What is the frequency of A♯4?

A♯4 is 466.16 Hz in equal temperament with A4 = 440 Hz. It is MIDI note 70.

How many A♯ notes are on an 88-key piano?

An 88-key piano runs from A0 to C8 and contains 8 A♯ notes, from A♯0 (29.14 Hz) to A♯7 (3729.31 Hz).

What MIDI number is A♯4?

A♯4 is MIDI note 70. MIDI note numbers run from 0 (C−1) to 127 (G9), with middle C (C4) at 60 and A4 at 69.

Why does the frequency double every octave?

An octave is a 2:1 frequency ratio. In twelve-tone equal temperament the octave is divided into twelve equal steps, so each semitone multiplies the frequency by the twelfth root of two (about 1.0595). Twelve of those steps multiply out to exactly 2.

A♯ Note Frequency (A sharp / B♭) — A♯0 to A♯7

A♯ and B♭ are the same sound. B♭ is much the more common spelling: clarinet, trumpet and tenor sax are transposing instruments in B♭, so their written C sounds as B♭.

Every A♯ on an 88-key piano

Frequencies use equal temperament with A4 = 440 Hz. Range shown: A♯0 to A♯7 — 8 of the 88 keys.

Note	MIDI number	Frequency (Hz)
A♯0	22	29.14
A♯1	34	58.27
A♯2	46	116.54
A♯3	58	233.08
A♯4	70	466.16
A♯5	82	932.33
A♯6	94	1864.66
A♯7	106	3729.31

How the frequency of A sharp is calculated

Modern instruments use twelve-tone equal temperament, where an octave is split into twelve equal semitones. With A4 fixed at 440 Hz, any note’s frequency is:

f = 440 × 2^{(m − 69) / 12}

where m is the MIDI note number. For A♯4 that is m = 70, giving 466.16 Hz.

A♯ and its neighbours

Each semitone changes the frequency by a ratio of 2^1/12 ≈ 1.0595 — about 5.95%. Going up one octave doubles it. So A♯4 at 466.16 Hz has a neighbour 440.00 Hz a semitone below and 493.88 Hz a semitone above, and A♯5 at 932.33 Hz an octave above.

Is A♯ the same as B♭?

Yes — A♯ and B♭ are enharmonically equal: identical pitch, different spelling. On a piano they are the same black key, and on an equal-tempered instrument A♯4 sounds at 466.16 Hz either way. Composers choose the spelling to keep the notation readable in a given key.

Frequently asked questions

What is the frequency of A♯4?: A♯4 is 466.16 Hz in equal temperament with A4 = 440 Hz. It is MIDI note 70.
How many A♯ notes are on an 88-key piano?: An 88-key piano runs from A0 to C8 and contains 8 A♯ notes, from A♯0 (29.14 Hz) to A♯7 (3729.31 Hz).
What MIDI number is A♯4?: A♯4 is MIDI note 70. MIDI note numbers run from 0 (C−1) to 127 (G9), with middle C (C4) at 60 and A4 at 69.
Is A♯ the same as B♭?: Yes. A♯ and B♭ are enharmonic — the same pitch under two names, and the same key on a piano. A♯4 is 466.16 Hz either way.
Why does the frequency double every octave?: An octave is a 2:1 frequency ratio. In twelve-tone equal temperament the octave is divided into twelve equal steps, so each semitone multiplies the frequency by the twelfth root of two (about 1.0595). Twelve of those steps multiply out to exactly 2.

Last updated: 2026-09-01