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MaterialCalc — Sonotube Deck Footing Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

Sonotube Deck Footing Calculator

The tube size printed on the form — 8, 10, 12 or 16 inches.

How deep the concrete goes, not how long the tube is.

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Hand-dug holes are never as round as the tube.

Result

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Round tube footings are priced by volume, and volume grows with the square of the diameter — going from a 10 inch tube to a 12 inch tube adds 44% more concrete, not 20%. This calculator gives you the volume for your footing schedule, the bag count for each bag size, and what the concrete costs either way.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

Sonotube bell allowance
1

Plain tube with no flared base. A bell footing adds volume that this figure does not include.

Geometry — straight cylinder — Published product data, checked 09/01/2026

60 lb bag yield
0.45 ft³

Yield of one 60 lb bag of standard concrete mix.

Quikrete product data sheet — Published product data, checked 09/01/2026

80 lb bag yield
0.6 ft³

Yield of one 80 lb bag of standard concrete mix.

Quikrete product data sheet — Published product data, checked 09/01/2026

Ready-mix short-load threshold
1 yd³

Below roughly one cubic yard, most suppliers add a short-load fee that erases the price advantage over bags.

Regional ready-mix supplier schedules — Rough figure — widens the estimate range, checked 09/01/2026

Bags per pallet
42 bags

Above roughly one pallet of 80 lb bags, ready-mix is usually cheaper and always faster.

Home Depot / Lowe's pallet quantities — Industry standard, varies by supplier, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Volume of one footing = π × (diameter ÷ 2)² × pour depth. Multiply by the number of footings, add the waste allowance, then divide by the bag yield to get bag count. Bag counts always round up, because a partial bag is a full bag at the register.

Worked examples

Six 12 in footings, 42 in deep — a typical deck

Tube diameter: 12 Pour depth: 42 Number of footings: 6 Waste: 10

This lands just under a cubic yard, which is the awkward zone: too much to mix comfortably by hand, too little to order ready-mix without paying a short-load fee. Most builders bag this one.

Four 10 in footings, 4 ft deep — a cold-climate deck

Tube diameter: 10 Pour depth: 4' Number of footings: 4 Waste: 10

Deeper footings for a northern frost line, but the smaller diameter keeps the total down. Two inches less diameter saves about a third of the concrete at the same depth.

Twenty 16 in footings, 5 ft deep — a pole barn

Tube diameter: 16 Pour depth: 5' Number of footings: 20 Waste: 10

Well over a pallet of bags. Order ready-mix, and have the truck placed so the chute reaches as many holes as possible — pumping or wheelbarrowing is where the labor cost on this job lives.

Choosing materials

  • Measure pour depth, not tube length. Tubes are sold in 4 ft and 12 ft lengths and get cut down; if you order concrete for the tube instead of the hole, you will over-order on every footing.
  • A bell or flared base holds meaningfully more concrete than a straight tube. This calculator assumes a straight cylinder, so add the bell volume separately if your footings are belled.
  • Under about a cubic yard, bagged concrete usually beats ready-mix once the short-load fee is counted. Above a pallet of bags — roughly 42 of the 80 lb size — ready-mix is both cheaper and enormously faster.
  • 80 lb bags cost less per cubic foot than 60 lb bags but weigh 80 pounds each. If you are working alone, or lifting over a trench, the 60 lb bag is often worth the premium.
  • Footings bear below the frost line, and the required depth is set locally. Check with your building department before you dig; a footing at the wrong depth is a footing you pour twice.

Common questions

How much concrete does a 12 inch Sonotube take per foot of depth?

A 12 inch tube holds about 0.79 cubic feet per foot of depth, so a 4 ft pour is roughly 3.1 cubic feet — about five 80 lb bags. A 10 inch tube holds about 0.55 cubic feet per foot, and an 8 inch tube about 0.35.

Should I measure the tube or the hole?

Measure the pour depth — how deep the concrete actually goes. Tubes are cut to fit and the offcut is waste, so ordering against tube length over-orders on every footing. If the hole is wider than the tube at the bottom, that extra volume is what the waste allowance covers.

Do I need gravel under a Sonotube footing?

It depends on your jurisdiction. Some codes require a compacted gravel base for drainage; others have the tube bear directly on undisturbed soil. Check locally before you dig, because it changes both your hole depth and your material list.

Is it cheaper to use bags or order ready-mix?

Under roughly one cubic yard, bags are almost always cheaper because ready-mix suppliers add a short-load fee that can exceed the concrete itself. Above a pallet of bags, ready-mix wins on both price and time. The compare table on this page prices both against your own numbers.

Why does the estimate show a range instead of one price?

Because some inputs are firmer than others. Bag prices are shelf prices and are reliable; short-load fees and excavation labor vary widely by supplier and region. The range widens when a low-confidence input is involved, and the result card names which one.

How much waste should I allow on footings?

Ten percent is the usual allowance and the default here. Hand-dug holes justify more — they are never as round as the tube, and the space between the tube and the earth has to be backfilled or filled. Machine-augured holes in stable soil can run closer to 5%.

Does this include the concrete for a bell or flared base?

No. The calculation is a straight cylinder. A belled base can add 30% or more to a single footing, so if your drawings call for one, calculate the bell separately and add it.

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