Note Frequency Calculator

Convert between MIDI note number, note name (A4, C#5, Bb3, F♯4), frequency in Hz, and signed cents deviation. The math is 12-tone equal temperament with A4 = 440 Hz, the standard that virtually every digital synth, MIDI file, and audio engine uses. Type any one of the four representations and the other three update live. Click any key on the piano roll or any row in the reference table to snap the calculator to that note. Pure client-side, offline.

Note — —
MIDI —
Frequency —
Cents off 12-TET —

Piano roll

One octave of keys. White keys are the naturals, black keys are the sharps / flats. Click any key to set the calculator to that note. The active note is highlighted in ; the previous note is .

Reference table

The full chromatic scale for the octave starting at the selected MIDI. Click any row to load that note.

60 = C4 (middle C). 21 = A0, 108 = C8.
Note MIDI Frequency 12-TET ratio to A4

How the math works

In 12-tone equal temperament, every note is 21/12 times the frequency of the note a semitone below it. Working back from the reference pitch A4 = 440 Hz (MIDI 69), the frequency of any other note is f = 440 · 2(m − 69) / 12 where m is the MIDI note number. One semitone is exactly 100 cents, so the offset between any two frequencies is 1200 · log2(f2 / f1) cents.

The standard reference is A4 = 440 Hz, but some ensembles (and a long-running internet argument) prefer 432 Hz. Changing the Reference (A4) input retunes the whole page without breaking the relative pitch math — every frequency shifts by the same ratio, and every interval stays intact.

We deliberately do not model just intonation, Pythagorean tuning, meantone, or microtonal systems (24-TET, 31-EDO, …). Cents deviation is the only escape hatch for non-12-TET pitches: type the exact frequency in Hz and the cents readout will show the offset to the nearest equal-tempered note.