Floor numbering

A storey (British English) or story (American English; see spelling differences) is any level part of a building that could be used by people (for living, work, storage, recreation, etc.). The plurals are "storeys" and "stories" respectively.

The terms "floor", "level", or "deck" can also be used in this sense, except that one may use "ground floor" and "ground level" for the floor closer to what is considered the ground or street level. The words "storey" and "floor" also generally exclude levels of the building that have no roof, even if they are used by people—such as the terrace on the top roof of many buildings.

Houses commonly have only one or two floors. Buildings are often classified as low-rise, mid-rise and high-rise according to how many levels they contain, but these categories are not well-defined. The tallest skyscraper in the world, Burj Khalifa, has 163 floors. As of 2013^[update], the tallest planned skyscraper, Sky City, is planned to have 202 floors.

The height of each storey is based on the ceiling height of the rooms plus the thickness of the floors between each pane. Generally this is around 10 feet (3 m) total; however, it varies widely from just under this figure to well over it. Storeys within a building need not be all the same height — often the lobby is more spacious, for example. Additionally, higher levels may be smaller in volume than the ones beneath them (a prominent feature of the Willis Tower).

In English, the principal floor or main floor of a house is the floor that contains the chief apartments; it is usually the ground floor, or the floor above. In Italy the main floor of a home is usually above the ground level, and may be called the piano nobile ("noble floor").

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