How many keys does a standard full-size piano have?

A full-size piano has 88 keys, 52 white and 36 black, spanning a little over seven octaves from the bottom A to the top C. That range was not always standard. Early pianos of Mozart's day had around five octaves, and makers extended the compass through the nineteenth century as composers wrote past the edges of the keyboard and as iron frames made it possible to hold the greater string tension. It settled at 88 partly for practical reasons: beyond the top of the range the strings are so short that the pitch loses definition, and below the bottom the notes turn into a rumble the ear struggles to identify. The keys themselves repeat a twelve-note pattern of seven white and five black, and the irregular grouping of black keys in twos and threes is what lets a player find position by touch without looking down.

The white keys are no longer ivory; the trade was banned and modern keys are plastic or occasionally bone substitutes.