Estimate concrete for round columns, sonotubes, or piers — volume in cubic yards plus bag counts — from the diameter, height, and quantity.
V = π × (diameter ÷ 2)² × height × count
A round column's volume is pi times the radius squared times the height. Multiply by the number of columns.
Cardboard form tubes (Sonotube) use this same volume — enter the tube's inside diameter.
Two things set how deep a column or pier footing goes: frost and load. In cold climates, footings must extend below the frost line — the depth to which the ground freezes — or frost heave will lift and crack the structure. That depth ranges from a foot or so in mild regions to four feet or more in the north, and it's set by local code. The deeper the footing, the more concrete each column uses.
Load matters too. A deck post carrying a corner of a roof needs a wider, deeper footing than one carrying open deck framing. Many tube footings flare into a belled or footed base to spread the load over more soil — that bell adds concrete volume beyond the straight cylinder this calculator computes, so add it separately if your design includes one.
Cardboard form tubes — Sonotube is the common brand — are the usual way to pour round columns and piers. When estimating, use the tube's actual inside diameter, not its nominal label, since the wall thickness slightly reduces the inside dimension. The tube also wants to float when you pour, so it must be braced plumb and backfilled before filling, or it will lift and lean.
For multiple footings, the calculator's count field saves you the multiplication, but remember that real sites vary: one hole always seems to be deeper than the rest, and soft spots swallow concrete. The 10% waste factor covers normal variation, but if your holes are rough or you've over-dug, carry a bit more.
Building a deck on six footings, each a 12-inch diameter Sonotube poured 4 ft deep. One column is π × (0.5 ft)² × 4 ft = 3.14 cubic feet. Six columns is 18.8 cubic feet, or 0.70 cubic yards before waste.
With 10% waste that's about 0.77 yards — right at the bag-versus-ready-mix line. At roughly 0.6 cubic feet per 80 lb bag, you'd need about 35 bags. For six footings that's manageable by hand with a mixer, but if you had twenty footings you'd call for ready-mix with a pump or wheelbarrow.
Volume is exact geometry. Bag yields match Quikrete and ASTM C387; add waste for over-pour.
About 0.29 cubic yards, or roughly 14 bags of 80 lb mix.
Below the local frost line, which varies from about 12 inches in mild climates to 48 inches or more in cold regions. Check your local building code — frost depth is the controlling factor for footing depth.
A 12-inch tube holds about 0.79 cubic feet per foot of depth; an 8-inch tube about 0.35. Multiply by the depth and the number of tubes, then add waste.
For a handful of footings, bags are practical. For a deck with twenty footings or large-diameter piers, ready-mix with a pump or wheelbarrow chain saves significant labor.