Sonotube Calculator
Estimate concrete, bag counts, form-tube length, and stock-tube cuts from a known diameter, fill height, and quantity.
Input convenience only. Verify the actual inside diameter and supplier availability.
How to measureDiameter + fill height
Measure the inside diameter across the round form and only the height that will actually contain concrete. Required structural dimensions come from the approved design or local authority.
Compare bag sizes or custom yield80 lb · 0.60 ft³/bag
Use the mixed yield printed on the product label.
Plan form-tube purchases and cutsNot configured
Embedded post or central voidNo deduction
Add material pricingNo price
Supply-only comparison. Bag cost and ready-mix cost are shown separately when both prices are entered; they are not added as though you would buy both concrete methods.
How to Use
- Choose a unit system - US mode uses inches for diameter and feet for height; metric mode uses centimetres and metres.
- Enter the inside diameter - use the actual round form size or measured inside diameter, not a recommended structural size.
- Enter the concrete fill height - measure only the height that will contain concrete.
- Enter the tube count and waste - all tubes in one run must have the same diameter and fill height.
- Refine only when needed - open bag settings, the cut planner, embedded-post deduction, or material pricing after the core estimate.
A 12 inch inside-diameter form filled 4 feet high contains about 3.14 cubic feet of concrete. With a 10 percent allowance, that is about 0.128 cubic yards or 6 bags when each bag yields 0.60 cubic feet. Enter the actual form diameter, concrete fill height, and number of identical tubes above. The calculator also totals form length and can plan cuts from the stock lengths available from your supplier.
Measure the Form, Then Plan the Cuts
What This Sonotube Calculator Estimates
The calculator uses the true cylinder formula for each round form, multiplies by the number of identical tubes, subtracts an optional embedded post or central void, and then applies the waste allowance. Results include concrete per tube, project volume, cubic yards, cubic metres, litres, and product-yield-based bag counts.
The specialist form-tube layer is what separates this page from a general pier calculator. It totals the linear form length and, when you open the cut planner, converts identical required sections into stock tubes, cutting patterns, and offcuts. Stock lengths and availability vary, so enter the lengths your supplier actually sells.
Concrete per Foot of Round Form
| Inside diameter | Concrete per vertical foot | 4 ft form with 10% allowance | 80 lb bags for 4 ft |
|---|---|---|---|
| 6 in | 0.196 ft³ | 0.032 yd³ | 2 bags |
| 8 in | 0.349 ft³ | 0.057 yd³ | 3 bags |
| 10 in | 0.545 ft³ | 0.089 yd³ | 4 bags |
| 12 in | 0.785 ft³ | 0.128 yd³ | 6 bags |
| 14 in | 1.069 ft³ | 0.174 yd³ | 8 bags |
| 16 in | 1.396 ft³ | 0.228 yd³ | 11 bags |
| 18 in | 1.767 ft³ | 0.288 yd³ | 13 bags |
| 24 in | 3.142 ft³ | 0.512 yd³ | 24 bags |
Bag counts assume 0.60 ft³ mixed yield per bag and round upward. Verify the yield printed on the actual product. Diameter and stock-length availability vary by Sonotube product line and local supplier.
Sonotube Concrete and Cut Formulas
The calculator keeps geometric volume, purchase rounding, and stock-tube planning as separate steps:
Net concrete per tube = gross tube volume − optional embedded post or void volume
Project before waste = net concrete per tube × number of identical tubes
Concrete to order = project volume × (1 + waste percentage)
Bag count = concrete to order ÷ mixed yield per bag, rounded up
Stock tubes to buy = required identical cuts ÷ cuts available per stock tube, rounded up
The calculator normalizes all units before applying the formulas, so equivalent imperial and metric dimensions return the same physical volume.
Bag Yields, Embedded Posts, and Form-Tube Cuts
Nominal bag weight is not the calculation by itself; mixed yield is. The presets use common planning yields, while the custom option lets the package label govern the estimate. Bag quantities round upward because partial bags are not an order quantity. For larger totals, compare handling and placement logistics with a ready-mix supplier rather than relying on one universal bag-versus-truck cutoff.
Leave the embedded-post deduction off for solid concrete piers. Open it only when a round, square, or rectangular post or void actually occupies part of the concrete volume. Reinforcement displacement is intentionally excluded; reinforcement comes from the approved design, and the existing rebar calculator remains the separate material takeoff tool.
The cut planner assumes identical required sections. Add a cut allowance when each section needs extra length for trimming or field adjustment. Reuse offcuts only when they are long enough, undamaged, permitted by the form manufacturer, and suitable for the approved pour sequence.
Quantity Estimate, Not Structural Design
- Enter the form diameter, concrete fill height, and reinforcement details specified by the approved plans or local building authority. Post size alone does not determine the required tube diameter. This calculator does not determine load capacity, soil bearing, frost depth, pier spacing, required embedment, or reinforcement.Sonoco Sonotube commercial forms and Builder’s Tube product information
- Published concrete-mix yields are planning values. Verify the yield, water requirement, placement instructions, and limitations printed on the product used for the project.QUIKRETE Concrete Mix product data
Next Steps
Volume figured, line up the pour and the posts:
Related Calculators
Sonotubes are the fastest way to form round footings. See the full construction calculator collection.
Frequently Asked Questions
How much concrete is in a 12 inch Sonotube?
A 12 inch inside-diameter form filled 4 feet high contains about 3.14 cubic feet, or 0.116 cubic yards, before waste. With a 10 percent allowance the order becomes about 0.128 cubic yards. At 0.60 cubic feet of mixed yield per bag, that is 6 bags after rounding up.
How many bags of concrete do I need per Sonotube?
Divide the concrete volume per tube, including the chosen allowance, by the mixed yield printed on the bag and round upward. The calculator provides 40, 50, 60, and 80 pound planning presets plus a custom-yield option so the product label can control the order.
How do I choose the correct Sonotube diameter?
Use the diameter specified by the approved structural plan or local building authority. Post dimensions alone do not determine the required form diameter because loads, soil, frost requirements, spacing, reinforcement, and jurisdiction all matter. The diameter presets are input conveniences, not structural recommendations.
Can the calculator plan cuts from 4, 8, or 12 foot tubes?
Yes. Open the stock-tube cut planner, enter the stock length available from your supplier, the required cut length, and any allowance per section. The result reports stock tubes to buy, a suggested identical-cut pattern, and offcut length. Availability varies by product line and supplier.
Should I subtract the volume of a wood or steel post?
Only when a post or central void actually occupies meaningful volume inside the form. Solid concrete piers should use no deduction. The optional deduction supports round and rectangular posts and can use a partial embedded height.
Is Sonotube a generic name?
Sonotube is a Sonoco concrete-form product family. Similar round fibre forms may be sold under other names. Verify the actual inside diameter, stock length, storage requirements, and placement instructions for the product being used.