Sonotube Calculator
A sonotube calculator turns tube diameter, depth and count into cubic feet, bags and tubes to buy. One 12 inch tube filled 4 feet high holds 3.14 cubic feet. Eight of them need 27.65 cubic feet with 10 percent waste, which is 47 bags of 80 lb concrete.
This tool is part of our project calculators. Use it to order concrete and tube for deck, porch and fence footings. Your building department sets the size and depth.
- Updated October 2026
- Sources Cited
- No Login Required
- Free to Use
Your concrete
Buy this many bags
47 bags of 80 lb
27.65 cu ft with 10% waste, which is 1.02 cu yd (0.78 cu m)
- Concrete height per tube
- 48 in
- One tube holds
- 3.14 cu ft
- Per foot of tube
- 0.785 cu ft
- All tubes, no waste
- 25.13 cu ft
- Bags per tube, rounded up
- 6
- Bags if each tube is rounded
- 48
Bags by size
| Bag | Yield | Bags |
|---|---|---|
| 40 lb | 0.3 cu ft | 93 |
| 50 lb | 0.375 cu ft | 74 |
| 60 lb | 0.45 cu ft | 62 |
| 80 lb | 0.6 cu ft | 47 |
| 90 lb | 0.675 cu ft | 41 |
Tubes to buy
| Stock | Per stock tube | Buy | Left over |
|---|---|---|---|
| 4 ft | 1 | 8 | 0 ft |
| 8 ft | 2 | 4 | 0 ft |
| 12 ft | 3 | 3 | 4 ft |
Each tube is cut to 4 ft. A tube longer than the stock length is not listed.
Five bag sizes
40, 50, 60, 80 and 90 lb bags, using the yields printed on the bag.
Stock tube plan
4, 8 and 12 foot tubes, with the cut pieces and what is left.
Per tube or pooled
See the count for one tube and for the whole job.
Estimates are for ordering. Holes are rarely perfect, so keep the waste allowance. Prices are never built in. You type them.
How to calculate concrete for a Sonotube
A tube is a cylinder. Cubic feet equal 3.1416 x (diameter in inches / 24) squared x height in feet. A 12 inch tube holds 0.785 cubic feet per foot of height. Filled 4 feet high it holds 3.14. Divide by the bag yield and round up to get bags.
- Pick the tube diameter. Measure the inside diameter if you use a custom size.
- Add the depth below grade to the height above grade. That is the fill height.
- Multiply the circle area by the fill height to get cubic feet for one tube.
- Multiply by the tube count, then by one plus the waste.
- Divide by the bag yield and round up. An 80 lb bag yields 0.60 cubic feet.
For a slab or a wide footing, use our concrete calculator. For bag counts on any shape, use the concrete bag calculator.
Worked example: eight 12 inch footing tubes
A deck has eight posts. Each tube is 12 inches wide, goes 42 inches below grade and stands 6 inches above. Fill height is 48 inches, or 4 feet. One tube holds 3.14 cubic feet. Eight hold 25.13. With 10 percent waste the order is 27.65 cubic feet, or 1.02 cubic yards.
| Step | Working | Result |
|---|---|---|
| Fill height | 42 + 6 in | 48 in = 4 ft |
| One tube | 3.1416 x 0.5 x 0.5 x 4 | 3.14 cu ft |
| Eight tubes | 3.14 x 8 | 25.13 cu ft |
| Waste, 10% | 25.13 x 1.10 | 27.65 cu ft |
| Cubic yards | 27.65 / 27 | 1.02 cu yd |
| Bags of 80 lb | 27.65 / 0.60, rounded up | 47 bags |
Check the post count against your deck plan with our deck calculator.
Concrete per foot by tube diameter
Volume grows with the square of the diameter. A 12 inch tube holds 0.785 cubic feet per foot. A 24 inch tube holds 3.142, four times as much. Multiply the figure in the table by your fill height in feet.
| Diameter | Cu ft per foot, computed | Sonoco published |
|---|---|---|
| 6 in | 0.196 | 0.20 |
| 8 in | 0.349 | 0.35 |
| 10 in | 0.545 | 0.55 |
| 12 in | 0.785 | 0.80 |
| 14 in | 1.069 | Not listed |
| 16 in | 1.396 | Not listed |
| 18 in | 1.767 | Not listed |
| 24 in | 3.142 | Not listed |
| 30 in | 4.909 | Not listed |
| 36 in | 7.069 | Not listed |
Sonoco rounds its figures to two decimals, so its 6 inch value is 0.20 where the exact value is 0.196.
