440 Hz is the note A4 in scientific pitch notation. It is the A above middle C and is commonly called A440, concert A, or the standard tuning pitch. The number means that the sound wave completes 440 cycles per second.
That answer assumes the tuning reference A4 = 440 Hz. Hertz measures physical frequency, while a note name describes pitch within a tuning and notation system. This guide to pitch and frequency explains the distinction.
What Note Is 440 Hz?
In standard twelve-tone equal temperament, 440 Hz corresponds exactly to A4. On a piano, A4 is the A immediately above middle C, which is C4. It is the 49th key from the left on a standard 88-key piano.
What does 440 Hz mean?
Hertz, abbreviated Hz, measures cycles per second. A steady 440 Hz tone creates 440 pressure-wave cycles each second, and the ear usually perceives its fundamental pitch as A4. The broader explanation of what hertz means in music connects this measurement to notes, octaves, and sound waves.
A musical sound rarely contains one frequency alone. A violin, guitar, piano, or voice producing A4 usually has a 440 Hz fundamental plus higher harmonics. These help two instruments playing the same A4 sound different.
Is 440 Hz the same as middle C?
No. Middle C is C4, approximately 261.63 Hz when A4 is set to 440 Hz. A4 sits nine semitones above middle C and sounds noticeably higher. The two pitches are useful landmarks, but they are not alternate names for the same note.
Its frequency and staff position are covered in this guide to middle C and its frequency.
Why Is 440 Hz Called A4?
The “A” identifies the note, while the “4” identifies its octave in scientific pitch notation. Under this system, middle C begins octave 4, so the A above it is A4. The next A up is A5, and the next A down is A3.
Why might software label 440 Hz as A3?
Some software uses a different octave-numbering convention and displays 440 Hz as A3 even though the pitch has not changed. Most contemporary music references label it A4.
When labels disagree, check how the program names middle C. If it uses C3, it will probably use A3 for 440 Hz. This guide to scientific pitch notation helps translate between systems.
Where is A4 written and played?
In treble clef, A4 appears in the second space from the bottom. On a standard piano, it is the A above middle C. Orchestras commonly use an A near this pitch as a shared reference because string instruments have open A strings and many orchestral instruments can produce the note clearly.
ISO 16 specifies 440 Hz as the standard reference frequency for A on the treble staff. Musicians can tune independently and still play at compatible pitches, although an ensemble may agree on another reference.
What Notes Are Above and Below 440 Hz?
The chromatic neighbors of A4 are G-sharp 4/A-flat 4 below it and A-sharp 4/B-flat 4 above it. In twelve-tone equal temperament, each semitone changes frequency by the twelfth root of 2.
| Position | Note | Frequency |
|---|---|---|
| One semitone below | G♯4/A♭4 | 415.30 Hz |
| Reference pitch | A4 | 440.00 Hz |
| One semitone above | A♯4/B♭4 | 466.16 Hz |
Values are rounded to two decimal places. A music-note frequency chart shows the relationship across the chromatic scale.
What happens to A in other octaves?
Moving up one octave doubles frequency; moving down one octave halves it. The note letter remains A because the pitches belong to the same pitch class, but the octave number changes.
| Note | Relationship to A4 | Frequency |
| A2 | Two octaves below | 110 Hz |
| A3 | One octave below | 220 Hz |
| A4 | Reference A | 440 Hz |
| A5 | One octave above | 880 Hz |
| A6 | Two octaves above | 1,760 Hz |
This doubling rule applies to every note, not only A. The underlying relationship is explained in the guide to how octaves work.
How are other note frequencies calculated?
In equal temperament, the frequency of a note can be calculated from A4 with:
frequency = 440 × 2^(n/12)
Here, n is the number of semitones above or below A4. Positive values move upward; negative values move downward. For example, A5 is 12 semitones above A4, so its frequency is 440 × 2^(12/12) = 880 Hz.
Is 440 Hz Always the Note A?
440 Hz is exactly A4 only when the tuning reference defines A4 as 440 Hz. If an ensemble tunes A4 to 442 Hz, a 440 Hz tone is about 7.9 cents flat relative to its chosen A4. It will still be heard and usually identified as an A, but it is not the ensemble’s precisely tuned A4.
What changes with 432 Hz tuning?
When A4 is defined as 432 Hz, a literal 440 Hz tone is about 31.8 cents sharp of A4. It remains closer to A4 than to either neighboring chromatic note, but it no longer matches the selected reference exactly.
This is why “A4” and “440 Hz” should not be treated as universally identical labels. A4 is a musical note position; 440 Hz is a fixed physical frequency. The comparison of 432 Hz and 440 Hz tuning explores what changes—and what does not—when the reference pitch moves.
Myth versus reality
Myth: 440 Hz is the only correct frequency for A4.
Reality: 440 Hz is the international standard reference and the most common modern default, but some orchestras, historical-performance groups, and individual musicians use another agreed reference. Successful ensemble tuning depends on everyone using the same reference, not on treating every alternative as an error.
How Can You Identify or Match a 440 Hz Tone?
You can identify 440 Hz with a chromatic tuner or pitch detector, which should display A4 when its calibration is set to A = 440 Hz. A browser or microphone reading is an estimate: room noise, harmonics, microphone quality, and an unstable sound source can cause the display to fluctuate.
Match concert A with a tuner
Play or sing a steady tone, keep the microphone at a consistent distance, and watch both the note name and cents indicator. Aim for A4 with the deviation centered near zero cents. If the tuner has a calibration setting, confirm that it reads 440 Hz before interpreting the result.
Learning how to identify musical notes can help you separate pitch matching from note naming. Matching means reproducing the sound; identification means recognizing it as A without being told.
Match 440 Hz by ear
Listen to a reliable A4 reference, pause it, then sing or play the note back. Alternate between the reference and your sound. A pulsing or “beating” sensation often becomes slower as two sustained pitches approach each other, although timbre and tuning stability can make the comparison harder.
Practice can build relative-pitch memory, but recognizing A4 without a reference is associated with absolute pitch.
Frequently Asked Questions
Is 440 Hz A3 or A4?
440 Hz is A4 in scientific pitch notation, the convention used by most modern music references. Some software calls it A3 because it numbers octaves differently, but the audible frequency remains unchanged.
What are the frequencies of A3 and A5?
A3 is 220 Hz, and A5 is 880 Hz when A4 equals 440 Hz. Each octave down halves frequency, while each octave up doubles it.
What note is 432 Hz when A4 equals 440 Hz?
With A4 calibrated to 440 Hz, 432 Hz is an A4 that is approximately 31.8 cents flat. It is not a different chromatic note because it remains much closer to A4 than to G♯4/A♭4.
Is every A note tuned to 440 Hz?
No. Only A4 is 440 Hz under standard tuning. Other A notes occur at octave-related frequencies such as A3 at 220 Hz and A5 at 880 Hz.
Why do orchestras tune to A?
A provides a practical common pitch that orchestral instruments can produce clearly, and string players have an open A string. The tuning note establishes a shared reference; musicians then tune their remaining notes or strings relative to it.
What wavelength does a 440 Hz sound have?
At a sound speed of about 343 metres per second in air, a 440 Hz tone has a wavelength of roughly 0.78 metres. The value changes slightly with air temperature because the speed of sound changes.
Vincent is a pitch detection and vocal analysis writer at OnlinePitchDetector. He focuses on pitch recognition, vocal frequency analysis, singing tools, and real-time audio testing for singers, musicians, producers, and beginners.