Sonotube & Form Tube Concrete Calculator
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- Imperial and metric
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Results
4 80 lb bags per tube, 24 in total
| Bag size | Yield per bag | Bags | Weight |
|---|---|---|---|
| 40 lb | 0.300 ft³ | 44 | 1,760 lb |
| 50 lb | 0.375 ft³ | 35 | 1,750 lb |
| 60 lb | 0.45 ft³ | 30 | 1,800 lb |
| 80 lb | 0.60 ft³ | 22 | 1,760 lb |
Concrete per foot of form tube
| Tube diameter | ft³ per foot | yd³ per foot | 80 lb bags for a 4 ft tube |
|---|---|---|---|
| 6 in | 0.196 | 0.007 | 2 |
| 8 in | 0.349 | 0.013 | 3 |
| 10 in | 0.545 | 0.02 | 4 |
| 12 in | 0.785 | 0.029 | 6 |
| 14 in | 1.069 | 0.04 | 8 |
| 16 in | 1.396 | 0.052 | 10 |
| 18 in | 1.767 | 0.065 | 12 |
| 20 in | 2.182 | 0.081 | 15 |
| 24 in | 3.142 | 0.116 | 21 |
| 30 in | 4.909 | 0.182 | 33 |
| 36 in | 7.069 | 0.262 | 48 |
| Tube diameter | Liters per meter |
|---|---|
| 150 mm | 17.7 L |
| 200 mm | 31.4 L |
| 250 mm | 49.1 L |
| 300 mm | 70.7 L |
| 400 mm | 125.7 L |
| 450 mm | 159 L |
| 600 mm | 282.7 L |
How the calculation works
Bell volume = π × h ÷ 3 × (r₁² + r₁·r₂ + r₂²), where r₁ is the tube radius and r₂ the bell's bottom radius
Six 10-inch tubes 4 feet tall hold 2.18 ft³ each, 13.09 ft³ in all (0.48 yd³). Adding a 20-inch bell footing, 12 inches tall, under each one adds 1.27 ft³ per tube, for a total of 20.73 ft³, or about 35 bags of 80 lb concrete.
Choosing a tube size
The tube carries the post load down to a footing, so the right size depends on how much load each post carries and on your soil. Deck and porch plans, or your local building code, set the footing size; in the US the deck provisions of the International Residential Code are the usual reference. Many residential decks use 8 to 12 inch tubes, often on a wider footing pad or a plastic bell base that spreads the load.
Tips for pouring form tubes
- Brace the tube. Wet concrete is heavy; backfill around the tube or brace it so it stays plumb while you fill it.
- Leave the top above grade. A few inches of tube above the ground keeps wood posts and brackets clear of soil and water.
- Set hardware while it is wet. Post bases and anchor bolts must go in before the concrete sets.
- Mix enough at once. Fill each tube in one continuous pour to avoid weak joints.
Frequently asked questions
How much concrete is in a 12-inch Sonotube?
A 12-inch tube holds about 0.785 cubic feet per foot of height. A 4-foot tube therefore takes about 3.14 cubic feet, or six 80 lb bags of concrete.
How many bags of concrete for a 10-inch Sonotube?
A 10-inch tube holds about 0.545 cubic feet per foot. A 4-foot tube needs about 2.2 cubic feet, which is four 80 lb bags or five 60 lb bags.
What size form tube do I need for deck footings?
Footing size depends on the load each post carries and on your soil, so it should come from your deck plans or local building code (in the US, the deck section of the IRC). Residential decks often use 8- to 12-inch tubes on top of a wider footing or bell base.
What is a bell footing?
A bell footing is a cone-shaped base, often a plastic form, that sits under the tube and spreads the load over a wider area of soil. Enter its bottom diameter and height and the calculator adds its volume to each tube.
Does this work for other brands of form tube?
Yes. Sonotube is a registered trademark of Sonoco; the calculator works for any round cardboard or plastic concrete form tube because it only uses the inside diameter and height.