Find how many 40, 60 or 80 lb concrete bags you need for a slab, footing or post holes. Free, instant, includes waste.
Each 80 lb bag of premixed concrete yields about 0.60 cu ft, a 60 lb bag about 0.45 cu ft and a 40 lb bag about 0.30 cu ft. We multiply length × width × thickness, add waste, then divide by bag yield.
About 45 bags (27 ÷ 0.6).
Yes, 5–10% covers spills and uneven ground.