What is a Sonotube used for?

Sonotube forms are used to create round concrete piers for decks, porches, fence posts, and light structures. They provide a smooth, consistent finish and minimize concrete waste.

Should I use the tube diameter or the hole diameter?

Use the Sonotube inside diameter. If you are also filling a flared "bell" base at the bottom of the excavation, calculate that volume separately and add it to your total.

How much waste should I add for Sonotubes?

5–15% is common. Use more if you are filling a widened base (footing) below the tube or expect spillage during the fill.

Concrete Foundations

Sonotube Calculator

Quickly estimate concrete volume for round piers and column forms. Calculate the total number of concrete bags required or the cubic yardage/meterage for ready-mix orders.

Sonotube Concrete Calculator

Estimate concrete volume for round piers and footings

Tube diameter

Pour height

Quantity

Waste allowance

Results

Enter dimensions above to calculate

Pier Foundation Anatomy

The calculator focuses on the concrete volume inside the form. In frost-prone areas, ensuring the tube sits below the frost line on a solid footing is critical.

Step-by-Step Formulas

1. Single Pier Volume

V = π × (D/2)² × H

A Sonotube pier is a vertical cylinder. Calculate the volume by multiplying the area of the circle (base) by the height of the concrete pour inside the tube.

2. Total Volume

Total Volume = V × Number of Piers

For projects like decks or porch supports, multiply the volume of one pier by the total count to get the aggregate volume required.

3. Waste Allowance

Order Volume = Total Volume × (1 + Waste%)

Waste covers spillage, consolidation, and variations in tube diameter or base fill. 5–15% is standard depending on your site conditions.

4. Bag Counts & Weight

Total Weight = Order Volume × Density

Standard concrete weighs ~2,322 kg/m³ (145 lb/ft³). Use the yield specs for your specific bag size (eg 40lb, 60lb, 80lb) to determine the total number of bags.

Worked Example

Deck project: Six 12-inch diameter Sonotubes, 4 feet deep (48 in), 10% waste.

Volume per pier = π × (0.5 ft)² × 4 ft ≈ 3.1416 ft³

Total Volume = 3.1416 × 6 = 18.85 ft³

Order Volume (+10% waste) = 18.85 × 1.10 ≈ 20.73 ft³

Bags required (80 lb) = 20.73 ÷ 0.60 ≈ 35 bags

Ready-mix equivalent = 20.73 ÷ 27 ≈ 0.77 cubic yards

💡 Pro tip

When filling Sonotubes, place concrete in 12-inch "lifts" and consolidate each lift with a rebar probe or vibrator. This prevents "honeycombing" (voids) on the surface of the pier. If you are using 80 lb bags, you'll need roughly one bag for every 7.2 linear inches of a 12-inch tube.

Frequently Asked Questions

What is a Sonotube used for?: Sonotube forms are used to create round concrete piers for decks, porches, fence posts, and light structures. They provide a smooth, consistent finish and minimize concrete waste.
Should I use the tube diameter or the hole diameter?: Use the Sonotube inside diameter. If you are also filling a flared "bell" base at the bottom of the excavation, calculate that volume separately and add it to your total.
How much waste should I add for Sonotubes?: 5–15% is common. Use more if you are filling a widened base below the tube or expect spillage during the fill.