What 88 keys cover
A piano’s keys span seven full octaves, plus a few extra notes at either end. The lowest is A0; the highest is C8. Each neighboring key moves up by one semitone, the smallest standard step in Western musical scales. Together, the keys cover the notes most commonly used in piano music, from deep bass to bright treble.
Why the range has limits
A key does not make a sound by itself: pressing it sets a hammer in motion, and the hammer strikes a string. Low notes need long, thick strings to vibrate slowly; high notes come from short, thin strings that vibrate quickly. Extending the range means pushing those physical differences further, while the resulting pitches can become less useful musically.
Human hearing also shapes what counts as a practical range. At the low end, very deep tones can be felt as much as heard, and at the high end, pitches may sound faint or difficult to distinguish. Notes outside the piano’s standard span are possible on some instruments, but they do not necessarily add clearly recognizable musical information.
A shared range for players and composers
The 88-key layout gives pianists a broad range without making the instrument unwieldy, and it provides composers with a consistent set of endpoints. That standard is why a piece written for piano can generally be played on another modern piano without the player having to adjust for a different number of keys.
