A2
A2 highlighted — use the view toggle to see all 88 keys.
Piano key
25 of 88
Octave
2
Frequency
110 Hz
MIDI number
45
Key color
White key
Pitch class
A, G##, Bbb
What is A2?
A2 is the A in octave 2 — the 25th key of the 88 on a full-size piano, counted from the bottom. In standard tuning it sounds at 110 Hz. It sits 15 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) 2 octaves to reach octave 2, then step to A.
Every octave doubles the frequency: the A one octave up sounds at 220 Hz and the one below at 55 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: