This Sonotube concrete calculator gives the cubic yards, cubic feet and 40, 60 or 80 lb bags needed to fill round column forms. A Sonotube is a cylinder, so each tube holds π × (diameter ÷ 2)² × height. A 12 inch tube 4 feet deep holds 3.14 ft³, which is 6 bags of 80 lb mix. Enter your tube diameter, depth and number of tubes. You can add a flared footing or Tube Base, subtract the post if it is set in the concrete, and include a waste allowance to get a total you can take to the store.
Bag yields come from the manufacturers' own data sheets. Quikrete Concrete Mix and Sakrete High Strength Concrete Mix both list 0.30 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag and 0.60 ft³ for an 80 lb bag. Tube Base volumes come from Sonoco's brochure. The calculator rounds the bag count up, because you can't buy a partial bag.
How to use the Sonotube calculator
- Choose the tube diameter. Sonoco lists its Builder's Tube in 6, 8, 10 and 12 in diameters, and its standard Sonotube forms in larger sizes. For anything else, choose "Other" and enter the inside diameter you measured.
- Enter the depth as the full concrete height: the part below ground plus any part of the tube above grade.
- Enter the number of tubes that share the same size.
- Add a footing if there is one. Pick a Sonotube Tube Base, or choose "Round pad" and enter the diameter and thickness of a cast pad or bell.
- Subtract the post if you set a 4×4, 6×6 or 8×8 directly in wet concrete, and enter how deep it goes.
- Set a waste percentage. The default of 10% is our own planning assumption, not a code figure. Use less for small, carefully mixed jobs and more when hole sides are rough.
How to calculate concrete for a round column
The volume of a cylinder is V = π × r² × h. Measure the diameter in inches, halve it to get the radius, square it, multiply by π and by the height in inches, then divide by 1,728 to get cubic feet. NIST Handbook 44 fixes 1 ft³ at 1,728 in³ and 1 yd³ at 27 ft³. To get bags, divide the cubic feet by the bag yield and round up.
Example: a 10 in tube 42 in deep holds π × 5² × 42 = 3,299 in³. Divided by 1,728, that is 1.91 ft³, or 0.071 yd³. Divided by 0.60, it needs 4 bags of 80 lb mix.
Concrete per foot of Sonotube by diameter
To use this table, multiply the per-foot figure by your depth in feet. The bag columns show fractional bags per foot, so round the total up at the end rather than rounding each foot.
| Diameter | ft³ per ft | yd³ per ft | 80 lb bags per ft | 60 lb bags per ft | 40 lb bags per ft | 80 lb bags, 4 ft tube |
|---|---|---|---|---|---|---|
| 6 in | 0.196 | 0.0073 | 0.33 | 0.44 | 0.65 | 2 |
| 8 in | 0.349 | 0.0129 | 0.58 | 0.78 | 1.16 | 3 |
| 10 in | 0.545 | 0.0202 | 0.91 | 1.21 | 1.82 | 4 |
| 12 in | 0.785 | 0.0291 | 1.31 | 1.75 | 2.62 | 6 |
| 14 in | 1.069 | 0.0396 | 1.78 | 2.38 | 3.56 | 8 |
| 16 in | 1.396 | 0.0517 | 2.33 | 3.1 | 4.65 | 10 |
| 18 in | 1.767 | 0.0654 | 2.95 | 3.93 | 5.89 | 12 |
| 20 in | 2.182 | 0.0808 | 3.64 | 4.85 | 7.27 | 15 |
| 24 in | 3.142 | 0.1164 | 5.24 | 6.98 | 10.47 | 21 |
| 30 in | 4.909 | 0.1818 | 8.18 | 10.91 | 16.36 | 33 |
| 36 in | 7.069 | 0.2618 | 11.78 | 15.71 | 23.56 | 48 |
| 42 in | 9.621 | 0.3563 | 16.04 | 21.38 | 32.07 | 65 |
| 48 in | 12.566 | 0.4654 | 20.94 | 27.93 | 41.89 | 84 |
These figures match Sonoco's published chart for its Builder's Tube, which lists 0.20, 0.35, 0.55 and 0.80 ft³ per foot for 6, 8, 10 and 12 in tubes, rounded from the exact values above. Sonoco notes that its diameter sizes are nominal, so if accuracy is critical, measure the inside of your tube.
