C1
Reviewed for accuracy · Maintained by Justin Evans
C1 highlighted — use the view toggle to see all 88 keys.
Piano key
4 of 88
Octave
1
Frequency
32.7 Hz
MIDI number
24
Key color
White key
Pitch class
C · B# · Dbb
What is C1?
C1 is the C in octave 1 — the 4th key of the 88 on a full-size piano, counted from the bottom. In standard tuning it sounds at 32.7 Hz. It sits 36 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 65.4 Hz and the one below at 16.35 Hz. The same piano key can be written as C, B#, Dbb depending on the musical context — same sound, different spelling.
Nearby notes
Every C on the keyboard: