440 Hz: the standard tuning pitch

A4 = 440 Hz is the international standard reference for tuning, agreed at a conference in 1939 and published as ISO 16. Almost every tuner, keyboard, synthesizer and recording is set to it, which is why “A440” is the default in every tuner’s settings.

Every other note is derived from it: in equal temperament each semitone multiplies the frequency by the twelfth root of two, so the note an octave below is 220 Hz and the one an octave above is 880 Hz.

• Tune to A = 440 Hz with the chromatic tuner

Which note 440 Hz is at other reference pitches

“In tune” depends on what A4 is tuned to, so the same frequency is a slightly different distance from the nearest note in each tuning.

Octaves of 440 Hz

Doubling a frequency raises it an octave and halving lowers it one, so these all have the same note name.

• 55.00 Hz · A1
• 110.00 Hz · A2
• 220.00 Hz · A3
• 880.00 Hz · A5
• 1760.0 Hz · A6
• 3520.0 Hz · A7

Harmonics of 440 Hz

A real instrument playing 440 Hz also sounds whole-number multiples of it. The first eight, and the notes they fall nearest:

Period and wavelength

One cycle of 440 Hz lasts 2.273 milliseconds; in air at 20 °C, where sound travels at about 343 metres a second, one wavelength is 78.0 centimetres.

Convert another frequency

Or hold 440 Hz as a steady tone, sweep from it, or beat it against a second tone in the tone generator. The note frequency chart lists every note from C0 to B8.

Frequently asked questions

Related frequencies

• 432 Hz — an alternative tuning pitch
• 442 Hz — the orchestral tuning pitch
• 415 Hz — baroque pitch
• 443 Hz — a bright orchestral tuning pitch
• 432 vs 440: the blind test