What is 440 Hz?
440 Hz is the international standard pitch for the note A above middle C (A4), used to tune most modern instruments.
An international conference in London agreed on A = 440 Hz in 1939, and it was later adopted as the ISO 16 standard. Orchestras still vary a little — many tune to 442 Hz for a brighter sound — but 440 Hz is the reference built into tuners, phones and synthesizers.
The dial tone in North America is also partly 440 Hz (mixed with 350 Hz), so it is one of the most familiar frequencies in daily life.
| Nearest note (A4 = 440 Hz) | A4 (440 Hz), exactly in tune |
|---|---|
| Wavelength in air | 78 cm |
| Period | 2.27 ms per cycle |
| Simulator Chladni mode | (2, 1) |
What the 440 Hz pattern looks like
Classic Chladni mode at 440 Hz gives a clear, medium-density figure — a good starting point before sweeping up or down.
The simulator above is already set to 440 Hz. Press Play in the Slider tab to hear the tone, switch pattern modes to compare shapes, and use Record video or Export PNG to keep the result. The address bar always holds a link to exactly what you see, so you can share it.
440 Hz FAQ
Why is A tuned to 440 Hz?
It was chosen as an international compromise in 1939 to end wide differences in pitch between countries and orchestras, and later became the ISO 16 standard.
What is the wavelength of 440 Hz?
In air at room temperature (343 m/s), a 440 Hz sound wave is about 78 cm long.