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A0 · 27.50 Hz

A0 is piano key 1 of 88 and MIDI note 21 - the very bottom of the piano, more felt than heard - fundamental frequencies down here are below many speakers. Play the pure tone below, tune to it, or explore the note in every octave.

27.5Hz

Volume50%

Waveform

A0 at a glance

Frequency

27.50 Hz

Wavelength (in air)

12.47 m

MIDI note

21

Piano key

1 / 88

Octave

0

Enharmonic

—

All values assume twelve-tone equal temperament at the international standard pitch of A4 = 440 Hz. In that system every semitone has the same size - a frequency ratio of 2^(1/12) - so A0 is exactly 440 × 2^(-48/12) Hz. Under alternative references the note shifts with the reference: at A4 = 432 Hz, A0 becomes 27.00 Hz.

A in every octave

Note	Frequency	MIDI	Piano key
A0 ←	27.50 Hz	21	1
A1	55.00 Hz	33	13
A2	110.00 Hz	45	25
A3	220.00 Hz	57	37
A4	440.00 Hz	69	49
A5	880.00 Hz	81	61
A6	1760.0 Hz	93	73
A7	3520.0 Hz	105	85

Each octave doubles the frequency - the simplest relationship in music, and the reason notes an octave apart sound like “the same note, higher”.

Neighboring notes

A0 · 27.50 HzA♯0 · 29.14 Hz B0 · 30.87 Hz

A0 is the lowest note on the pianoOne semitone up is A♯0 at 29.14 Hz. Need a frequency between notes, or a different waveform? The tone generator plays anything from 20 Hz to 20 kHz; the note ↔ frequency converter does the math both directions, and the chromatic tuner listens to your instrument and shows the offset in cents.

A0 FAQ

What frequency is A0?

A0 is 27.50 Hz in twelve-tone equal temperament with the standard reference of A4 = 440 Hz. Every semitone step multiplies the frequency by the twelfth root of two (about 1.0595), and A0 sits 48 semitones below A4.

What MIDI number and piano key is A0?

A0 is MIDI note 21 and key 1 of 88 on a standard piano. Octave numbering follows scientific pitch notation, where middle C is C4 (MIDI 60).

How do I tune to A0?

Play the tone above and match your instrument by ear until the beating between the two pitches slows and disappears, or use the chromatic tuner with your microphone for a cents readout. Small mistunings show up as slow beats: one beat per second at this pitch means you are about 61.8 cents off.

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