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FigureCalc

Sonotube Calculator

By Uzair Arshad , Senior Civil and Structural Engineer

Last updated: June 6, 2026

Four 12 in diameter by 48 in deep Sonotubes need about 1.16 cubic yards of concrete — roughly 13 bags of 80 lb mix or 18 bags of 60 lb mix. At 2026 prices that runs $80 to $120 in bagged mix or $145 to $260 for a small ready-mix delivery. This calculator returns cubic yards, 60 lb and 80 lb bag totals, and a 2026 cost range from your tube diameter, depth, and quantity. Common pitfall: ordering exact volume — always add 10 percent for waste, overfill, and uneven excavation.

How to use this calculator

This Sonotube calculator helps you estimate concrete volume for round form footings. Enter diameter, depth, quantity, and waste factor, then the Sonotube calculator returns cubic yards, cubic feet, and bag counts.

  1. Measure the inside diameter of your tube in inches. Common sizes are 8, 10, 12, 16, and 18 inches. Use the actual tube size you plan to buy, not a rough guess.
  2. Measure required depth in inches from top of finished grade to the bottom of footing. Many cold-climate US locations require footing bottoms at 36 to 48 inches below grade to stay below frost line.
  3. Count total footing locations. For deck framing, this usually equals your number of support posts unless your plan includes special corner or beam conditions.
  4. Set waste factor. Use 5% for clean forms and controlled pours. Use 10% for most DIY jobs where tubes are hand-cut or soil irregularities can change actual depth.
  5. Click "Calculate concrete volume" to get cubic yards, cubic feet, 80 lb and 60 lb bag counts, and both bag-mix and ready-mix budget ranges.

Common Sonotube sizes and concrete volume per foot of depth

Use this quick table to sanity-check Sonotube calculator results before ordering materials.

Tube diameter Concrete per 1 ft depth Concrete per 4 ft tube Typical use
8 in0.35 cu ft1.40 cu ftLight deck and fence post footings
10 in0.55 cu ft2.18 cu ftMedium deck posts in firm soils
12 in0.79 cu ft3.14 cu ftCommon 4x4 and some 6x6 layouts
16 in1.40 cu ft5.58 cu ftHeavier beams and soft soils
18 in1.77 cu ft7.07 cu ftLarge tributary load footings

How the calculation works 

Geometry:
Radius (ft) = (Tube Diameter (in) / 12) / 2
Depth (ft) = Tube Depth (in) / 12
Volume per Tube (cu ft) = π × Radius² × Depth

Total Volume:
Total Volume (cu ft) = Volume per Tube × Number of Tubes
With Waste (cu ft) = Total Volume × (1 + Waste % / 100)
Cubic Yards = Total with Waste / 27

Bag Count:
80 lb Bags = Total with Waste / 0.60 (rounded up)
60 lb Bags = Total with Waste / 0.45 (rounded up)
Tube Diameter
Inside diameter of the Sonotube form in inches
Tube Depth
Height of the tube from grade to footing bottom in inches
Number of Tubes
Total Sonotube footings in your project
Waste %
Extra percentage for spillage and uneven tube cuts

This Sonotube calculator uses cylinder volume math, then converts the result into practical ordering units. You get cubic feet for bag planning and cubic yards for ready-mix ordering, with a waste factor added so your estimate matches real jobsite conditions.

Example calculation

Four 12 inch Sonotubes, each 48 inches deep, with 10% waste:

  • Radius = (12 / 12) / 2 = 0.5 ft
  • Depth = 48 / 12 = 4 ft
  • Volume per tube = π × 0.5² × 4 = 3.14 cu ft
  • Total volume = 3.14 × 4 = 12.57 cu ft
  • With 10% waste = 12.57 × 1.10 = 13.82 cu ft
  • Cubic yards = 13.82 / 27 = 0.51 cu yd
  • 80 lb bags = 13.82 / 0.60 = 24 bags (rounded up)
  • 60 lb bags = 13.82 / 0.45 = 31 bags (rounded up)

For a full walkthrough with size comparison tables and real-world waste tips, see our guide on how much concrete you need for sonotubes.

Concrete bag yield quick guide

Use this table to compare bag count and labor before you buy. Actual yield varies slightly by water ratio and site temperature.

Mix size Approx. yield per bag Typical 2026 price Best use case
60 lb concrete mix~0.45 cu ft$5.00 to $7.50Small repairs and 1 to 3 footings
80 lb concrete mix~0.60 cu ft$6.50 to $9.00Most DIY footing projects
Ready-mix deliverySold by cubic yard$170 to $220 per yardLarger pours, tighter schedule, consistency

Assumptions and limitations

This Sonotube calculator assumes the tube is a perfect cylinder with uniform inside diameter and depth. Real forms sometimes flare slightly at the bottom or compress in soft soil, which can change actual volume by 2% to 5%.

