Apartments can be classified into several types. Studio or efficiency or bachelor apartments tend to be the smallest apartments with the cheapest rents in a given area. These kinds of apartment usually consist mainly of a large room which is the living, dining, and bedroom combined. There are usually kitchen facilities as part of this central room, but the bathroom is its own smaller separate room. Moving up from the efficiencies are one-bedroom apartments where one bedroom is a separate room from the rest of the apartment. Then there are two-bedroom, three-bedroom, etc. apartments. Small apartments often have only one entrance/exit. Large apartments often have two entrances/exits, perhaps a door in the front and another in the back. Depending on the building design, the entrance/exit doors may be directly to the outside or to a common area inside, such as a hallway. Depending on location, apartments may be available for rent furnished with furniture or unfurnished into which a tenant usually moves in with his/her own furniture. Permanent carpeting is often included in an apartment.



Laundry facilities are usually kept in a separate area accessible to all the tenants in the building. Depending on when the building was built and the design of the building, utilities such as water, heating, and electric may be common for all the apartments in the building or separate for each apartment and billed separately to each tenant (however, many areas in the US have ruled it illegal to split a water bill among all the tenants, especially if a pool is on the premises). Outlets for connection to telephones are typically included in apartments. Telephone service is optional and is practically always billed separately from the rent payments. Cable television and similar amenities are extra also. Parking space(s), air conditioner, and extra storage space may or may not be included with an apartment. Rental leases often limit the maximum number of people who can reside in each apartment. On or around the ground floor of the apartment building, a series of mailboxes are typically kept in a location accessible to the public and, thus, to the letter-carrier too. Every unit typically gets its own mailbox with individual keys to it. Some very large apartment buildings with a full-time staff may take mail from the mailman and provide mail-sorting service. Near the mailboxes or some other location accessible by outsiders, there may be a buzzer (equivalent to a doorbell) for each individual unit. In smaller apartment buildings such as two- or three-flats, or even four-flats, garbage is often disposed of in trash containers similar to those used at houses. In larger buildings, garbage is often collected in a common trash bin or dumpster. For cleanliness or minimizing noise, many lessors will place restrictions on tenants regarding keeping pets in an apartment.

In some parts of the world, the word apartment is used generally to refer to a new purpose-built self-contained residential unit in a building, whereas the word flat means a converted self-contained unit in an older building. An industrial, warehouse, or commercial space converted to an apartment is commonly called a loft.

When part of a house is converted for the ostensible use of a landlord's family member, the unit may be known as an in-law apartment or granny flat, though these (sometimes illegally) created units are often occupied by ordinary renters rather than family members.

Staying in privately owned apartments rather than in a hotel is quickly becoming popular with travellers.