Concrete for a 30×30 slab at 5" thick
A 30 ft × 30 ft slab poured 5 inches thick needs the amounts below (a 10% waste allowance is already included).
Concrete needed
15.28cubic yards
413
cubic feet
688
80 lb bags
917
60 lb bags
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For a slab this size, 15.28 cubic yards is usually cheapest as ready-mix delivery. About 688 bags of 80 lb mix would do it by hand.