A (musical note)

${ \new Staff \with{ \magnifyStaff #3/2 } << \time 2/1 \override Score.TimeSignature #'stencil = ##f { \clef bass a1_A \clef treble a'_A } >> }$

A is a musical note equivalent to 440 Hz in typical A440 tuning. It is the sixth note of La and the tenth semitone of the fixed-do solfège.

Its enharmonic equivalents are B (B double-flat) and G (G double-sharp).

"A" is generally used as a standard for tuning. When the orchestra tunes, the oboe plays an "A" and the rest of the instruments tune to match that pitch. Every string instrument in the orchestra has an A string, from which each player can tune the rest of their instrument.

"A" is also used in combination with a number (e.g. A-440) to label the pitch standard. The number designates the frequency in hertz. A lower number indicates a lower pitch.

The International Standards Organization (ISO) has standardized the pitch at A-440.^[1] However, tuning has varied over time, geographical region, or instrument maker. In 17th-century Europe, tunings ranged from about A-374 to A-403, approximately two to three semitones below A-440. Historical examples exist of instruments, tuning forks, or standards ranging from A-309 to A-455.3,^[2] a difference of almost six semitones. Although the official standard today is A-440, some orchestral groups and chamber groups prefer to tune a little higher, at A-442 or even A-444. Baroque pitch is usually cited as A-415, which is a semitone lower than modern pitch.

A₀ is the lowest note on standard pianos with 88 keys, and the rarer older 85-key pianos.

Designation by octave

Scientific designation	Helmholtz designation	Octave name	Frequency (Hz)	MIDI note number
A₋₁	A,,, or ,,,A or AAAA	Subsubcontra	13.75	9
A₀	A,, or ,,A or AAA	Subcontra	27.5	21
A₁	A, or ,A or AA	Contra	55	33
A₂	A	Great	110	45
A₃	a	Small	220	57
A₄	a′	One-lined	440	69
A₅	a′′	Two-lined	880	81
A₆	a′′′	Three-lined	1760	93
A₇	a′′′′	Four-lined	3520	105
A₈	a′′′′′	Five-lined	7040	117
A₉	a′′′′′′	Six-lined	14080	N/A
A₁₀	a′′′′′′′	Seven-lined	28160	N/A