Sonotube Calculator

How it’s calculated

Volume per tube = π × (diameter ÷ 24)² × height, in cubic feet (diameter in inches ÷ 24 is the radius in feet). Total = per tube × count; cubic yards = total ÷ 27. Bags = total ÷ the yield of one bag, rounded up — an 80-lb bag of concrete mix yields about 0.60 cu ft (Quikrete; 60 lb ≈ 0.45, 50 lb ≈ 0.375).

Worked example

One 12-inch tube, 4 ft tall: π × (12 ÷ 24)² × 4 = π × 0.25 × 4 ≈ 3.14 cu ft (0.12 cu yd). With 80-lb bags (0.60 cu ft each): ⌈3.14 ÷ 0.60⌉ = 6 bags.

FAQs

How many bags of concrete per tube?

Divide the tube's cubic feet by one bag's yield and round up. By that math an 80-lb bag (~0.60 cu ft) fills very little of a big tube — a 12-inch × 4-ft pier already needs ~6 bags, so bagged mix gets impractical fast. Past a few tubes, ready-mix by the cubic yard is usually cheaper and easier.

Where do the bag yields come from?

They're the published yields for Quikrete Concrete Mix — 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 50 lb ≈ 0.375. Other brands are close but not identical; check your bag and round up, and mix a little extra for spillage and slightly oversized holes.

What diameter and depth do I need?

That's a structural and code question, not a volume one — pier diameter and depth depend on the load and your local frost line (footings must bear below it). This tool sizes the concrete once you know the dimensions; it doesn't design the footing.

Sources

• Volume = π × (diameter ÷ 24)² × height (geometry). Bag yields: Quikrete Concrete Mix published values (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45, 50 lb ≈ 0.375) — confirm against your bag.