How many bags of concrete in a yard?
| Bag size | Yield per bag | Bags per yd³ | Bags per 10 ft³ |
|---|---|---|---|
| 40 lb | 0.3 ft³ | 90 | 34 |
| 60 lb | 0.45 ft³ | 60 | 23 |
| 80 lb | 0.6 ft³ | 45 | 17 |
Bags only make sense up to a point. Once a job reaches a yard or more, compare the cost and labor of mixing 45 bags of 80 lb mix with a ready-mix delivery or a towable mixer. That is why figuring yards of concrete matters even for a small deck: eight piers can add up quickly.
Flared footings, bells and Tube Bases
A straight tube only bears on the soil under its own circle. A flared base spreads the load over a larger area, which is why deck guides specify footing sizes by diameter. The American Wood Council's DCA 6 deck guide Table 4 lists round footing diameters from 18 to 42 in and thicknesses from 7 to 19 in, depending on beam and joist span. It assumes soil bearing of 1,500 psf and concrete weighing 150 pcf. Your design or your building department sets the actual size.
This calculator handles footings in two ways:
- Sonotube Tube Base: Sonoco lists the TB22 (2.0 ft³, fits 8 and 10 in tubes), the TB28 (4.5 ft³, fits 8, 10 and 12 in) and the TB32 (7.0 ft³, fits 12 to 18 in). The calculator adds that volume to each tube and warns you if the base doesn't fit your tube size.
- Round pad or bell: enter the pad diameter and thickness, and the calculator treats the pad as a short cylinder under the tube. For a cone-shaped bell, you can enter the average diameter as a close approximation.
| Pad diameter | 8 in thick | 10 in thick | 12 in thick | 80 lb bags at 10 in |
|---|---|---|---|---|
| 18 in | 1.18 ft³ | 1.47 ft³ | 1.77 ft³ | 3 |
| 20 in | 1.45 ft³ | 1.82 ft³ | 2.18 ft³ | 4 |
| 24 in | 2.09 ft³ | 2.62 ft³ | 3.14 ft³ | 5 |
| 27 in | 2.65 ft³ | 3.31 ft³ | 3.98 ft³ | 6 |
| 30 in | 3.27 ft³ | 4.09 ft³ | 4.91 ft³ | 7 |
| 36 in | 4.71 ft³ | 5.89 ft³ | 7.07 ft³ | 10 |
How deep should the tubes go?
DCA 6 follows IRC Section R403: all footings must bear on undisturbed soil at least 12 in below the undisturbed ground surface or below the frost line, whichever is deeper. The authority having jurisdiction sets the frost line. Deck footings closer than 5 ft to a house foundation wall must bear at the same elevation as the house footing. DCA 6 also says bearing conditions shall be verified in the field by the building official before concrete is placed. Get your local frost depth from the permit office before you buy tubes, because it usually decides the tube length.
Worked examples
Deck piers: eight 12 in tubes, 4 ft deep, 10% extra
Each tube holds 3.14 ft³, so eight tubes plus 10% come to 27.65 ft³, or 1.02 yd³. That is 47 bags of 80 lb mix or 62 bags of 60 lb mix.
10 in tube on a TB28 base with a 6×6 post set 42 in
The column holds 1.91 ft³ and the base adds 4.5 ft³. The post displaces 0.74 ft³, leaving 5.67 ft³ per hole, which is 10 bags of 80 lb mix. The base holds more concrete than the tube, which surprises many first-time builders.
12 in tube on a 24 × 10 in cast pad
The tube holds 3.14 ft³ and the pad adds 2.62 ft³, for a total of 5.76 ft³, or 10 bags of 80 lb mix.
Fence post: 8 in tube, 3 ft deep, 4×4 post set full depth
1.05 ft³ minus 0.26 ft³ for the post leaves 0.79 ft³, which is 2 bags of 80 lb mix or 3 bags of 40 lb mix.
Large column: 24 in form, 10 ft tall
π × 12² × 120 ÷ 1,728 = 31.42 ft³ = 1.16 yd³. That would take 53 bags of 80 lb mix, so a column this size is a ready-mix job.
Post sizes: nominal vs actual
Lumber is sold by nominal size. NIST's American Softwood Lumber Standard (PS 20) sets the minimum dressed dry sizes: a nominal 4 in dimension piece is 3½ in, a 6 in timber is 5½ in, and an 8 in timber is 7¼ in. Green (unseasoned) timbers can be slightly larger. The calculator subtracts the square of the actual size times the embedded depth. For a 4×4 in an 8 in tube, the post takes up about 24% of the tube's cross-section, enough to save one or two bags on a long run.
Common mistakes
- Using the nominal tube size when the tube is oversized or egg-shaped. Measure the inside diameter if precision matters, because Sonoco itself calls its sizes nominal.
