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About A4
A4 (concert A) has a frequency of 440 Hz in standard tuning, where A4 is fixed at 440 Hz. It is MIDI note 69 and key number 49 on an 88-key piano.
A4 is concert pitch: the note orchestras tune to, standardised at 440 Hz by ISO 16.
In equal temperament every semitone multiplies the frequency by the twelfth root of two (≈1.05946), so A4 is 0 semitones away from A4: f = 440 × 2^((69 − 69) / 12) = 440.00 Hz. The number in the name is the octave in scientific pitch notation, which starts each octave on C.
A4 frequency in different tunings
| Tuning reference | A4 frequency |
|---|---|
| A4 = 440 Hz (ISO 16 standard) | 440 Hz |
| A4 = 442 Hz (many European orchestras) | 442 Hz |
| A4 = 443 Hz (Berlin, Vienna) | 443 Hz |
| A4 = 435 Hz (French diapason normal, 1859) | 435 Hz |
| A4 = 432 Hz (alternative tuning) | 432 Hz |
| A4 = 415 Hz (Baroque pitch) | 415 Hz |
| C4 = 256 Hz (scientific pitch) | 430.54 Hz |
Where to play A4 on a guitar
Standard tuning (E A D G B E), frets 0–22.
- 4th string (D), fret 19
- 3rd string (G), fret 14
- 2nd string (B), fret 10
- 1st string (high E), fret 5
Intervals from A4
| Interval | Note | Frequency | Ratio (just) |
|---|---|---|---|
| Minor second | A♯4 | 466.16 Hz | 16:15 |
| Major second | B4 | 493.88 Hz | 9:8 |
| Minor third | C5 | 523.25 Hz | 6:5 |
| Major third | C♯5 | 554.37 Hz | 5:4 |
| Perfect fourth | D5 | 587.33 Hz | 4:3 |
| Tritone | D♯5 | 622.25 Hz | 45:32 |
| Perfect fifth | E5 | 659.26 Hz | 3:2 |
| Minor sixth | F5 | 698.46 Hz | 8:5 |
| Major sixth | F♯5 | 739.99 Hz | 5:3 |
| Minor seventh | G5 | 783.99 Hz | 9:5 |
| Major seventh | G♯5 | 830.61 Hz | 15:8 |
| Octave | A5 | 880 Hz | 2:1 |
Instruments and voices that can play A4
- Piano (88 keys)
- Guitar (standard tuning)
- Violin
- Viola
- Cello
- Harp
- Flute
- Clarinet (B♭, sounding)
- Oboe
- Bassoon
- Alto saxophone (sounding)
- Tenor saxophone (sounding)
- Trumpet (B♭, sounding)
- French horn (sounding)
- Trombone
- Baritone voice
- Tenor voice
- Alto voice
- Mezzo-soprano voice
- Soprano voice
Frequently asked questions
What is the frequency of A4?
A4 is 440 Hz when A4 = 440 Hz (432 Hz if A4 = 432 Hz).
What MIDI number is A4?
A4 is MIDI note number 69.
Is A4 on a piano?
Yes – it is key 49 of 88.
Where is A4 on the guitar?
In standard tuning: 4th string (D), fret 19; 3rd string (G), fret 14; 2nd string (B), fret 10; 1st string (high E), fret 5.