C♯1 / D♭1
Reviewed for accuracy · Maintained by Justin Evans
C♯1 highlighted — use the view toggle to see all 88 keys.
Piano key
5 of 88
Octave
1
Frequency
34.65 Hz
MIDI number
25
Key color
Black key
Pitch class
C# · Db · B##
What is C♯1?
C♯1 is the C♯ in octave 1 — the 5th key of the 88 on a full-size piano, counted from the bottom. In standard tuning it sounds at 34.65 Hz. It sits 35 half-steps below middle C (C4).
To find it, locate any group of two black keys: the white key just to their left is a C. Count down from middle C (C4) 3 octaves to reach octave 1, then step to C♯.
Every octave doubles the frequency: the C♯ one octave up sounds at 69.3 Hz and the one below at 17.33 Hz. The same piano key can be written as C#, Db, B## depending on the musical context — same sound, different spelling.
Nearby notes
Every C♯ on the keyboard: