Length × width × thickness
Yards for the truck, bags for the mixer, steel for the cart — one set of inputs, the whole shopping list.
| Bag size | Exact | Buy (with spare) |
|---|
Reinforcement
Concrete is only as good as what it sits on. Strip the topsoil, compact 4″ of gravel, and keep the forms square and level — the excavation is shallow, but it's still digging, and buried lines don't care how shallow you meant to go. The slab itself is the easy pour: even, screeded, and left alone to cure.
4″ for patios, walks, and shed floors; 5–6″ where vehicles park or drive. Thicker beats stronger mix for point loads — and every slab wants a compacted gravel base under it.
A 10×10 patio at 4″ is 33 cubic feet — 62 eighty-pound bags once the spare margin is counted. That's mixer territory but on the edge; the readout above flags the moment a ready-mix truck becomes the better deal.
Either, placed mid-slab — not lying on the base. #3 bar on an 18″ grid suits driveways and anything vehicles touch; remesh sheets are fine for patios and walks. The calculator counts both so the store trip is one trip.
A floating patio slab rides the seasons as one piece and mostly shrugs it off. Anything attached to a building, or carrying posts and walls, wants frost-depth footings at its edges — your state's number is here.