Sonotube Calculator — Concrete Volume & Bags

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Walk-through

How to Use This Calculator

4 steps

1

Enter the tube diameter

Pick a standard preset (8, 10, 12, 14, 16, 18, 20, or 24 inches) or type a custom diameter in inches — the widest point across the tube, not the radius.

2

Enter the fill height

Enter how deep the tube will be filled with concrete, in feet. This is usually the tube's full length above and below grade, unless you're only partially filling it.

3

Set quantity and waste

Enter how many identical tubes you're pouring, and choose a waste percentage (5% or 10% is typical) to cover spillage and uneven ground at the base of each tube.

4

Read the volume and bag count

The result updates instantly, showing cubic feet, cubic yards, and how many 80lb bags of pre-mix concrete you need. Switch to the Bags Needed tab to compare 50lb and 60lb bag sizes and estimate total cost.

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Reference

Formula & Methodology

2 formulas

Sonotube volume

Volume (ft³) = π × (Diameter ÷ 12 ÷ 2)² × Height × Quantity

A sonotube is a cylinder, so its volume follows the standard cylinder formula π × radius² × height. Diameter is entered in inches (how sonotubes are sold and measured) and divided by 12 to convert to feet, then halved to get the radius, since height is entered directly in feet. Multiplying by quantity scales the total for multiple identical tubes.

Bag count

Bags = ROUND UP(Volume with waste ÷ Yield per bag)

Pre-mix concrete bags list a cubic-foot yield once mixed with water: about 0.37 ft³ for a 50lb bag, 0.45 ft³ for a 60lb bag, and 0.6 ft³ for an 80lb bag. Dividing the total volume (including any waste percentage) by the bag's yield and rounding up gives the number of bags to buy.

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Glossary

Key Terms Explained

6 terms

Sonotube A brand-name-turned-generic term for a round, spirally-wound cardboard concrete form used to pour cylindrical concrete footings, piers, and columns. Removed after the concrete cures, or left in place below grade.

Cylinder volume The amount of space inside a cylinder, calculated as π × radius² × height. A filled sonotube is a cylinder, so this formula gives the concrete volume needed to fill it.

Cubic yard A volume unit equal to 27 cubic feet (3 ft × 3 ft × 3 ft), the standard unit ready-mix concrete trucks price and deliver by.

Concrete bags Pre-mixed bags of cement, sand, and gravel that only need water added. Sold by weight (50lb, 60lb, or 80lb) with a listed cubic-foot yield once mixed.

Footing A concrete base, often poured in a sonotube, that spreads a structure's load into stable soil below the frost line — commonly used for deck posts, fence posts, and column supports.

Form tube Another name for a sonotube or similar cylindrical concrete form — a temporary mold that holds wet concrete in a round shape until it cures.

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Scenarios

Real-World Examples

3 worked examples

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Deck builder pouring a single footing

12in tube, 4ft deep, 1 tube

Diameter 12 in Height 4 ft Quantity 1 Waste 0%

The radius is 0.5 ft, so volume = π × 0.5² × 4 ≈ 3.14 ft³, or about 0.12 cubic yards. That's small enough that bags make more sense than ordering ready-mix — about 6 bags of 80lb pre-mix (3.14 ÷ 0.6 ≈ 5.24, rounded up to 6).

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Homeowner pouring a deck's full post footings

12in tube, 4ft deep, 6 tubes

Diameter 12 in Height 4 ft Quantity 6 Waste 0%

Multiplying the single-tube volume by 6 gives about 18.85 ft³ (0.7 cubic yards) total. At 0.6 ft³ per 80lb bag, that's roughly 32 bags — around this point it's worth pricing a small ready-mix delivery against a full pallet of bags, since delivery minimums often start around 1 cubic yard.