- Forgetting the part above grade. A tube that sticks up 8 in to keep the post dry needs concrete for that height too.
- Leaving out the bell. A Tube Base or flared hole can hold more concrete than the tube above it.
- Rounding each foot of bags down. Add up the total volume first, then round up once.
- Mixing yields across products. The 0.60 ft³ figure applies to standard 80 lb concrete mix. Fast-setting, high-early and lightweight mixes can yield differently, so check the bag.
For slabs, paths and other flat pours, use the cubic yards calculator. For boxes and rectangular forms, use the cubic feet calculator. To lay out the anchor bolts that go on top of a round pier, use the bolt circle calculator.
Frequently asked questions
How many bags of concrete do I need for a Sonotube?
Multiply π × (diameter ÷ 2)² × height to get cubic inches, divide by 1,728 for cubic feet, and divide by the bag yield. A 12 in tube 4 ft deep holds 3.14 ft³, which is 6 bags of 80 lb mix (0.60 ft³ each), 7 bags of 60 lb or 11 bags of 40 lb.
How many 80 lb bags of concrete are in a yard?
A cubic yard is 27 ft³. Quikrete and Sakrete both list an 80 lb bag as yielding 0.60 ft³, so a yard takes 27 ÷ 0.60 = 45 bags. It takes 60 bags of 60 lb mix or 90 bags of 40 lb mix.
How much concrete is in an 8 inch Sonotube per foot?
An 8 in tube holds 0.349 ft³ per foot of height. Sonoco's chart rounds this to 0.35 ft³, or about ⅗ of an 80 lb bag per foot.
How much concrete does a 12 inch Sonotube take?
A 12 in tube holds π × 0.5² = 0.785 ft³ per foot, or 0.0291 yd³. A 4 ft tube holds 3.14 ft³, which is 6 bags of 80 lb mix.
How many Sonotubes does a yard of concrete fill?
Divide 27 ft³ by the volume of one tube. One yard fills 8.6 tubes that are 12 in × 4 ft, 12.4 tubes that are 10 in × 4 ft, or 19.3 tubes that are 8 in × 4 ft.
How deep should a Sonotube footing be?
The AWC DCA 6 deck guide, which is based on IRC Section R403, requires footings to bear on undisturbed soil at least 12 in below the undisturbed ground surface or below the frost line, whichever is deeper. Your local building department sets the frost depth.
Should I subtract the post from the concrete?
Only if the post is set in the wet concrete. A 6×6 is actually 5½ in square, so it displaces 5.5 × 5.5 = 30.25 in² for every inch it is embedded, about 0.21 ft³ per foot. If the post sits on a bracket on top of the pier, leave the post option at "No post".
How much does a Sonotube full of concrete weigh?
The AWC DCA 6 footing tables assume concrete at 150 lb/ft³. On that basis a 12 in × 4 ft pier weighs about 471 lb.
What is the formula for figuring yards of concrete in a round column?
Cubic yards = π × (diameter in ft ÷ 2)² × height in ft ÷ 27. Working in inches, it is π × (diameter ÷ 2)² × height ÷ 46,656, because there are 46,656 cubic inches in a cubic yard.
Does a bell or flared footing change the bag count much?
Yes. A Sonotube Tube Base TB28 adds 4.5 ft³ according to Sonoco, which is more than a 10 in × 42 in tube holds on its own (1.91 ft³). That can more than double the bags per hole, so include the footing in the estimate.
Sources & method
- NIST Handbook 44 (2026), Appendix C: 1 ft³ = 1,728 in³; 1 yd³ = 27 ft³
- QUIKRETE Concrete Mix No. 1101 product data sheet: 40 lb 0.30 ft³, 60 lb 0.45 ft³, 80 lb 0.60 ft³ yield
- SAKRETE High Strength Concrete Mix technical data sheet: 40 lb 0.30 ft³, 60 lb 0.45 ft³, 80 lb 0.60 ft³
- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide (2015 IRC), Footings [R403] and Table 4
- Sonoco, Sonotube Builder's Tube concrete forms: 6–12 in diameters, ft³ per foot of height
- Sonoco, Sonotube concrete forming products brochure: Tube Base TB22/TB28/TB32 fits and concrete volumes
- NIST Voluntary Product Standard PS 20-20 (Rev. 1, 2021), American Softwood Lumber Standard, Table 3: dressed sizes
Results are estimates for general information. Found an error? It helps everyone — see our methodology.