Note Frequency Calculator
| Note | Hz | The landmark |
|---|---|---|
| A0 | 27.50 | bottom of the piano |
| C4 | 261.63 | middle C |
| A4 | 440.00 | the tuning standard |
| A5 | 880.00 | the octave - exactly double |
| C8 | 4186.01 | top of the piano |
Type a note - A4, C#3, F5 - and the converter lands its exact frequency in equal temperament, the tuning modern instruments agree on: twelve equal semitones per octave, with A above middle C pinned at 440 Hz. Type a frequency and the note comes back, cents deviation included.
The arithmetic is one formula: multiply 440 by two to the power of semitones-away-from-A4 over twelve. That single rule builds every pitch Western music uses - the octave table below runs it from the bottom of a piano to the top, and the FAQs cover what happens when an orchestra tunes to something other than 440.
How to use
- Type the note name with its octave - A4, C#3, Bb5 - and the frequency appears in hertz, or run the reverse from a measured frequency.
- The cents field tells you how far off a tuning reading sits: 100 cents is one semitone, and tuners speak in cents because ears hear ratios, not hertz.
- For ensembles tuned to A415 or A442, set the reference pitch first - the whole table shifts with it.
Frequently asked questions
What frequency is A4?
440 hertz by the international standard - the A above middle C, the pitch every orchestra tunes to before a concert. It was not always so: baroque ensembles play near 415, some European orchestras push to 442 or 443 for brightness, and the 1939 London conference that settled on 440 was only ratified as ISO 16 in 1955. Set the reference and every other note follows the same twelve-semitone ladder.
How does the note-to-frequency formula work?
Equal temperament multiplies 440 by two to the power of n over twelve, where n is the signed semitone distance from A4: C#4 is one semitone up (466.16 Hz), G4 sits two semitones down (392.00 Hz), and A5 twelve up lands at 880 Hz - the octave, exactly double. The twelfth root of two, about 1.0595, is the multiplier per semitone, and composing it twelve times lands the octave exactly.
What are cents?
Hundredths of a semitone - the log-scale unit tuners and ears prefer, because pitch perception is ratio-based: one hundred cents is one semitone, twelve hundred an octave. A piano a few cents flat is inaudible to most listeners; twenty cents is audibly out of tune. When a measured frequency falls between notes, the cents readout says which note it is nearest and how far.
Why is C4 middle C and not C1?
Scientific pitch notation numbers octaves from C, and middle C - the one between the bass and treble staves - is the fourth C from the bottom of the piano, hence C4 (261.63 Hz). Confusingly, MIDI calls it note 60 but some manufacturers label it C3; this converter uses the scientific convention throughout, which is what physics and most modern software assume.
Do real instruments actually hit these frequencies?
Approximately, and on purpose: equal temperament is a compromise that makes every key equally usable by making every fifth very slightly narrow. String players and a cappella singers drift toward just intonation - purer ratios like 3:2 - by ear, so a sustained chord lands a few cents off the table. Synthesizers and digital tuners live on these exact numbers; humans approximate them beautifully.