Calculate concrete volume and bag count for any sonotube or tube form diameter and depth. Covers 6-inch to 24-inch tubes and multiple piers at once — perfect for deck builders and foundation crews.
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Shop Express Tools →Sonotube concrete volume = π × (diameter/2)² × depth (all in feet). A 12" diameter tube at 48" (4 ft) deep = π × 0.5² × 4 = 3.14 CF. One 80 lb bag fills 0.60 CF, so that’s about 6 bags per pier. Add 10% waste.
A sonotube is a cylinder, so the volume calculation uses the formula for a cylinder:
| Tube Diameter | 36" deep | 48" deep | 60" deep |
|---|---|---|---|
| 8" | 1.05 CF / 2 bags | 1.40 CF / 3 bags | 1.74 CF / 3 bags |
| 10" | 1.64 CF / 3 bags | 2.18 CF / 4 bags | 2.73 CF / 5 bags |
| 12" | 2.36 CF / 4 bags | 3.14 CF / 6 bags | 3.93 CF / 7 bags |
| 14" | 3.21 CF / 6 bags | 4.28 CF / 8 bags | 5.35 CF / 9 bags |
| 16" | 4.19 CF / 7 bags | 5.59 CF / 10 bags | 6.98 CF / 12 bags |
| 18" | 5.30 CF / 9 bags | 7.07 CF / 12 bags | 8.84 CF / 15 bags |
Bag counts based on 80 lb bags (0.60 CF each). Add 10% waste. For 60 lb bags (0.45 CF each), divide CF by 0.45.
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Start free trialA 12-inch diameter sonotube that is 4 feet deep requires approximately 3.14 cubic feet of concrete, or about 6 bags of 80 lb concrete (at 0.60 cu ft per bag).
Deck post pier size depends on load and frost depth. A common rule of thumb is 3× the post width — so a 4×4 post uses a 12" tube, and a 6×6 post uses an 18" tube. Always check local building codes and engineer specs.
Sonotubes for deck footings must extend below the frost line in your area. Frost depths range from 12" in the south to 60"+ in northern climates. Check your local frost depth map or building department for the required depth.
Yes. Sonotubes (fiber tube forms) can be used above grade for decorative concrete columns or exposed pier applications. The tube is typically stripped after the concrete cures. Use a wax-coated tube for exposed applications.
One 80 lb bag fills 0.60 cubic feet. For a 10" tube at 3 ft deep, you need about 1.64 cu ft — so 3 bags per tube. Use this calculator to get the exact bag count for your diameter and depth.