How does a MIDI note number map to a note?

MIDI defines 128 notes numbered 0 to 127. Number 0 is C-1 and each step up is one semitone. Middle C is MIDI 60 (C4) and A4 is MIDI 69. The note name is the number modulo 12, and the octave is floor(number / 12) minus 1.

How is the frequency calculated from a MIDI number?

The tool uses frequency = A4 · 2^((midi − 69) / 12). With A4 at 440 Hz, MIDI 69 gives 440 Hz, MIDI 60 (middle C) gives about 261.63 Hz, and each octave doubles the frequency. Changing the A4 reference scales every note proportionally.

Why does middle C show as C4 here but C3 elsewhere?

There are competing octave-numbering conventions. This tool uses scientific pitch notation, where middle C (MIDI 60) is C4. Some manufacturers, notably older Yamaha gear, label the same note C3. The MIDI number is unambiguous, so use that when in doubt.

Can I enter flats as well as sharps?

Yes. The note-name input accepts both, so Db3 and C#3 both resolve to the same MIDI number. Output note names are shown using sharps by convention, but the conversion is identical either way since they are enharmonic equivalents.

What is the valid range?

MIDI numbers run from 0 (C-1, about 8.18 Hz) to 127 (G9, about 12 543 Hz at A4 = 440). Values outside 0 to 127, or note names whose octave pushes them out of that range, are rejected because they are not representable in standard MIDI.

MIDI Note Number Converter

MIDI represents every pitch as a whole number from 0 to 127. This converter moves freely between those numbers, human-readable note names (with octave), and the actual frequency in Hz — the three views you constantly switch between when programming synths, editing piano rolls, or mapping samples.

How it works

MIDI numbering is linear in semitones. Note name and octave come straight from the number:

note index = midi mod 12      (0=C, 1=C#, … 11=B)
octave     = floor(midi / 12) − 1

So MIDI 60 is C4 (middle C) and MIDI 69 is A4. The frequency follows the equal-temperament relation anchored at A4:

frequency = A4 · 2^((midi − 69) / 12)

Converting a note name back to a MIDI number reverses this: midi = (octave + 1) · 12 + semitone, where the semitone is looked up from the letter and accidental. Both sharps and flats are accepted on input.

Tips and example

Middle C, MIDI 60, resolves to C4 and 261.63 Hz at standard tuning. Type the note name A4 instead and you get MIDI 69 and exactly 440 Hz. Set the A4 reference to 432 Hz and that same A4 reads 432 Hz while middle C drops to about 256.87 Hz.

Use the MIDI number as the unambiguous identifier when octave labels disagree.
Adjust A4 to match alternative tunings before reading frequencies.
Flats and sharps are interchangeable on input — Db4 equals C#4.

The converter runs entirely in your browser.