* For a room in a home: La salle de bain (bathroom) is often used, as dressing rooms are often incorporated into bathroom spaces.
* For a room in a store: La cabine d'essayage is the standard term for a fitting room.
* For a room in a theater: Le vestiaire is the general term for a cloakroom, which can also include dressing rooms for actors.
You can also use la salle de préparation (preparation room) or la loge (dressing room), particularly for theatrical settings.