A4 Frequency – Complete Guide

A4 has a frequency of 440 Hz under the standard A440 tuning reference. It is the A above middle C, and 440 Hz means that its sound wave completes 440 vibration cycles per second.

Musicians also call A4 “concert A” because orchestras and other ensembles commonly use it as their shared tuning note. If you want to see how it relates to other pitches, a musical note frequency chart places A4 within the wider keyboard and audible spectrum.

What Is the Frequency of A4?

The standard frequency of A4 is exactly 440 Hz. Hertz measures cycles per second, so an ideal 440 Hz tone repeats its waveform 440 times every second. One cycle lasts about 0.00227 seconds, or 2.27 milliseconds.

The International Organization for Standardization defines A4 = 440 Hz in ISO 16. This gives instrument makers and performers a common reference. A real A4 is more complex than a pure sine wave: it normally contains a 440 Hz fundamental plus harmonics.

Where Is A4 on a Piano and Musical Staff?

A4 is the A immediately above middle C, or C4. On an 88-key piano, it is the 49th key when counted from the lowest key, A0. In treble clef, A4 sits in the second space from the bottom of the staff.

Middle C is approximately 261.63 Hz in A440 equal temperament. Moving from C4 to A4 covers nine semitones. The frequency of C4 provides a useful landmark when locating concert A by sound or on a keyboard.

Why Is It Called A4 Rather Than A440?

“A4” is a scientific pitch notation label: A identifies the note class, while 4 identifies the octave. “A440” describes a tuning standard in which A4 is assigned 440 Hz. These expressions are related, but they do not mean exactly the same thing.

The octave number matters because there are many notes named A. A3 is 220 Hz, while A5 is 880 Hz. Without an octave number, “A” does not identify one exact register.

Why Is A4 Tuned to 440 Hz?

A4 is tuned to 440 Hz because musicians need an agreed reference before playing together. Other notes can then be tuned relative to it. A440 became an international standard after pitch levels had varied by location and era.

What Does the A440 Standard Mean?

The A440 standard assigns 440 Hz to A4. It does not mean that every sound is 440 Hz or specify every detail of a tuning system. Most modern Western instruments use 12-tone equal temperament to determine the remaining frequencies.

The standard is widely used, but an orchestra can deliberately agree on another value. The broader explanation of concert-pitch reference standards shows why ensemble agreement matters more than assuming every performance uses the same setting.

How Do Musicians Use Concert A?

An orchestra commonly tunes to an A sounded by the oboe or another agreed source. String players adjust their A strings first, then tune the remaining strings. Fixed-pitch instruments must already be prepared for the chosen reference.

Electronic tuners often display a 440, 442, or 443 Hz calibration setting. Check it before tuning; two accurate tuners set differently will indicate different targets.

How Do You Calculate Frequencies From A4?

In 12-tone equal temperament, calculate any note relative to A4 with:

[
f = 440 \times 2^{n/12}
]

Here, (f) is frequency in hertz and (n) is the number of semitones above or below A4. Use a positive value above A4 and a negative value below it. Each 12-semitone change doubles or halves the frequency.

Frequencies of A Across the Piano

Note	Frequency
A0	27.50 Hz
A1	55.00 Hz
A2	110.00 Hz
A3	220.00 Hz
A4	440.00 Hz
A5	880.00 Hz
A6	1760.00 Hz
A7	3520.00 Hz

This doubling pattern explains the relationship between octaves. The pitches sound higher or lower but retain the same note name. An explanation of how octave equivalence works connects that ratio with perception.

Frequencies of Notes Near A4

Note	Semitones from A4	Frequency
F4	-4	349.23 Hz
F♯4/G♭4	-3	369.99 Hz
G4	-2	392.00 Hz
G♯4/A♭4	-1	415.30 Hz
A4	0	440.00 Hz
A♯4/B♭4	+1	466.16 Hz
B4	+2	493.88 Hz
C5	+3	523.25 Hz

For G4, (n=-2), so (440 \times 2^{-2/12}) gives 392.00 Hz. For C5, (n=3), so (440 \times 2^{3/12}) gives 523.25 Hz. Equal-tempered semitones therefore use a constant ratio, not a fixed number of hertz.

Is A4 Always 440 Hz?

A4 is 440 Hz under A440, but the note can be assigned another reference frequency. An ensemble may use a higher modern orchestral pitch or lower historical pitch. Players remain in tune when every instrument follows the same reference.

Reference	Typical context	Difference from A440
A415	Historically informed Baroque performance	About one equal-tempered semitone lower
A432	Alternative modern reference	About 31.8 cents lower
A440	International standard	0 cents
A442	Some modern orchestras	About 7.9 cents higher
A443	Some modern orchestras	About 11.8 cents higher

A cent is one hundredth of an equal-tempered semitone. These differences shift every note, not only A4. The comparison of 432 Hz and 440 Hz tuning explains the measurable change without unsupported claims about universal healing properties.

Modern Orchestral and Historical Pitch

Some orchestras choose A442 or A443 to match local practice. Historically informed groups often use A415 for Baroque repertoire, although historical pitch was not one universal value.

The note remains A4 in each case. Its notation indicates musical position; the agreed reference determines its physical frequency. This distinction prevents the common mistake of treating “A4” and “440 Hz” as permanently interchangeable in every tuning context.

How Can You Recognize or Tune to A4?

To tune to A4, play a verified reference and adjust your voice or instrument until the pitches match. Listen for pulsing, called beats, when sustained tones are close but unequal. Beats slow as the frequencies converge.

Match A4 With a Voice or Instrument

Listen first, imagine the pitch internally, and then produce it comfortably. Singers should not force A4 outside their current range. Instrument players should make small adjustments and replay the note.

A pitch detector can indicate whether a sound is sharp or flat, but a browser reading is an estimate. Noise, microphone response, harmonics, note attacks, and vibrato can make it fluctuate. The distinction between physical frequency and perceived pitch explains why musical tones are not perfectly steady laboratory signals.

Check Whether the Note Is Sharp or Flat

A reading above the selected reference is sharp; one below it is flat. At A440, 441 Hz is about 3.9 cents sharp and 439 Hz is about 3.9 cents flat. Evaluate a sustained note after its initial attack rather than judging the first unstable instant.

When tuning strings, approach the target carefully and recheck after adjusting the others. One pass may not finish the job. For focused practice, learn how to recognize a 440 Hz note by comparing it with neighboring pitches.

Frequently Asked Questions

Is A4 the same as 440 Hz?

A4 equals 440 Hz when the A440 reference is used. A4 is the note label, while 440 Hz is the frequency assigned to it under that standard.

Is A4 above or below middle C?

A4 is above middle C. Middle C is C4, and A4 lies nine semitones higher.

What are the frequencies of A3 and A5?

In A440 tuning, A3 is 220 Hz and A5 is 880 Hz. Each octave down halves frequency, while each octave up doubles it.

Can A4 be tuned to 432 Hz?

Yes. Under an A432 reference, A4 is set to 432 Hz and all other notes are tuned relative to it. This is an alternative reference rather than the ISO A440 standard.

Why do orchestras sometimes tune A4 to 442 Hz?

Some orchestras use A442 because of regional tradition, ensemble preference, or the pitch design of their instruments and performance venues. A442 is only about 7.9 cents above A440, far less than one semitone.

Is 440 Hz a pure tone or a complete musical sound?

440 Hz can describe a pure sine tone, but an A4 from a real voice or instrument usually contains a 440 Hz fundamental plus harmonics and noise components. Those additional frequencies help determine the sound’s timbre without changing its basic note identity.