Enter measured form dimensions
Concrete form-tube bag calculator
This purpose-specific interface delegates every calculation, allowance, validation, warning, product yield, and whole-bag rounding step to the existing tested post-hole concrete engine in round-hole/no-post mode.
Your quantity estimate
- Raw per tube
- Raw total
- With allowance
- Whole-bag order
Concrete form-tube bag table by actual inside diameter
Raw whole bags and whole bags with a 10% example allowance are calculated independently. Quantity is one tube per row.
| Measured tube and raw volume | Raw whole bags | Whole bags with 10% allowance | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Inside diameter | Filled height | Raw ft³ | Raw yd³ | 40 lb | 60 lb | 80 lb | 40 lb | 60 lb | 80 lb |
| 8 in | 24 in | 0.70 | 0.026 | 3 | 2 | 2 | 3 | 2 | 2 |
| 8 in | 36 in | 1.05 | 0.039 | 4 | 3 | 2 | 4 | 3 | 2 |
| 8 in | 48 in | 1.40 | 0.052 | 5 | 4 | 3 | 6 | 4 | 3 |
| 10 in | 24 in | 1.09 | 0.040 | 4 | 3 | 2 | 4 | 3 | 2 |
| 10 in | 36 in | 1.64 | 0.061 | 6 | 4 | 3 | 6 | 4 | 3 |
| 10 in | 48 in | 2.18 | 0.081 | 8 | 5 | 4 | 8 | 6 | 4 |
| 12 in | 24 in | 1.57 | 0.058 | 6 | 4 | 3 | 6 | 4 | 3 |
| 12 in | 36 in | 2.36 | 0.087 | 8 | 6 | 4 | 9 | 6 | 5 |
| 12 in | 48 in | 3.14 | 0.116 | 11 | 7 | 6 | 12 | 8 | 6 |
| 14 in | 24 in | 2.14 | 0.079 | 8 | 5 | 4 | 8 | 6 | 4 |
| 14 in | 36 in | 3.21 | 0.119 | 11 | 8 | 6 | 12 | 8 | 6 |
| 14 in | 48 in | 4.28 | 0.158 | 15 | 10 | 8 | 16 | 11 | 8 |
| 16 in | 24 in | 2.79 | 0.103 | 10 | 7 | 5 | 11 | 7 | 6 |
| 16 in | 36 in | 4.19 | 0.155 | 14 | 10 | 7 | 16 | 11 | 8 |
| 16 in | 48 in | 5.59 | 0.207 | 19 | 13 | 10 | 21 | 14 | 11 |
| 18 in | 24 in | 3.53 | 0.131 | 12 | 8 | 6 | 13 | 9 | 7 |
| 18 in | 36 in | 5.30 | 0.196 | 18 | 12 | 9 | 20 | 13 | 10 |
| 18 in | 48 in | 7.07 | 0.262 | 24 | 16 | 12 | 26 | 18 | 13 |
Concrete form-tube quantity questions
How many 80-lb bags fill a 12-in tube 48 in deep?
For one tube with a 12-in actual inside diameter and 48-in concrete-filled height, the engine calculates 3.14 ft³ raw and 3.46 ft³ with 10% allowance, rounding to 6 whole 80-lb bags at the verified 0.60-ft³ yield.
Should I use the tube’s nominal or actual inside diameter?
Use the actual usable inside diameter because the concrete cylinder is defined by that measurement. Check the current product data or measure the form.
Is tube length the same as concrete-filled depth?
Not necessarily. Enter the height actually filled with concrete. Overall tube length, excavation depth, and any unfilled portion are separate.
How do I calculate several identical tubes?
Enter the quantity. The engine combines raw cylinder volume, applies the selected allowance once, and then rounds the project to whole bags.
Why do 60- and 80-lb bag counts depend on the product yield?
Bag weight does not itself define mixed concrete volume. This page uses the selected product’s verified published cubic-foot yield.
Should a post’s displacement be subtracted?
This form-tube interface intentionally uses no-post mode. If a post occupies the concrete, use the Post Hole Concrete Calculator so its actual displacement can be represented.
Does this calculator determine footing diameter or frost depth?
No. Diameter, depth, bearing, reinforcement, and frost requirements are structural and local decisions outside this quantity calculation.
Sources and calculation basis
- QUIKRETE Concrete Mix Data Sheet 1101 — verified 40/60/80-lb yields.
- JobsiteMeasure methodology and source register — cylinder geometry, allowance, and whole-bag-rounding basis.
Values generated September 3, 2026.