C♯4 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 C♯4 is exactly 440 × 2^(-8/12) Hz. Under alternative references the note shifts with the reference: at A4 = 432 Hz, C♯4 becomes 272.14 Hz.
C♯ in every octave
| Note | Frequency | MIDI | Piano key |
|---|---|---|---|
| C♯1 | 34.65 Hz | 25 | 5 |
| C♯2 | 69.30 Hz | 37 | 17 |
| C♯3 | 138.59 Hz | 49 | 29 |
| C♯4 ← | 277.18 Hz | 61 | 41 |
| C♯5 | 554.37 Hz | 73 | 53 |
| C♯6 | 1108.7 Hz | 85 | 65 |
| C♯7 | 2217.5 Hz | 97 | 77 |
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 C4 at 261.63 Hz; one semitone up is D4 at 293.66 Hz. 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.