example for a 12-inch tube at entered depths, with an assumed 10% allowance. It does not state common or required footing dimensions.

Example depth	Cubic feet (+10%)	80 lb bags	60 lb bags
2 ft	1.73	3	4
3 ft	2.59	5	6
4 ft	3.46	6	8
5 ft	4.32	8	10
6 ft	5.18	9	12
8 ft	6.91	12	16

Use the approved diameter and depth, then measure the actual excavation before buying.

Does a sonotube need a separate footing pad?

A tube is formwork for a concrete pier; its diameter and depth do not prove adequate bearing, frost protection, reinforcement or connection capacity.

Use the footing and pier geometry specified for actual loads, soil and local requirements. The approved detail may use a straight shaft, a wider base or another foundation system.

Once that geometry is known, calculate the shaft and any separate pad volumes. The deck-footing quantity guide explains the arithmetic without selecting the footing.

A tape measure checking the diameter of a sonotube form beside stacked bags of concrete mix

Bags versus ready-mix: what it costs

If the same project also involves setting posts without a tube, like a fence line, the math changes slightly since the post itself displaces some volume. The breakdown in bags of concrete per fence post covers that adjustment.

Tips to avoid running short mid-pour

Measure the actual tube diameter and hole depth before buying, not the nominal size on the label. Sonotube forms sold as 12 inches can run slightly larger inside, and a hand-dug hole is rarely a perfect cylinder.

Always round every bag count up, never down. A tube running short with wet concrete already curing in the mix cannot wait for another trip to the store.

Buy one extra bag beyond the calculated total for any tube deeper than about 4 feet, since deeper pours lose more concrete to an uneven hole bottom and settling as the form fills.

By Calcnaut

Formula and declared-case checks run during the build; sources are listed for readers to review. Read our method and editorial policy.

Frequently asked questions

How many bags of concrete do I need for a sonotube?

It depends on diameter and depth: a common 12-inch tube 4 feet deep needs about 6 bags of 80-lb concrete mix, while an 8-inch tube the same depth needs only about 3 bags. Use the per-foot table above to scale to your exact hole.

How many 80 lb bags of concrete to fill a 12 inch sonotube?

A 12-inch sonotube needs about 1.4 bags of 80-lb concrete mix per linear foot of depth, so a 4-foot tube takes about 6 bags and a 6-foot tube takes about 9 bags, including a 10% waste allowance.

How much Quikrete for 12 Sonotube?

For a 12-inch sonotube 4 feet deep, plan on 6 bags of 80-lb QUIKRETE Concrete Mix or 8 bags of 60-lb mix, since the smaller bag yields less concrete per bag.

Does a 12 sonotube need a footing?

A 12-inch tube is formwork, not proof of adequate bearing or frost protection. Use the footing diameter, base shape, depth, reinforcement and connection specified for the actual loads, soil and local requirements, then calculate concrete from those approved dimensions.

How much concrete do I need for an 8 inch sonotube?

An 8-inch tube uses about 0.64 of an 80 lb bag per foot of depth before a project-specific allowance. At an illustrative 4-foot depth, round the purchase quantity up to 3 bags.

Sources and references

These references and structured source records support the method and material data used on this page.

How Much Concrete Do I Need for a Sonotube?

Key takeaways