Work out concrete for a slab, footing or pad in cubic yards and in 60 or 80 lb bags.
Concrete is a volume calculation: area × thickness, converted to yards for ready-mix or bags for hand-mixing.
Bagged mix makes sense up to roughly half a yard. Beyond about one cubic yard, ordering ready-mix delivered is cheaper and far less work. Always add ~10% for uneven subgrade and spillage.
About 45 bags. Each 80 lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 ≈ 45 bags. That volume is where ready-mix delivery usually becomes the better deal.
Four inches is standard for patios, walkways and shed floors. Bump to five or six inches for driveways and anywhere vehicles or heavy loads sit, and add rebar or wire mesh for strength.
Yes. Order about 10% more than the bare calculation to cover an uneven subgrade, over-dug edges and spillage. Running short mid-pour leaves a cold joint, which is far worse than a little leftover.
Once you pass roughly one cubic yard, bagged mix becomes slow and expensive. A ready-mix truck delivers a consistent batch in one pour, which also avoids the cold joints you get from mixing bag after bag.
The Home Renovation Project Manager rolls every calculator into one budget — room by room, with a shopping list, contractor quote comparison and a live over-budget warning.