Bag yields (0.60 cu ft per 80 lb bag and 0.45 cu ft per 60 lb bag) are based on manufacturer specs at standard water ratios. Mixing too wet reduces yield and weakens the pour.

Common Sonotube calculator mistakes

The first mistake is using the wrong tube diameter from a rough estimate instead of the product label.

The second mistake is missing frost depth. In many US regions, footings must extend below frost line, often 36 to 48 inches, and shallow holes can fail inspection.

The third mistake is ordering no extra mix. Even careful pours lose concrete to spill, over-excavation, and uneven cuts, so a 5% to 10% waste buffer is usually cheaper than a last-minute material run.

Frequently Asked Questions

How do you calculate concrete for a Sonotube?

Use the cylinder volume formula: π × radius² × depth, with all measurements in feet. Convert tube diameter and depth from inches to feet first, calculate volume per tube, multiply by the number of tubes, then divide by 27 to convert cubic feet to cubic yards. Add 5 to 10 percent waste so your crew doesn't run short mid-pour. For a 12 in diameter (1 ft radius = 0.5 ft) × 48 in deep (4 ft) tube, volume per tube = π × 0.5² × 4 = 3.14 cubic feet. Worked example: four 12 in × 48 in deep tubes (a typical deck footing layout) need 4 × 3.14 = 12.57 cubic feet or 0.47 cubic yards, plus 10 percent waste = 0.51 cubic yards. At 2026 prices that's about 13 bags of 80 lb mix or a $145 to $260 small ready-mix delivery. Common mistake: using diameter as radius — always divide by 2 first.

How many bags of concrete does a 12 inch Sonotube need?

A 12 in diameter Sonotube at 48 in deep needs about 3.14 cubic feet of concrete before waste — that's roughly 6 bags of 80 lb mix (each bag yields 0.6 cubic feet) or 7 bags of 60 lb mix (each yields 0.45 cubic feet). With 10 percent waste factored in, plan on 6 to 7 bags of 80 lb mix per 12 in × 48 in tube. At 2026 prices of $5 to $7 per 80 lb bag, that's $30 to $50 in concrete per footing. Worked example: a 6-tube deck footing layout (12 in × 48 in each) needs 36 to 42 bags of 80 lb mix — $180 to $295 total. Common mistake: switching to 60 lb bags 'because they're easier to lift' — you'll need 33 percent more bags by count and pay more per cubic foot delivered. The 80 lb format almost always costs less per yard.

How many bags of concrete does an 8 inch Sonotube need?

An 8 in diameter Sonotube at 48 in deep needs about 1.40 cubic feet of concrete before waste — typically 3 bags of 80 lb mix or 4 bags of 60 lb mix. With 10 percent waste, round up to 3 to 4 bags of 80 lb per footing. At 2026 prices that's $15 to $30 per tube in concrete. Worked example: a 4-tube fence-post layout (8 in × 48 in each) needs 12 to 16 bags of 80 lb mix — $60 to $120 total. The 8 in tube is the smallest commonly used for fence posts and deck-railing footings; anything below 8 in tends to crack from frost heave. Common mistake: not adjusting tube depth for frost line — an 8 in tube only 24 in deep in a northern climate will heave and crack the post within two winters. Always set footings below the local frost depth (24 to 60 in depending on region).

How do you calculate Sonotube volume?

Measure tube diameter and depth in inches, convert both to feet (divide by 12), then apply the cylinder volume formula: V = π × r² × h. The radius is half the diameter. For a 10 in diameter × 36 in deep tube: radius = 5 in = 0.417 ft, depth = 36 in = 3 ft, volume = π × 0.417² × 3 = 1.64 cubic feet per tube. Multiply by tube count and divide by 27 for cubic yards. Worked example: eight 10 in × 36 in tubes need 8 × 1.64 = 13.1 cubic feet or 0.49 cubic yards, plus 10 percent waste rounds to 0.54 cubic yards (about 14 bags of 80 lb mix). Common mistake: forgetting to square the radius — using r instead of r² produces a result twice as big as the true volume and triples your concrete order, costing 2 to 3× more than necessary.

How many bags of concrete does an 18 inch Sonotube need?

An 18 in diameter Sonotube at 48 in deep holds about 7.07 cubic feet of concrete before waste — that's 12 bags of 80 lb mix or 16 bags of 60 lb mix per footing. With 10 percent waste, round up to 13 to 14 bags of 80 lb per tube. At 2026 prices that's $65 to $100 in concrete per footing. Worked example: a 4-tube structural deck-girder layout (18 in × 48 in each) needs 52 to 56 bags of 80 lb mix — $260 to $400 in concrete alone, plus the mixing time. At this volume most crews switch to small ready-mix delivery: a 1 cubic yard truck call runs $200 to $400 in 2026 and pours all 4 tubes in 15 minutes versus 2 to 3 hours of mixing. Common mistake: hand-mixing 50+ bags solo — by bag 30 the mix gets sloppy and consistency suffers.

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