Sonotube, Column & Footing Calculator
Add up the concrete for round tube forms (Sonotube-style columns) plus a rectangular footing, in cubic yards and bags.
Calculator
4 tubes plus the footing come to about 15.23 cu ft — 0.56 yd³ or 26 bags of 80 lb. A footing here is a concrete volume, not a structural design.
Deck footings, fence posts, porch piers and mailbox columns all use a round cardboard tube form, often over a square footing pad at the bottom. The volume is a cylinder plus a rectangular prism — easy to get wrong by hand, easy here. Enter the tube size and count, add the footing if you have one, and get the total in cubic feet, cubic yards and bags. A footing here is a concrete volume, not a structural design.
Formula
tube = π × (diameter_in ÷ 24)² × height_ft, per tube × quantity
footing = length × width × (thickness_in ÷ 12)
total cu ft = tubes + footing → yd³ = cu ft ÷ 27, bags = ceil(cu ft ÷ yield)
Dividing the diameter by 24 converts inches to a radius in feet in one step.
Worked example
4 tubes, 12 in diameter × 4 ft tall, over a 2 × 2 ft × 8 in footing:
- Each tube = π × (12 ÷ 24)² × 4 = 3.14 cu ft × 4 = 12.57 cu ft
- Footing = 2 × 2 × (8 ÷ 12) = 2.67 cu ft
- Total = 15.24 cu ft = 0.56 yd³ = 26 × 80 lb bags
Tubes, footings & bell bottoms
For deck and porch piers, many codes call for a footing pad wider than the tube (sometimes a bell-bottom base) to spread the load — that pad is exactly what the footing fields capture as extra volume. If your tubes differ in size, run each group separately and add the totals. Bagged mix suits a handful of piers; once you are pouring a dozen tall columns, price a short-load delivery. As always, the tube diameter, footing size and embedment depth for a load-bearing structure are set by a licensed engineer and your local code — this tool just tells you how much concrete that design needs.