Thirteenth floor

Generally, the floors of a building are numbered sequentially, from one or ground upwards. However, in some countries, including the United States and Canada, buildings will sometimes purposely omit the thirteenth floor, because in these countries 13 is considered an unlucky number.

Sometimes the floor is simply renumbered as 12a and at other times it is missed out altogether. In the latter case, although the thirteenth floor has been skipped in terms of numbering (i.e., for hotel/apartment/suite numbers), the floor numbered 14 is technically the thirteenth floor of the building; it is simply not numbered as such.

Other buildings will often use names for certain floors to avoid giving a floor on the building the 13th floor designation. One such example is the APAC Building in Cedar Rapids, Iowa. The building is 14 stories tall. However, the ground floor is called the Lobby. Because the city's downtown skywalk system connects to the building on the second floor, that floor is referred to as the Skywalk Floor. The third floor of the building is referred to as 1st Floor. The 13th floor is referred to as the 11th Floor. The top level - or the 14th floor - of the building is referred to as 12th Floor.

Any calculations involving the height of a building based on the height of a floor should take this into account (particularly in reference to BASE jumping).

Similarly, new buildings in some parts of South China omit the fourth (as well as the 14th, 24th, etc.) floors, as the figure "four" sounds like "death" in Cantonese, the predominant dialect for that region of the country.

Conspiracy theorists often suggest that the thirteenth floor in government buildings is not really missing, but actually contains top-secret governmental departments, or more generally that it is proof of something sinister or clandestine going on. This implication is often carried over, implicitly or explicitly, into popular culture; for example, in the films The Thirteenth Floor, Being John Malkovich, and the computer game Floor 13 by Virgin Interactive. It might be noted that to place a floor between those accessible from an elevator, it is necessary to either take longer to travel between the neighboring floors, or accelerate, which riders would feel.

See also: Triskaidekaphobia