How the concrete calculator works
Volume = length × width × thickness. We convert thickness from inches to feet, multiply to get cubic feet, then divide by 27 for cubic yards. Bag count comes from the yield printed on each bag, with a 10% waste factor for spillage and uneven subgrade.
Bags or ready-mix?
Bags make sense for small pours — under roughly 1 cubic yard (about 40–60 bags). Above that, ordering a ready-mix truck is cheaper and far less work. If your result is over a yard, call a local plant for a quote.
How thick should a slab be?
4 inches for patios, walkways, and shed floors; 5–6 inches for driveways and anything carrying vehicle weight. Add wire mesh or rebar for crack control.