Thickness is a structural and budget decision, not an aesthetic one — and it narrows which slabs are available to you.
Roughly ¾ inch. Lighter and cheaper per slab, but exposed edges usually need a laminated build-up to avoid looking thin, and most installs want a plywood substrate underneath.
Roughly 1¼ inch, and the default for kitchen work in the US. Strong enough to span cabinet runs without a substrate, and it carries a mitred edge cleanly if you want a thicker look.
Large-format porcelain comes far thinner than stone. The weight saving is often what makes a project viable — cladding an occupied floor, or surfacing over an existing substrate without rebuilding it.
Not every material is stocked in every thickness. Committing to a stone and then discovering it only comes in 2cm — when your design assumed 3cm — means starting the selection over. Settle thickness first and the search narrows honestly.
If you want the look of a 6cm edge, that is a mitre: two pieces joined at 45° to form a hollow thick edge. It consumes more material and more shop time, so factor it into both budget and slab count.
Browse current stock — every slab lists its thickness.