Transparent method
How the Sonotube concrete calculator plans volume and cuts
The volume calculator's round branch takes diameter, height and quantity. This Sonotube concrete calculator adds product-line sizes, tube cut plans, a +1 in diameter check and two bag-rounding methods. The +1 in check never changes the order volume.
- 01
Pick the form line or measure it
Each product line limits the diameter and stock length lists. Other or measured form takes your own sizes.
- 02
Add the two height measurements
Measure form bottom to grade, then grade to top. For columns on footings or slabs, enter 0 below grade and full height above.
- 03
Read the cut plan before buying tubes
Short forms share tubes: stock length divided by form height, rounded down. Taller forms use full lengths first, then share tubes for the remainder.
- 04
Apply allowance before rounding bags
The Sonotube concrete calculator applies allowance to concrete only. Pooled bags round the total once; separate-form bags round each form, then multiply.
| Output | Formula |
|---|---|
| One form | π × (diameter ÷ 2)² × (height below grade + height above grade) |
| Order volume | one-form volume × form count × (1 + allowance ÷ 100) |
| Oversize check | π × ((nominal diameter + 1 in) ÷ 2)² × form height × form count |
| Stock tubes | ceiling(form count ÷ pieces per tube), pieces per tube = floor(stock length ÷ form height) |
Field context
Measure the full concrete height inside each form
Enter height below and above grade in the Sonotube concrete calculator. Measure stock tube length separately.
The image shows generic unbranded paper forms, not a manufacturer photo, logo or package. Forms called sono tubes or concrete tubes need the same two height measurements.
Check the arithmetic
Worked example: six 12 in forms, each 4 ft tall
At 0% allowance, one 12 in form 4 ft tall holds π × 0.5² × 4 = 3.141593 ft³ = 0.116355 yd³. Six forms hold 18.849556 ft³ = 0.698132 yd³ ≈ 0.534 m³, shown as 0.70 yd³.
At 13 in, one form holds 3.687008 ft³ and six hold 22.122048 ft³ (0.82 yd³), 17.4% more. That is a what-if check, not a claim that every 12 in form measures 13 in.
The QUIKRETE 80 lb record declares 0.60 ft³ per bag. Pooled, six forms need 31.4159 bags, rounded once to 32. Per form, 5.236 rounds to 6, so 6 × 6 = 36 bags.
Builder's Tube 4 ft stock needs one tube per form, six in all. Each 12 ft Round tube gives three 4 ft pieces, so two tubes cover six forms with 0 ft of offcut.
| Nominal diameter | ft³ per ft | ft³ per ft at +1 in | Added volume | Height per yd³ |
|---|---|---|---|---|
| 6 in | 0.196 | 0.267 | 36.1% | 137.51 ft |
| 8 in | 0.349 | 0.442 | 26.6% | 77.35 ft |
| 10 in | 0.545 | 0.660 | 21.0% | 49.50 ft |
| 12 in | 0.785 | 0.922 | 17.4% | 34.38 ft |
| 16 in | 1.396 | 1.576 | 12.9% | 19.34 ft |
| 24 in | 3.142 | 3.409 | 8.5% | 8.59 ft |
| 36 in | 7.069 | 7.467 | 5.6% | 3.82 ft |
| 48 in | 12.566 | 13.095 | 4.2% | 2.15 ft |
Use the result correctly
Three checks before using the quantities
01 Nominal size is not a measured inside diameter
Sonoco's FAQ says the inside diameter will be at least the stated size and can be up to 1 in larger. Outside diameter usually runs 1/2 to 1 in over the tube size, with up to 2 in possible. Builder's Tube literature calls for measuring when diameter is critical. Enter the inside diameter in measured mode.
02 Choose a bag count that matches allocation
Pooled rounding sums forms first. Separate-form rounding assigns whole bags per form for pours on different days.
03 Take structural dimensions from project information
Diameter, base size, reinforcement and capacity come from project drawings and a licensed engineer or architect, not this tool. Confirm pier depth with the local code inspector or a licensed structural engineer. Sonoco also states that the paper form is not load-bearing.
Sources and assumptions
Reference record
- Sonotube Frequently Asked Questions — nominal inside diameter, pour heights and splicing. Undated five-page PDF linked from the Sonotube product page; North America; checked .
- Sonotube Builder's Tube concrete forms brochure — Builder's Tube diameters, 4 ft length and above-ground limits. © 2016 Sonoco brochure, print code 16013/0716/1M; North America; checked .
- Sonotube Round concrete forms brochure — Round diameters from 6 to 36 in and the 12 ft standard length. © 2016 Sonoco brochure, print code 16013/0716/2M; North America; checked .
- Sonotube Commercial concrete forms brochure — Commercial diameters from 6 to 60 in with 12 and 20 ft lengths. © 2016 Sonoco brochure, print code 16013/0716/2M; North America; checked .
- Sonoco Legal — website operator and trademark notice. Current legal notice page, © 2026 Sonoco Products Company; Global website; checked .
- QUIKRETE Concrete Mix No. 1101 data sheet — declared U.S. yields for the QUIKRETE bag records. Concrete Mix No. 1101 data sheet, revised October 2022; US; checked .
- SAKRETE High-Strength Concrete Mix product page — declared U.S. yields for the SAKRETE bag records. U.S. product page, Product Details; US; checked .
- SAKRETE published product guide — item numbers for the SAKRETE bag records. SAKRETE Product Guide, 2021; US; checked .
- NIST Handbook 44, Appendix C — U.S. and metric volume conversions. NIST Handbook 44—2026, Appendix C; US; checked .
Sonotube data were checked September 27, 2026 for North America. Only 4 ft Builder's Tube stock is listed because Sonoco documents differ on longer lengths. We calculate the per-foot table.
Questions before ordering
Sonotube Concrete Calculator FAQ
How many bags of concrete does a 12 in Sonotube need?
For a 4 ft form at 0% allowance, the QUIKRETE 80 lb record (0.60 ft³) gives 5.236 bags, so 6 per form. Six forms need 32 bags rounded once or 36 rounded per form. Other bag records change the count.
Is a 12 inch Sonotube exactly 12 inches inside?
No. Sonoco calls its diameters nominal: the inside is at least the stated size and up to 1 in larger. Enter your measurement in Other or measured form.
How many forms can I cut from one stock tube?
A 12 ft tube gives three 4 ft pieces or two 5 ft pieces. The plan excludes saw kerf, damaged ends and splice collars.
What sizes do Sonotube forms come in?
In this tool, Builder's Tube covers 6, 8, 10 and 12 in with 4 ft stock. Round covers 6 to 36 in with 12 ft stock. Commercial covers 6 to 60 in with 12 and 20 ft stock. Store inventory varies.
Is this an official Sonotube calculator?
No. This Sonotube concrete calculator is independent and unaffiliated with Sonoco Products Company or SPC Resources, Inc.
Planning boundary
What this result does not decide
This Sonotube concrete calculator does not set diameter, depth, reinforcement or capacity. It skips enlarged bases, and product-line notes do not approve formwork.
Independent third-party calculator. Sonotube, Builder's Tube and RainGuard are Sonoco trademarks used here only to identify the referenced concrete forms and public product data. This site is not sponsored, endorsed by or affiliated with Sonoco Products Company or SPC Resources, Inc.