The ground floor and first floor in British and American English

There is a small but important difference in the naming of floors in British and American English.

In British English the floor of a building at street level is called the ground floor (in Polish parter). The floor above it is the first floor (in Polish pierwsze piętro) and the floor below is called the basement (in Polish piwnica). This floor numbering scheme is used in the majority of European countries.

In American English, however, the floor at street level is usually called the first floor. Go up one floor and you are on the second floor (which, of course, is the first floor for the British). The floor below street level is called the basement, the same as in British English. This scheme is used in such countries as the United States, Canada, China, Japan, Norway, Russia, and ex-Soviet states. The US system reduces confusion, particularly where a building has two main entrances, at different floor levels.

British English: ground floor, 1st floor, 2nd floor, 3rd floor, etc.
American English: 1st floor, 2nd floor, 3rd floor, 4th floor, etc.

Storey, storeys (British English) / story, stories (American English)

Another important word to consider here is storey (in Polish kondygnacja). This word describes the level (height) of a building and the total number of its floors. A storey is used to count floors above the ground line while floors of a building include the basements as well. Thus we say that a building has seven storeys, or is a seven-storey building.

From the word ‘storey’ we get single-storey and multi-storey buildings. A two-storey house or home extension is sometimes referred to as double-storey in the UK, while one storey is referred to as single-storey.