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About C♯0
C♯0 / D♭0 has a frequency of 17.32 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 13, outside the range of a standard piano.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so C♯0 is 56 semitones below A4: f = 440 × 2^((13 − 69) / 12) = 17.32 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
C♯0 and D♭0 are enharmonic: on a piano or in equal temperament they are the same key and the same frequency, but they are spelled differently depending on the key signature.
C♯0 frequency in different tunings
| Tuning reference | C♯0 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 17.32 Hz |
| A4 = 442 Hz (many European orchestras) | 17.4 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 17.44 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 17.13 Hz |
| A4 = 432 Hz (alternative tuning) | 17.01 Hz |
| A4 = 415 Hz (Baroque pitch) | 16.34 Hz |
| C4 = 256 Hz (scientific pitch) | 16.95 Hz |
Intervals from C♯0
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | D0 | 18.35 Hz | 16:15 |
| Major second | D♯0 | 19.45 Hz | 9:8 |
| Minor third | E0 | 20.6 Hz | 6:5 |
| Major third | F0 | 21.83 Hz | 5:4 |
| Perfect fourth | F♯0 | 23.12 Hz | 4:3 |
| Tritone | G0 | 24.5 Hz | 45:32 |
| Perfect fifth | G♯0 | 25.96 Hz | 3:2 |
| Minor sixth | A0 | 27.5 Hz | 8:5 |
| Major sixth | A♯0 | 29.14 Hz | 5:3 |
| Minor seventh | B0 | 30.87 Hz | 9:5 |
| Major seventh | C1 | 32.7 Hz | 15:8 |
| Octave | C♯1 | 34.65 Hz | 2:1 |
Frequently asked questions
What is the frequency of C♯0?
C♯0 is 17.32 Hz when A4 = 440 Hz (17.01 Hz if A4 = 432 Hz).
What MIDI number is C♯0?
C♯0 is MIDI note number 13.
Is C♯0 on a piano?
No – a standard 88-key piano runs from A0 to C8, so C♯0 is outside its range.