A4 at every common reference pitch
A note’s frequency depends on what A4 is tuned to. The standard is 440 Hz; the other three are the ones you are most likely to meet. The cents column is how far each one sits from the 440 version — the same for every note, because changing the reference moves the whole scale together.
| Reference | A4 | vs 440 |
|---|---|---|
| A4 = 415 Hz · Baroque pitch | 415.00 Hz | −101.3¢ |
| A4 = 432 Hz · “Verdi” pitch | 432.00 Hz | −31.8¢ |
| A4 = 440 Hz · Standard (ISO 16) | 440.00 Hz | — |
| A4 = 442 Hz · Orchestral | 442.00 Hz | +7.9¢ |
One cycle of A4 lasts 2.273 ms, and its wavelength in air at 20 °C is 78.0 cm. Hold it as a steady tone in the tone generator.
A4 on the piano
A4 is key 49 of 88, counting from the bottom — a white key. Press any key below to compare it with its neighbours.
A4 on the guitar
In standard tuning A4 is played in 4 places: 4th (D) string, fret 19, 3rd (G) string, fret 14, 2nd (B) string, fret 10 and 1st (high E) string, fret 5. The same pitch in each place, with a different tone: lower strings sound warmer. Guitar music is written an octave higher than it sounds, so on a guitar part this note is printed as A5.
A4 on the staff
Instruments that can play A4
45 instruments play A4 within the normal range, and 3 reach it only at the extreme of theirs. Each links to its range chart; for a transposing instrument, the note on its part is shown.
Guitars and basses
Plucked and struck strings
Woodwind
Tuned percussion
Only at the extreme of their range
Voices: A4 is inside the typical range of the baritone, tenor, alto, mezzo-soprano and soprano. Test your own range.
The harmonics of A4
A played A4 is not one frequency. A string or a pipe also sounds whole-number multiples of it, and the mix of those harmonics is the instrument’s tone. Here is where the first eight land — and why the 7th sounds out of tune against a piano.
| Harmonic | Frequency | Nearest note | Off by |
|---|---|---|---|
| 1 (fundamental) | 440.00 Hz | A4 | 0¢ |
| 2 | 880.00 Hz | A5 | 0¢ |
| 3 | 1320.0 Hz | E6 | +2.0¢ |
| 4 | 1760.0 Hz | A6 | 0¢ |
| 5 | 2200.0 Hz | C♯7 | −13.7¢ |
| 6 | 2640.0 Hz | E7 | +2.0¢ |
| 7 | 3080.0 Hz | G7 | −31.2¢ |
| 8 | 3520.0 Hz | A7 | 0¢ |
Frequencies that land on A4
- 440 Hz — the standard tuning pitch
- 432 Hz — an alternative tuning pitch
- 442 Hz — the orchestral tuning pitch
- 443 Hz — a bright orchestral tuning pitch
- 444 Hz — a bright tuning pitch
- 435 Hz — the French diapason of 1859
- 430 Hz — a period tuning pitch
Frequently asked questions
What is the frequency of A4?
A4 is 440.00 Hz in equal temperament with A4 tuned to 440 Hz, the international standard. At A4 = 432 Hz it is 432.00 Hz, and at the orchestral A4 = 442 Hz it is 442.00 Hz.
Which octave is A4 in?
The number is the octave in scientific pitch notation, where each octave starts on C and C4 is middle C. A4 is in octave 4, 9 semitones above middle C. In Helmholtz notation, used in older books, it is written a′.
How do I play A4 on a piano?
A4 is key 49 of 88, counting from the bottom — a white key.
Which instruments can play A4?
45 of the instruments we chart play A4 within their normal range, including violin, viola, cello, erhu, guitar, and 3 more reach it only at the extreme of their range.
Typing it? A4 is also written A4. Convert any frequency on the Hz-to-note converter.