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 a registered trademark of Sonoco. 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.

The cubic-meter divisor follows from NIST conversion factors: one cubic inch is 1.638706 × 10⁻⁵ cubic meters, so one cubic meter is about 61,023.7 cubic inches. For the example above, 5,428.67 ÷ 61,023.7 ≈ 0.0890 cubic meters.

Common sonotube diameters

Sonoco's product lines span a wide range of diameters. Its Builder's Tube comes in 6, 8, 10 and 12 inch diameters for decks, fences and mailbox posts, and its commercial forms run from 6 to 60 inches. The tube can be cut to any height.

How much concrete to order

Contractors usually order somewhat more concrete than the calculated volume. The extra covers spillage, an uneven hole bottom, and small errors in the tube's actual size. The calculator reports the exact cylinder volume with no allowance added.

How many bags of concrete for a sonotube

Bagged concrete lists its yield, the volume it makes once mixed. One manufacturer's data sheet gives these figures:

• A 60 lb bag yields about 0.45 cubic feet, and an 80 lb bag about 0.60 cubic feet.

Other brands and mixes can differ, so the bag label is the figure to use.

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

Normal-weight concrete has unit weights from about 140 to 155 pounds per cubic foot. Using 150 lb/ft³ as a round figure, the 3.14 cubic foot example weighs about 3.14 × 150 ≈ 471 pounds.

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 take up only a small share of a lightly reinforced footing, so many builders ignore it. The calculator does not subtract rebar volume.

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?

Sonoco markets its 6 to 12 inch Builder's Tube for decks. The right size depends on the load and the soil. Local building codes set the minimum size and depth, so they should be checked before ordering.

How long does concrete in a sonotube need to cure?

The Quikrete data sheet says curing should continue for 5 days at 70 °F (21 °C) or higher, or 7 days at 50 to 70 °F (10 to 21 °C). It also says to protect concrete from freezing during the first 48 hours.

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.

References

1. Sonoco. Sonotube concrete forming products (brochure). Sonotube product brochure — Sonotube is a registered trademark of Sonoco; Builder's Tube 6–12 in diameters; commercial forms 6–60 in.
2. NIST. Guide for the Use of the International System of Units (SP 811), Appendix B.8. NIST SP 811 Appendix B.8 — 1 cubic inch = 1.638706 × 10⁻⁵ m³.
3. The Quikrete Companies. Concrete Mix, Product No. 1101 (data sheet). Quikrete Concrete Mix data sheet — bag yields (60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³); curing periods.
4. Federal Highway Administration. Appendix C: Proposed Revisions to the AASHTO Standard Specifications for Highway Bridges (FHWA-HRT-05-057). FHWA high-performance concrete specifications — normal-weight concrete unit weights of about 140 to 155 lb/ft³.