432 Hz vs 440 Hz: What's the Real Difference?

Search for music tuning and you'll quickly find 432 Hz: "the frequency of the universe", "healing tuning", "what Mozart used". Meanwhile almost all modern music is tuned to 440 Hz. What's going on?

What the number means

The number is the frequency of the note A4, the A above middle C. It's the anchor for every other note: in standard tuning A4 is 440 Hz, and every other note is calculated from it. Tune A4 to 432 Hz instead and every note shifts down by the same proportion.

That shift is about 32 cents, roughly a third of a semitone. It's audible if you compare them back to back, but small: much smaller than the difference between two neighbouring piano keys.

Hear it yourself

Open the tone generator, play 440 Hz, then switch to 432 Hz. Most people can hear that 432 is slightly lower. Going back and forth, some describe it as a touch warmer or darker; others hear only "a bit flat". Neither is wrong.

Where 440 Hz came from

Before the 20th century, tuning varied a lot between cities and orchestras: A could be anywhere from about 400 to over 450 Hz. That made it hard for instruments and musicians to work together. A4 = 440 Hz was gradually adopted as an international standard during the 20th century, so a piano in Tokyo and a flute in London would agree. Today many orchestras tune slightly higher, around 442 Hz, for a brighter sound. Baroque ensembles often tune to 415 Hz to match historical instruments.

The claims about 432 Hz

You'll read that 432 Hz is mathematically special, matches the vibration of the earth, reduces stress or was used by classical composers. These claims don't hold up well:

• The numbers that make 432 look special depend on choosing seconds as the unit of time, which is a human convention.
• Historical tuning was all over the place, not settled at 432.
• Research on health effects is very limited. A few small studies have reported tiny differences, but nothing that supports the bigger claims.

So which should you use?

• Playing with other people or recordings: use 440 Hz (or whatever the group uses). Agreement matters far more than the number.
• Playing alone, for the sound: use whatever you like. If 432 Hz sounds better to you, that's a perfectly good reason.

The online tuner uses A4 = 440 Hz by default; the full version also tunes to 432, 442 or 415 Hz. The note frequency chart shows every note at either tuning.