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Concrete for round tube forms: cubic feet and bags per Sonotube, the total for every pier, cubic yards for a truck and how many 4 ft tubes to buy.
With these inputs:
| Result | Value |
|---|---|
| 80 lb bags of concrete | 23 bags |
| Concrete per tube | 2.18 cu ft (4 bags) |
| Total concrete | 13.74 cu ft |
| Cubic yards | 0.51 cu yd |
| 4 ft tubes to buy | 6 |
| Weight of bags | 1,840 lb |
| Per tube | π × (10 ÷ 24)² × 4 = 2.18 cu ft |
| All tubes | 2.18 × 6 × 1.05 = 13.74 cu ft |
| Bags | ceil(13.74 ÷ 0.6) = 23 |
Bag yields are QUIKRETE Concrete Mix's. Above roughly 1 cubic yard, compare the bag price with a short-load ready-mix delivery. Diameter and depth come from your plans and local frost depth — this counts concrete, it doesn't size the footing.
A tube form (Sonotube is Sonoco's brand name; QUIKRETE sells QUIK-Tube) turns each footing into a cylinder, so the concrete is π × radius² × depth. Pick the tube diameter, how deep you'll fill it and how many piers you have, then the bag size you'll buy. The calculator returns the concrete per tube, the bags for one tube and for the whole job, cubic yards if you're ordering a truck, and the 4 ft tubes to buy.
π × radius² × depth. A 10 in tube is 5 in (0.417 ft) in radius, so 4 ft of it holds π × 0.417² × 4 = 2.18 cu ft. A 12 in tube 4 ft deep holds 3.14 cu ft, an 8 in tube 1.40 cu ft and a 6 in tube 0.79 cu ft.
For 4 ft of a 12 in tube, six 80 lb bags or seven 60 lb bags. The tube holds 3.14 cu ft; an 80 lb bag yields about 0.60 cu ft and a 60 lb bag 0.45 cu ft. QUIKRETE's own QUIK-Tube table gives the same counts.
A 4 ft, 10 in tube takes four 80 lb bags (2.18 cu ft) and a 4 ft, 8 in tube takes three (1.40 cu ft). For 3 ft, it's three bags for 10 in and two for 8 in.
When the job passes about a cubic yard (27 cu ft, about 45 bags of 80 lb). Twelve 12 in tubes 4 ft deep need 37.7 cu ft — 1.4 cu yd or 63 bags — which is a lot of hand mixing. Ask local suppliers for a short-load price and compare it with the bags.
Tube forms usually come in 4 ft lengths. If each pier is 2 ft or less, one tube cuts into two or more forms; a 3 ft pier uses one tube and leaves a 1 ft offcut. The calculator counts whole tubes from your depth and number of piers.
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