Sonotube Concrete Calculator
Find how much concrete a Sonotube pier takes from tube diameter, depth and count — in cubic yards, cubic feet and bags.
How it works
per tube (cu ft) = π × (diameter ÷ 24)² × depth · 80 lb bags ≈ cu ft ÷ 0.60
A Sonotube forms a round pier, so the fill is a cylinder: π times the radius squared times the depth. The diameter is halved and divided by 12 to get the radius in feet. Each 80 lb bag of concrete mix yields about 0.60 cubic feet, so the bag count is the total cubic feet divided by 0.60, rounded up per tube so you never run a tube short.
Worked example
Six 12 in tubes poured 4 ft deep: radius 0.5 ft, each is π × 0.5² × 4 = 3.14 cu ft, so 5 eighty-pound bags per tube. Six tubes are 18.8 cu ft — 32 bags, or about 0.70 cubic yards of ready-mix.
Frequently asked questions
How many bags per tube?
Divide each tube’s cubic feet by 0.60 for 80 lb bags (or 0.45 for 60 lb) and round up per tube — a 12 in tube 4 ft deep needs about five 80 lb bags. Rounding per tube, not for the whole job, keeps every pier fully filled.
Should I overfill the tube?
Fill to the top and slightly mound it, then screed flush. Concrete settles as it is rodded and vibrated to release air, so a level top before consolidation often ends up low.
When should I switch to ready-mix?
Once the whole job passes roughly half a cubic yard — about 20 eighty-pound bags — mixing by hand becomes slow and inconsistent, and a short-load truck is cheaper for your time.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.