A0 — 27.50 Hz
A0 (MIDI 21) vibrates 27.50 times per second at standard concert pitch. Play the reference tone below, or tune to it with the online tuner.
A0 at different reference pitches
| Reference (A4) | A0 frequency | Used for |
|---|---|---|
| 415 Hz | 25.94 Hz | Baroque pitch |
| 432 Hz | 27.00 Hz | “Verdi” pitch |
| 440 Hz | 27.50 Hz | Standard concert pitch |
| 442 Hz | 27.63 Hz | European orchestras |
| 444 Hz | 27.75 Hz | European orchestras |
Physical properties
- Period: one cycle every 36.36 ms
- Wavelength in air: ≈ 12.47 m (at 20 °C, 343 m/s)
- MIDI note number: 21
- Octave up: A1 = 55.00 Hz · Octave down: 13.75 Hz