Cubic yards and number of bags for any concrete pour.
For small jobs under 1 cubic yard, pre-mixed bags are most cost effective. One cubic yard (27 cu ft) requires about 45 bags of 60 lb mix. For larger pours, ready-mix delivery is more practical — standard trucks deliver 8–10 yards minimum.
A 4-inch slab is standard for patios and sidewalks. Driveways need at least 5–6 inches. Structural footings are specified by an engineer. Always add 10% overage — running out mid-pour is a serious problem.