C8 at a glance
All values assume twelve-tone equal temperament at the international standard pitch of A4 = 440 Hz. In that system every semitone has the same size - a frequency ratio of 2^(1/12) - so C8 is exactly 440 × 2^(39/12) Hz. Under alternative references the note shifts with the reference: at A4 = 432 Hz, C8 becomes 4109.9 Hz.
C in every octave
| Note | Frequency | MIDI | Piano key |
|---|---|---|---|
| C1 | 32.70 Hz | 24 | 4 |
| C2 | 65.41 Hz | 36 | 16 |
| C3 | 130.81 Hz | 48 | 28 |
| C4 | 261.63 Hz | 60 | 40 |
| C5 | 523.25 Hz | 72 | 52 |
| C6 | 1046.5 Hz | 84 | 64 |
| C7 | 2093.0 Hz | 96 | 76 |
| C8 ← | 4186.0 Hz | 108 | 88 |
Each octave doubles the frequency - the simplest relationship in music, and the reason notes an octave apart sound like “the same note, higher”.
Neighboring notes
One semitone down is B7 at 3951.1 Hz. C8 is the highest note on the piano. Need a frequency between notes, or a different waveform? The tone generator plays anything from 20 Hz to 20 kHz; the note ↔ frequency converter does the math both directions, and the chromatic tuner listens to your instrument and shows the offset in cents.