Enter slab length, width and thickness to get the concrete volume in cubic yards and the number of pre-mix bags.
Volume is length times width times thickness. One cubic yard is 27 cubic feet, and ready-mix trucks are ordered in cubic yards — always rounded up, because a short load costs far more in extra delivery fees than the spare concrete. Bag counts use the standard yields printed on pre-mix bags: an 80 lb bag makes about 0.60 cubic feet of concrete and a 60 lb bag about 0.45. Anything over roughly one cubic yard is usually cheaper and far less labour as a ready-mix delivery than as hand-mixed bags.
How thick should a concrete slab be? Four inches is standard for patios, paths and shed bases. Driveways carrying vehicles are usually 5 to 6 inches, often with reinforcement mesh or rebar.
How many 80 lb bags make a cubic yard? At 0.60 cubic feet per bag, one cubic yard (27 cubic feet) takes 45 bags of 80 lb pre-mix — which is why larger pours are normally ordered ready-mixed.