Concrete Sonotube Calculator: Free Online Sonotube Volume Estimator

Use our free concrete sonotube calculator to determine exactly how much concrete and how many bags you need for sonotube pier and footing pours. Designed for deck builders, fence contractors, and foundation crews, this tool calculates concrete volume and the number of 80 lb bags needed for Sonotube or other cardboard form tube pours. Enter your tube diameter, depth, and quantity to get instant, accurate results.

How to use this calculator.

1. Select your tube diameter. Common residential sonotube sizes are 8, 10, 12, and 18 inches in diameter. Measure the inside diameter printed on the tube. Larger diameters provide greater bearing capacity for heavier structures.
2. Enter the footing depth. The depth should extend below the frost line in your area. In most of the US, this ranges from 12 to 60 inches. Check your local building code for the required depth.
3. Enter the quantity. If you are pouring multiple identical footings for a deck or fence, enter the total number. The calculator multiplies each tube's volume by this quantity.
4. Review your results. The calculator shows total volume in cubic yards and the number of 80 lb bags needed. For ready-mix orders, use the cubic yard value. For DIY bag mixing, use the bag count.

How do you calculate concrete volume and bags for sonotubes?

Sonotube concrete volume uses the cylinder volume formula, then converts to cubic yards and bag count.

Volume per Tube (cu ft) = π × (Diameter (in) ÷ 24)² × Depth (ft)

Total Volume (cu yd) = (Volume per Tube ÷ 27) × Quantity

80 lb Bags = Total Volume (cu yd) × 27 × 133 lb/ft³ ÷ 80 lb

Where:

• Diameter ÷ 24 converts inches to radius in feet (divide by 12 for feet, then by 2 for radius).
• 133 lb/ft³ is the approximate density of cured concrete.
• An 80 lb bag contains enough mix for approximately 0.6 cubic feet of cured concrete.

Example calculation.

Let's calculate the concrete needed for deck footings.

Scenario: You are pouring 4 sonotubes for a deck, each 18 inches in diameter and 4 feet deep.

1. Calculate volume per tube: 3.14159 × (18 ÷ 24)² × 4 = 3.14159 × 0.5625 × 4 = 7.07 cu ft per tube
2. Convert to total cubic yards: (7.07 cu ft ÷ 27) × 4 tubes = 1.05 cu yd
3. Calculate 80 lb bags: 1.05 × 27 × 133 ÷ 80 = 47.1 bags

Result: You need approximately 1.25 cubic yardsof concrete or about 48 bags of 80 lb concrete mix for these four footings. That is 12 bags per tube. For 4 deep tubes, renting a mixer is strongly recommended.

Tips from the field.

• Cut tubes above grade. Extend sonotubes 2-4 inches above finished grade to prevent water from pooling around the post base and to keep wood posts out of soil contact. Trim tubes to level after concrete sets using a handsaw.
• Set the anchor bolt while concrete is wet. For deck posts, insert a J-bolt or post base anchor into the wet concrete at the center of the tube. Use a template or string line to ensure all anchors are aligned.
• Backfill before the pour when possible. Backfill around the outside of the tube before pouring concrete. The soil pressure supports the cardboard tube and reduces the chance of a blowout during the pour.
• Rod the concrete thoroughly. After pouring, use a length of rebar or a 2×4 to rod up and down through the concrete 15-20 times per tube. This eliminates air pockets that weaken the footing.

Disclaimer: This calculator provides estimates for planning purposes only. Actual concrete requirements vary based on tube diameter tolerances, hole irregularities, and spillage. Always check local building codes for minimum footing depth and diameter requirements. PavementCalculator.com assumes no liability for material overages or shortages.