The human hearing range is generally taken as being 20 Hertz to 20kHz, and so musicians might wonder:
The answer: 10.
Sound frequency doubles with each octave, so if we start from the lowest audible C note, “C0”, that’s at 16.35Hz. Note that’s even lower than the lowest note on a piano and just a smidge below the limit of the “official” human hearing range.
Then middle C is four octaves up, at “C4” or 261.63Hz – which you can find just by doubling 16.35 four times. Continuing to double, octave-by-octave, you eventually reach “C8” (the highest C on a piano) at 4186.01Hz or about 4.2kHz.
Finally you start approaching the limits of the human hearing range with “C10”, at 16744.04Hz or 16.7kHz, 10 octaves above our starting note.
To learn more about note frequencies and frequency bands read the Frequency Fundamentals series.