Bags per tube, checked against QUIKRETE
The table gives bags to fill one tube with no waste, rounded up. A 12 inch tube filled 4 feet high takes 6 bags of 80 lb or 7 bags of 60 lb. An 8 inch tube filled 4 feet takes 3 bags of 80 lb or 4 of 60 lb.
| 80 lb bags | 1 ft | 2 ft | 3 ft | 4 ft |
|---|---|---|---|---|
| 6 in tube | 1 | 1 | 1 | 2 |
| 8 in tube | 1 | 2 | 2 | 3 |
| 10 in tube | 1 | 2 | 3 | 4 |
| 12 in tube | 2 | 3 | 4 | 6 |
| 60 lb bags | 1 ft | 2 ft | 3 ft | 4 ft |
|---|---|---|---|---|
| 6 in tube | 1 | 1 | 2 | 2 |
| 8 in tube | 1 | 2 | 3 | 4 |
| 10 in tube | 2 | 3 | 4 | 5 |
| 12 in tube | 2 | 4 | 6 | 7 |
These counts follow the yields printed on the bag: 0.45 cubic feet for 60 lb and 0.60 for 80 lb. Read the bag you buy, since yields differ by brand and mix.
How deep to dig and how long to cut the tube
The footing bottom must sit 12 inches below undisturbed grade and below the local frost line, whichever is deeper, per IRC R403.1.4 as cited by the Home Depot footing guide. Cut the tube to the depth below grade plus the height you want above grade. Your local code decides the final number.
| Region | Approximate frost depth |
|---|---|
| Northern New England and the Dakotas | 60 inches or more |
| Upper Midwest | 42 to 48 inches |
| Mid-Atlantic | 24 to 26 inches |
| Gulf South | 0 inches |
These depths are approximate. Ask your building department for the frost depth at your address. For fence posts, see our fence calculator.
Stock tubes: 4, 8 or 12 foot
Sonoco sells Builder's Tube in stock lengths of 4, 8 and 12 feet, cut to fit. Eight tubes of 4 feet need 8 four-foot tubes, 4 eight-foot tubes or 3 twelve-foot tubes. The longer sizes leave scrap, so compare the leftover before you buy.
| Stock length | Pieces per stock tube | Stock tubes to buy | Leftover |
|---|---|---|---|
| 4 ft | 1 | 8 | 0 ft |
| 8 ft | 2 | 4 | 0 ft |
| 12 ft | 3 | 3 | 4 ft |
Round per tube or round the total
Rounding one tube up and multiplying gives 48 bags. Pooling all the concrete and rounding once gives 47. Pooled is the better order when you mix bags from one pile. Per tube suits a job where each footing is poured as its own batch with no leftover carried over.
The calculator shows both counts so you can pick. Bags left over from one pour can go into the next tube only if the mix is still workable.
Sonotube calculator or concrete calculator
Use this page for round tubes. It adds tube diameter, depth below grade, stock lengths and a per-tube bag count. Use the concrete calculator for slabs, walls and square footings. The cylinder math is the same, but the inputs and outputs differ.
For a block wall base, see the retaining wall calculator. For steel in a footing, use the rebar calculator.
What this calculator does not cover
It does not size a footing. Load, soil and code set the diameter and depth. It does not include rebar, anchors, bolts, bell footings or the soil removed from the hole. It uses only the price you type. Ask your building department or a deck designer before you dig, and consult your supplier on bag yield.
Methodology and sources
Published October 2026. Last updated October 2026. Next review October 2027.
Reviews: volume calculators · 38 calculators reviewed
Alex Rivera is a Licensed Professional Engineer (PE) with 18 years of structural and civil engineering experience. He holds PE licenses in California (#C-89412) and Texas (#P.E.-98765). He previously served as Engineer of Record on 250+ residential foundation designs at Thornton Tomasetti. At CalcSummit, he writes and personally reviews every structural, concrete, rebar, deck, and framing calculator against current IRC and ACI 318 standards.
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