Why does a piano have 88 keys?

Answer 1

Not all pianos have 88 keys, although most modern pianos do. Pianos have roughly 88 keys because of the reach of the the player. Early pianos often had 85 keys. There was pressure to standardise on a number because composers wouldn't want to to write for keyboards if not all pianos could play them. Some modern keyboards have extra keys; usually these are hidden under a flap that can be raised if required - some jazz players like to have the extra bass notes. Having the extra notes also adds resonounce to other (conventional) bass notes.