440 Hz is the pitch of A4, the A above middle C. ISO 16 makes it the standard tuning frequency: the A in the treble stave "shall be 440 Hz", and instruments that produce it for tuning should be accurate to within 0.5 Hz. The tone above is generated in your browser at exactly 440 Hz.
440 Hz at a glance
| Note | A4 (MIDI note 69), the A above middle C |
| Standard | ISO 16:1975, Acoustics: Standard tuning frequency (Standard musical pitch). Last confirmed by ISO in 2022. |
| Tuning accuracy in ISO 16 | Within 0.5 Hz (439.5 to 440.5 Hz) |
| One cycle lasts | 2.273 ms |
| Wavelength in air | About 0.78 m, at roughly 343 metres a second (room temperature) |
| Octave below / above | 220 Hz (A3) / 880 Hz (A5) |
Tuning an instrument to 440 Hz
- Turn your volume down, press Play, then raise it until the tone is clear but not loud.
- Play your A against it. If the two are slightly apart you will hear a slow wobble, called beating. The wobble rate in beats per second equals the difference in hertz: 2 beats a second means you are 2 Hz away.
- Adjust until the wobble slows and disappears. Then tune your other strings or notes from that A.
If you would rather see a reading, play your note into the pitch detector; it shows how many cents sharp or flat you are against A4 = 440 Hz.
The A notes across the keyboard
Each octave doubles the frequency, so every A is 440 Hz multiplied or divided by two.
| Note | Frequency | From A4 |
|---|---|---|
| A0 | 27.5 Hz | 4 octaves below |
| A1 | 55 Hz | 3 octaves below |
| A2 | 110 Hz | 2 octaves below |
| A3 | 220 Hz | one octave below |
| A4 | 440 Hz | Reference |
| A5 | 880 Hz | one octave above |
| A6 | 1,760 Hz | 2 octaves above |
| A7 | 3,520 Hz | 3 octaves above |
Notes near 440 Hz
| Note | Frequency at A4 = 440 Hz |
|---|---|
| C4 | 261.63 Hz |
| G4 | 392.00 Hz |
| G♯4 | 415.30 Hz |
| A4 | 440.00 Hz |
| A♯4 | 466.16 Hz |
| B4 | 493.88 Hz |
| C5 | 523.25 Hz |
Equal temperament: each semitone is the twelfth root of two (about 5.9%) above the last.
440 Hz, 442 Hz and 432 Hz
ISO 16 specifies 440 Hz. Some ensembles agree on a slightly different reference, so the generator lets you change A4 = and the buttons beside it play 442 Hz and 432 Hz for comparison. 432 Hz is not a standard tuning frequency. We make no claims about the effects of any frequency on health or wellbeing; a tone's effect on your ears depends on how loud it is, which you can read about on the decibel chart.
Other uses
- Speaker and headphone checks: almost any speaker or headphone can play 440 Hz clearly, which is why our speaker test and left and right test use it.
- Teaching: switch the waveform to hear the same pitch as sine, square, triangle and sawtooth.
- Test files: set a length and press Download WAV for an exact 440 Hz file at 44.1 or 48 kHz.
Need a different frequency? Type it into the box above or open the full tone generator.
Common questions
What note is 440 Hz?
A4, the A above middle C. It is the A on the second space of the treble stave.
Why is 440 Hz the standard pitch?
ISO 16, the international standard for musical pitch, sets the A in the treble stave at 440 Hz. ISO last confirmed the standard in 2022.
How accurate does a 440 Hz tuning tone need to be?
ISO 16 says instruments that produce the tuning note should be accurate to within 0.5 Hz. A browser tone is generated digitally at the exact frequency.
Is 432 Hz better than 440 Hz?
432 Hz is not a standard tuning frequency, and we make no claims about the effects of any frequency on health. You can play both on this page and compare them.
Last reviewed 14 November 2026 by Sri Murugan Systems. Found a mistake? Tell us.