Concrete Tube Calculator: Sonotube Volume, Bags and Cost
A cardboard tube is cheap. Overfilling it and having concrete left over is not. This concrete tube calculator works out the volume one tube holds, multiplies it by how many you’re pouring, and returns weight, bag count, and cost for either a full or partial fill. Enter the tube diameter and depth, set the count, and the numbers update as you type.
Use it for deck piers, fence post footings, mailbox bases, and anything built with a Sonotube or similar form. Two fill options are covered. Full fill assumes solid concrete through the whole tube. Partial fill assumes about half the cross-section, which is what happens when a pier has a void or only the structural center gets grouted.
How to Use the Concrete Tube Calculator
Choose your currency from the top dropdown.
Enter the tube diameter. Twelve inches is the common default.
Set the depth or height of the pour inside the tube.
Pick units for each: in, cm, mm, ft, or m.
Enter how many tubes you’re pouring.
Choose full fill or partial fill.
Adjust waste, then set concrete strength, density, and bag size.
Add your price per bag and price per cubic yard.
The Summary tab shows volume per tube first, then total volume, weight, bags, and both cost paths. Detailed Breakdown lists every intermediate value.
How the Concrete Tube Calculator Formula Works
Every tube is a cylinder. Cross-section area comes from the radius, volume comes from area times height, and the fill type scales the result.
Formula: Cross-section = π × (Diameter ÷ 2)²
Formula: Volume per tube = Cross-section × Height × Fill factor
Formula: Total volume with waste = Volume per tube × Count × (1 + Waste %)
Formula: Bags = ⌈ Total volume with waste ÷ (Bag size in lb ÷ 133) ⌉
The fill factor is 1.0 for full fill and 0.5 for partial. That half factor is an estimate, not a precise void ratio. If a tube is filled only to the top of a rebar cage and left hollow below, the real fraction is somewhere near half. Most deck piers end up in that zone.
The 133 constant is pounds of mixed concrete per cubic foot. That’s why an 80 lb bag yields about 0.60 ft³. A 60 lb bag yields about 0.45 ft³, and a 40 lb bag yields roughly 0.30 ft³.
Ready-mix runs on volume only.
Formula: Ready-mix cost = Total volume with waste (yd³) × Price per yd³
If you enter price per cubic meter, the tool converts by multiplying by 0.764555 before the total runs. Strength records your PSI target in the breakdown but doesn’t shift the bag yield.
The recommendation is a simple threshold. Above 1 cubic yard, ready-mix gets the nod. At or below, bags win. Validation is minimal: if diameter or height is zero, the results clear. No upper bound exists.
Worked Example: Eight Deck Piers in 10 in Tubes
Say you’re pouring eight pier footings for a deck. Each uses a 10-inch Sonotube, poured 3.5 ft deep. Full fill. Waste factor is 10%. Bag size is 80 lb. Price is $6.50 per bag, ready-mix is $150 per cubic yard.
Diameter in feet: 10 ÷ 12 = 0.8333 ft
Radius: 0.4167 ft
Cross-section: π × 0.4167² = 0.5454 ft²
Volume per tube: 0.5454 × 3.5 = 1.909 ft³
Total volume: 1.909 × 8 = 15.27 ft³, or 0.566 yd³
With 10% waste: 16.80 ft³, or 0.622 yd³
Concrete weight: 16.80 × 145 = 2,436 lbs (about 1,105 kg)
Yield per 80 lb bag: 80 ÷ 133 = 0.6015 ft³
Bags needed: 16.80 ÷ 0.6015 = 27.9, rounded to 28
Cost using bags: 28 × $6.50 = $182.00
Cost using ready-mix: 0.622 × $150 = $93.30
Recommended method: Bagged Concrete
The total stays under one cubic yard, so bags come out ahead on price by about $89. The truck would also charge a short-load fee at this volume, which pushes the gap wider. Mixing 28 bags on a Saturday is a real day’s work, but it’s the cheaper path.