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Contractor estimating bag cost with waste

80lb bag conversion with 10% waste

Diameter 12 in Height 4 ft Quantity 1 Waste 10%

Adding 10% waste to the 3.14 ft³ raw volume brings it to about 3.46 ft³, which needs 6 bags of 80lb mix (3.46 ÷ 0.6 ≈ 5.77, rounded up to 6) — the same bag count as with no waste in this case, since bag counts round up to whole bags regardless of the small volume difference.

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Deep Dive

Understanding the Sonotube Concrete Calculator

3 chapters · 4 min read

Sonotubes are the standard way to pour round concrete footings and piers for decks, fences, mailbox posts, and light structural columns. Getting the concrete volume right — and buying the correct number of bags — comes down to a single formula: cylinder volume.

How the Sonotube Concrete Calculator works

A sonotube filled with concrete is a cylinder, and a cylinder's volume is π × radius² × height. This calculator takes the diameter you enter in inches, converts it to feet, and halves it to get the radius, then multiplies by the fill height in feet and the number of tubes. The result is cubic feet, which is also converted to cubic yards (dividing by 27) and to bag counts using standard pre-mix concrete yields.

Inputs and what they mean

Diameter is the tube's outer width in inches — sonotubes are sold in standard sizes from 6 to 36 inches, with 8-24in covering most residential footing and post work. Height is how deep you'll actually fill the tube with concrete, in feet — measure this after the tube is set and trimmed to its final height, not the full length of tube purchased. Quantity multiplies the single-tube volume for jobs with several identical footings, like a deck with 6 post locations. Waste adds a percentage buffer (5-10% is typical) to cover spillage, an uneven hole bottom, or minor form irregularities so you don't run short mid-pour.

Limits and edge cases

This calculator assumes a straight, uniform cylinder — it does not account for a flared or belled base (common on frost footings, where the bottom widens beyond the tube diameter for extra bearing surface). If your footing design includes a bell or spread footing, add that volume separately. It also doesn't calculate rebar or reinforcement, which most local codes require for structural footings — check your jurisdiction's requirements before pouring. For very large jobs (several cubic yards or more), compare the bag cost and labor against a small ready-mix delivery, which is often more economical past roughly 1 cubic yard.

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Questions

Frequently Asked Questions

6 questions

What are standard sonotube sizes?+

Sonotubes are commonly sold in 8, 10, 12, 14, 16, 18, 20, and 24 inch diameters, in lengths typically from 4 to 12 feet. This calculator includes preset chips for each of these standard diameters, or you can type a custom size.

What is the sonotube volume formula?+

Volume = π × (Diameter ÷ 2)² × Height, using the radius in feet. Diameter is entered in inches and converted to feet before squaring, since sonotubes are sized by diameter in inches but filled to a height measured in feet.

How many bags of concrete does a sonotube need?+

An 80lb bag of pre-mix concrete yields about 0.6 cubic feet once mixed. Divide the tube's volume in cubic feet by 0.6 and round up to get the bag count. A 12in tube filled 4ft deep needs about 6 bags of 80lb mix. 60lb bags yield about 0.45 ft³ and 50lb bags about 0.37 ft³ — the Bags Needed tab compares all three.

How do I calculate concrete for multiple sonotubes?+

If every tube is the same size, use the quantity field on the Volume tab to multiply one tube's volume by the number of tubes. If you're pouring different diameters or depths, add each one individually on the Multiple Tubes tab for a combined total volume and bag count.

Should I add extra concrete for waste?+

Yes — 5-10% is typical to cover spillage, an uneven hole bottom, and minor form irregularities. Light jobs with a clean, level base can use 5%; rougher or hand-mixed jobs are safer at 10%. The waste field adds this buffer to your order automatically.

What units does this calculator use?+

Diameter in inches, height in feet, and results in cubic feet, cubic yards, and bag counts for 50lb, 60lb, and 80lb bags. The calculator converts internally, so you never need to do the inches-to-feet math yourself.

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Sonotube Concrete Calculator