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About A2
A2 has a frequency of 110 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 45 and key number 25 on an 88-key piano.
A2 is the open fifth string of the guitar.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so A2 is 24 semitones below A4: f = 440 × 2^((45 − 69) / 12) = 110.00 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
A2 frequency in different tunings
| Tuning reference | A2 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 110 Hz |
| A4 = 442 Hz (many European orchestras) | 110.5 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 110.75 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 108.75 Hz |
| A4 = 432 Hz (alternative tuning) | 108 Hz |
| A4 = 415 Hz (Baroque pitch) | 103.75 Hz |
| C4 = 256 Hz (scientific pitch) | 107.63 Hz |
Where to play A2 on a guitar
Standard tuning (E A D G B E), frets 0–22.
- 6th string (low E), fret 5
- 5th string (A), open
Intervals from A2
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | A♯2 | 116.54 Hz | 16:15 |
| Major second | B2 | 123.47 Hz | 9:8 |
| Minor third | C3 | 130.81 Hz | 6:5 |
| Major third | C♯3 | 138.59 Hz | 5:4 |
| Perfect fourth | D3 | 146.83 Hz | 4:3 |
| Tritone | D♯3 | 155.56 Hz | 45:32 |
| Perfect fifth | E3 | 164.81 Hz | 3:2 |
| Minor sixth | F3 | 174.61 Hz | 8:5 |
| Major sixth | F♯3 | 185 Hz | 5:3 |
| Minor seventh | G3 | 196 Hz | 9:5 |
| Major seventh | G♯3 | 207.65 Hz | 15:8 |
| Octave | A3 | 220 Hz | 2:1 |
Instruments and voices that can play A2
Frequently asked questions
What is the frequency of A2?
A2 is 110 Hz when A4 = 440 Hz (108 Hz if A4 = 432 Hz).
What MIDI number is A2?
A2 is MIDI note number 45.
Is A2 on a piano?
Yes – it is key 25 of 88.
Where is A2 on the guitar?
In standard tuning: 6th string (low E), fret 5; 5th string (A), open.