A0
27.5Hz at concert pitch
Press to hear a pure sine tone at this pitch.
MIDI note
21
Piano key
1
Octave
0
Frequency
27.5 Hz
Period
36.3636 ms
Wavelength
12.4727 m
Pitch class
A
Notation
SPN
MIDI is the note number synths and software pass around (0–127). Pitch class is the note without its octave — all the As share one.
At other reference pitches
| Reference (A4) | A0 frequency | Where you meet it |
|---|---|---|
| 432 Hz | 27 Hz | the alternative-tuning circle |
| 440 Hzstandard | 27.5 Hz | the ISO 16 standard — concert pitch |
| 442 Hz | 27.625 Hz | many European orchestras tune a touch sharp |
| 443 Hz | 27.688 Hz | some sharper continental orchestras |
Every row is A0 — only the A4 you tune to changes. A frequency scales straight with the reference: A0 at 432 Hz is the 440 Hz value times 432⁄440.
About this note
The lowest note on a standard 88-key piano — piano key 1. Below here the fundamental gets hard to hear as pitch rather than rumble; a grand's longest string is doing the work.
Move around
Every A
Chords with A in them
A appears in each of these — see the whole chord grid.