A 3cm slab is about one and a quarter inches thick. It is the standard for kitchen countertops in the United States: the edge already looks substantial without lamination, and the extra depth supports an overhang at a breakfast bar with less support underneath.
It is heavier to move and costs more per square foot than a thinner slab, so vanities and wall panels are often done in 2cm slabs. Compare stones in marble, quartzite and granite.
