The modern standard-sized piano has 88 keys, which equals 88 notes and covers a range of seven octaves plus a minor third. A few pianos are specially made with an extend bass range, such as the Imperial Bosendorfer, which has 97 keys and covers a range of eight full octaves.
The range of the piano has grown throughout history. The piano of Mozart's day had a range of only five octaves, or 60 keys. By 1810, the piano had reached a range of six octaves, or 72 keys. Several later compositions by Beethoven were written using this extended range. By the end of the 1800s, the 88-key keyboard had become standard.