Sonotube Volume Calculator | Concrete Column Volume

What is a sonotube volume calculator

A sonotube volume calculator finds how much concrete a cylindrical concrete form will hold. A sonotube is a round cardboard tube used to shape concrete into columns, deck footings, and piers. The calculator takes the tube's diameter and height and returns the volume in cubic inches, cubic feet, and cubic meters.

Sonotube is originally a brand name owned by Sonoco Products Company. Builders now use it as a general term for any round cardboard concrete form, the way many people say "Kleenex" for any facial tissue.

Sonotube volume formula

A sonotube is a cylinder, so its volume follows the standard formula for cylinder volume:

$V = \pi \times r^2 \times h$

• V is the volume
• π (pi) is about 3.14159
• r is the radius, or half the diameter
• h is the height

Because tape measures give diameter, not radius, the formula is often written using diameter (d) instead:

$V = \pi \times \left(\frac{d}{2}\right)^2 \times h$

Example

A sonotube has a diameter of 12 inches and a height of 48 inches.

1. Find the radius: r = 12 ÷ 2 = 6 inches.
2. Apply the formula: V = π × 6² × 48 = π × 36 × 48 = π × 1,728.
3. V ≈ 5,428.67 cubic inches.

Converted to cubic feet: 5,428.67 ÷ 1,728 ≈ 3.14 cubic feet. Converted to cubic yards: 3.14 ÷ 27 ≈ 0.12 cubic yards.

Converting between units

Concrete is bought by the cubic foot, cubic yard, or cubic meter, so the raw cubic-inch result usually needs converting.

Common sonotube diameters

Sonotubes come in standard round sizes, usually 6 to 48 inches across. The tube can be cut to any height.

How much concrete to order

Contractors usually order 10 to 15 percent more concrete than the calculated volume. The extra covers spillage, an uneven hole bottom, and small errors in the tube's actual size. For a hard-to-reach site, a 15 to 20 percent buffer avoids a second delivery.

How many bags of concrete for a sonotube

Bagged concrete lists its yield, the volume it makes once mixed. Two common sizes are:

• A 60 lb bag yields about 0.45 cubic feet.
• An 80 lb bag yields about 0.60 cubic feet.

For the 3.14 cubic foot example above, divide the volume by the bag yield and round up, since a partial bag cannot be bought:

• 60 lb bags: 3.14 ÷ 0.45 ≈ 6.98, so 7 bags.
• 80 lb bags: 3.14 ÷ 0.60 ≈ 5.23, so 6 bags.

Weight of concrete in a sonotube

Standard concrete weighs about 150 pounds per cubic foot. Multiplying the volume by this figure gives the approximate weight. For the 3.14 cubic foot example: 3.14 × 150 ≈ 471 pounds.

A short history of the sonotube

Before the 1940s, builders formed concrete columns with custom wooden molds or reusable metal forms, both slow to build. The Sonoco Products Company introduced a wax-coated cardboard tube in the 1940s that could be stripped away after the concrete set. It spread quickly through residential construction in the 1950s, and later versions added water-resistant coatings and printed cutting marks.

Frequently asked questions

How accurate is the sonotube volume formula?

The formula V = π × r² × h gives the exact mathematical volume of a cylinder. Real sonotubes can vary slightly in actual diameter from their labeled size, so the true volume may differ by a small amount from the calculated one.

Do I need to subtract space for rebar?

Steel reinforcement bars usually take up less than 2 to 3 percent of the tube's volume in typical residential work, so most builders ignore it. Heavily reinforced commercial columns may reduce the concrete order by 3 to 5 percent instead.

Is "sonotube" the same thing as a concrete form tube?

Sonotube is a trademark of the Sonoco Products Company. "Concrete form tube" is the generic name for any cardboard tube used for this purpose. The two terms are used interchangeably in everyday speech.

What diameter sonotube fits a typical deck footing?

Most residential deck footings use an 8 to 12 inch diameter tube. Larger decks, multi-level structures, or heavier loads may call for 16 to 18 inches. Local building codes set the minimum size and depth, so they should be checked before ordering.

How long does concrete need to cure before the form comes off?

In warm weather, above about 70°F (21°C), concrete can usually be stripped after 24 to 48 hours. Cooler weather, 40 to 70°F (4 to 21°C), often needs 3 to 7 days. Below 40°F (4°C), curing can take a week or more and may need extra precautions against freezing.

Can this calculator be used for a square post form?

No. It calculates the volume of a round cylinder. A square or rectangular form's volume is found instead by multiplying length by width by height.