Andar vs. piso
When discussing building levels in Portuguese, you will encounter the words andar and piso. While they effectively translate to the English "floor" or "storey", their usage varies significantly between Brazil and Portugal. Andar is universally used for vertical levels, whereas piso has a dual meaning involving both building levels and the actual flooring material, depending on the region.
Andar
A2This word refers specifically to a storey or level of a building. It represents the vertical layers of a structure. In both Brazil and Portugal, andar is the standard term used when saying which floor an apartment or office is located on (e.g., first floor, second floor). It is generally not used to describe the ground floor.
Eu moro no terceiro andar deste prédio.
(I live on the third floor of this building.)
O elevador quebrou no quinto andar.
(The elevator broke down on the fifth floor.)
Eles construíram mais um andar na casa.
(They built one more storey on the house.)
O escritório fica no último andar.
(The office is located on the top floor.)
Prefiro não morar em um andar baixo por causa do barulho.
(I prefer not to live on a low floor because of the noise.)
Piso
A2This word has two primary contexts. First, it refers to the physical surface you walk on, such as pavement, tiles, or wood flooring; this is the dominant meaning in Brazil. Second, it means a building level or storey. In Portugal, piso is frequently interchangeable with andar and is the standard way to refer to the ground floor (piso 0) or technical levels. In Brazil, using piso to mean a building storey is mostly reserved for shopping malls, garages, or technical architectural descriptions.
Cuidado, o piso está molhado.
(Careful, the floor refers to the surface is wet.)
Estacionei o carro no piso inferior.
(I parked the car on the lower level.)
A loja de brinquedos fica no piso 2 do shopping.
(The toy store is on level 2 of the mall.)
Em Portugal, é comum entrar no edifício pelo piso zero.
(In Portugal, it is common to enter the building on floor zero.)
Nós vamos trocar o piso da sala de jantar.
(We are going to change the flooring of the dining room.)
Summary
To summarize, use andar in both Brazil and Portugal when talking about residential storeys (1st floor and up). Use piso when referring to the material on the ground (flooring). However, be aware that in Portugal and in commercial settings (like malls), piso is also widely used to mean a building level, exactly like andar.