55.0Hz
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55 HzFrequency at A4 = 440 Hz
33MIDI note number
13Piano key (of 88)
6.24 mWavelength in air
About A1
A1 has a frequency of 55 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 33 and key number 13 on an 88-key piano.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so A1 is 36 semitones below A4: f = 440 × 2^((33 − 69) / 12) = 55.00 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
A1 frequency in different tunings
| Tuning reference | A1 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 55 Hz |
| A4 = 442 Hz (many European orchestras) | 55.25 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 55.38 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 54.38 Hz |
| A4 = 432 Hz (alternative tuning) | 54 Hz |
| A4 = 415 Hz (Baroque pitch) | 51.88 Hz |
| C4 = 256 Hz (scientific pitch) | 53.82 Hz |
Intervals from A1
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | A♯1 | 58.27 Hz | 16:15 |
| Major second | B1 | 61.74 Hz | 9:8 |
| Minor third | C2 | 65.41 Hz | 6:5 |
| Major third | C♯2 | 69.3 Hz | 5:4 |
| Perfect fourth | D2 | 73.42 Hz | 4:3 |
| Tritone | D♯2 | 77.78 Hz | 45:32 |
| Perfect fifth | E2 | 82.41 Hz | 3:2 |
| Minor sixth | F2 | 87.31 Hz | 8:5 |
| Major sixth | F♯2 | 92.5 Hz | 5:3 |
| Minor seventh | G2 | 98 Hz | 9:5 |
| Major seventh | G♯2 | 103.83 Hz | 15:8 |
| Octave | A2 | 110 Hz | 2:1 |
Instruments and voices that can play A1
Frequently asked questions
What is the frequency of A1?
A1 is 55 Hz when A4 = 440 Hz (54 Hz if A4 = 432 Hz).
What MIDI number is A1?
A1 is MIDI note number 33.
Is A1 on a piano?
Yes – it is key 13 of 88.