A4
A440 — concert pitch
A4 highlighted — use the view toggle to see all 88 keys.
Piano key
49 of 88
Octave
4
Frequency
440 Hz
MIDI number
69
Key color
White key
Pitch class
A, G##, Bbb
What is A4?
A4 is the A in octave 4 — the 49th key of the 88 on a full-size piano, counted from the bottom. In standard tuning it sounds at 440 Hz, the pitch orchestras tune to. It sits 9 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 A.
Every octave doubles the frequency: the A one octave up sounds at 880 Hz and the one below at 220 Hz. The same piano key can be written as A, G##, Bbb depending on the musical context — same sound, different spelling.
Nearby notes
Every A on the keyboard: