Sonotube Concrete Calculator
Concrete for round column forms — deck footings, porch posts, mailbox and sign bases.
This Sonotube concrete calculator works out the concrete for a round column form — deck and porch footings, fence and sign posts, and pier foundations — from the tube diameter and the pour depth.
Pick the circle shape in the tool, enter the inside diameter and how deep the footing goes, and set the number of footings to get a total for the whole deck at once.
Concrete per tube
An 8-inch tube uses about 0.35 cubic feet per foot of depth; a 10-inch tube about 0.55; a 12-inch tube about 0.79. A 10-inch footing poured 4 feet deep needs roughly 2.2 cubic feet — about four 60 lb bags or three 80 lb bags.
If the footing flares to a wider base (a bell or a poured pad under the tube), add that volume separately as a short cylinder or a rectangular pad.
Depth and diameter
Footings must reach below the local frost line — often 36 to 48 inches in cold regions, shallower in the south. Diameter follows the load and your building code: 8 inches for light structures, 10 to 12 inches for deck posts, larger for tall porch columns. Check the deck span tables or your inspector.
Order 10% extra. Cardboard tubes bow slightly under the weight of wet concrete, so the real volume runs a little over the nominal.
Bags or ready-mix
A handful of footings is bag work. Once you are past roughly 10 to 12 footings, or half a cubic yard total, a ready-mix delivery with a chute or a mixing trailer saves hours and gives a more consistent mix.
Common footing mistakes
Not reaching the frost line. A footing above frost depth heaves every winter — check the required depth with your building department.
Undersized tubes. Diameter follows the load per post from the span tables; deck posts are usually 10 or 12 inch.
No gravel under the tube. A few inches of compacted stone lets water drain away from the footing base.
Forgetting the flare. If the base bells out or sits on a poured pad, add that volume separately.
| Product | Yield | Per cubic yard | Best for | Notes |
|---|---|---|---|---|
| Ready-mix (delivered) | 1 yd³ per yd³ | — | Slabs, driveways, footings > ½ yd³ | Short-load fee under ~1 yd³ |
| 80 lb bag | ~0.60 ft³ | 45 bags | Small pads, posts, repairs | ~4,000 psi mixed |
| 60 lb bag | ~0.45 ft³ | 60 bags | Post setting, small footings | Common fence-post size |
| 50 lb bag | ~0.375 ft³ | 72 bags | Small repairs | |
| 40 lb bag | ~0.30 ft³ | 90 bags | Patching, setting small posts | |
| Cured concrete weight | — | ~4,000 lb (2 tons) | — | 145–150 lb/ft³ |
Every material calculator
Each of these uses the same measured-drawing tool with the right density and bag sizes built in: gravel calculator , mulch calculator , concrete calculator , concrete slab calculator , sand calculator , topsoil calculator , paver sand calculator , crushed stone calculator , pea gravel calculator , river rock calculator , decomposed granite calculator , road base calculator . Or start from the material calculator homepage and pick a material there.
Frequently asked questions
How much concrete do I need for a Sonotube?
Per foot of depth: about 0.35 cubic feet for an 8-inch tube, 0.55 for a 10-inch, and 0.79 for a 12-inch. Multiply by the footing depth and the number of footings.
How many bags of concrete for a 10 inch Sonotube 4 feet deep?
About 2.2 cubic feet — roughly four 60 lb bags or three 80 lb bags. Add one spare.
How deep should deck footings be?
Below the frost line for your area — commonly 36 to 48 inches in cold climates. Your local building department publishes the required depth.
What diameter Sonotube for a deck?
Typically 10 or 12 inches for deck posts, sized to the load on each footing from the span tables. Light structures may use 8 inches.
How many 80 lb bags of concrete per cubic yard?
About 45. A cubic yard is 27 cubic feet and an 80 lb bag yields roughly 0.6 cubic feet.
Should I order extra concrete for tube forms?
Yes, about 10%. Cardboard tubes bulge slightly under wet concrete, so actual volume exceeds the nominal.
When should I use ready-mix instead of bags for footings?
Past about 10 to 12 footings or half a cubic yard total, ready-mix is faster and more consistent than mixing dozens of bags.
Do I need gravel at the bottom of a Sonotube?
A few inches of compacted gravel under the tube aids drainage and gives a firm bearing, but many footing designs bear directly on undisturbed soil or a poured pad — follow your code.
How much concrete for a 12 inch Sonotube 4 feet deep?
π × (0.5)² × 4 = 3.14 cubic feet — about six 80 lb bags or a bit over 0.11 cubic yards. Add one spare bag.
How many bags of concrete per Sonotube?
An 8-inch tube uses about 0.6 of an 80 lb bag per foot of depth, a 10-inch about 0.9, and a 12-inch about 1.3.
Can I use ready-mix for Sonotubes?
Yes, and past about 10 to 12 footings it is faster and more consistent. A chute or a wheelbarrow feeds the tubes directly.
Do Sonotubes need rebar?
Most residential deck footings use a vertical rebar cage or a single dowel tying the footing to the pier, per local code. Check with your inspector.
How far above grade should a Sonotube finish?
Trim the tube 1 to 2 inches above finished grade and crown the top so water sheds away from the post base.