Monica Geller’s apartment in Friends is apartment number 20.
The purple-walled apartment is one of the series’ primary sets and is where Monica lives with Rachel for much of the show. It hosts parties, romantic conversations, holiday gatherings, and many of the group’s arguments. After Rachel moves out, Monica shares the apartment with Chandler.
The apartment number is especially easy to confuse with Chandler and Joey’s neighboring apartment, which is number 19. The two doors face each other across the hallway, allowing the series to stage frequent comic interruptions and exchanges between the apartments.
Monica’s apartment number also reflects the characters’ presumed floor in the building. Early exterior shots and later dialogue created some continuity questions about the building’s layout, but the door number used for Monica’s apartment is 20. The number 20 therefore identifies Monica’s home, while 19 identifies the apartment across the hall.