B4
B4 highlighted — use the view toggle to see all 88 keys.
Piano key
51 of 88
Octave
4
Frequency
493.88 Hz
MIDI number
71
Key color
White key
Pitch class
B, Cb, A##
What is B4?
B4 is the B in octave 4 — the 51st key of the 88 on a full-size piano, counted from the bottom. In standard tuning it sounds at 493.88 Hz. It sits 11 half-steps above middle C (C4).
To find it, locate any group of two black keys: the white key just to their left is a C. Count up from middle C (C4) within the same octave to reach octave 4, then step to B.
Every octave doubles the frequency: the B one octave up sounds at 987.76 Hz and the one below at 246.94 Hz. The same piano key can be written as B, Cb, A## depending on the musical context — same sound, different spelling.
Nearby notes
Every B on the keyboard: