A room number is a number assigned to a room within a building. Its purpose is to identify a particular room, and help building inhabitants locate that room. Logical and consistent assignment of room numbers is important for efficient everyday building usage, and to allow emergency personnel to quickly and easily find their way to any area of a building.

Room numbers may consist of three digits, but can be any number of digits. The room number is generally assigned with the first digit indicating the floor on which the room is located. For example, room 412 would be on the fourth floor of the building; room 540 would be on the fifth floor. Buildings that have more than nine floors will have four digits assigned to rooms beyond the ninth floor. For example, room 1412 would be on the 14th floor.

The second digit may represent the wing, or section, of the building in which the room is located: room 540 will typically be found adjacent to room 542, and room 532 adjacent to room 530. In a four digit room number, this digit will be the third digit instead of the second.