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.

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.

What is the MIDI Note Number Converter?

Free MIDI note number converter. Translate between MIDI numbers (0-127), note names with octave (C-1 to G9) and frequency in Hz, with adjustable A4 reference tuning. Essential for MIDI programming, DAWs and synths. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

MIDI Note Number Converter

Name: MIDI Note Number Converter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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 MIDI note numbering works

MIDI numbering is linear in semitones, starting from C in the lowest octave. Two formulas extract the note name and octave from any MIDI number:

note index = midi mod 12      (0=C, 1=C#, 2=D, … 11=B)
octave     = floor(midi / 12) − 1

So MIDI 60 is C in octave 4 (middle C, or C4), and MIDI 69 is A in octave 4 (A4, concert pitch). The full range runs from MIDI 0 (C-1) at approximately 8.18 Hz all the way to MIDI 127 (G9) at approximately 12,543 Hz.

Converting to frequency

The equal-temperament formula anchors every pitch to A4:

frequency = A4_Hz × 2^((midi − 69) / 12)

With A4 at 440 Hz, this places middle C at 261.63 Hz and each octave exactly doubles the frequency. The formula is fully reversible — if you know the frequency, you can find the MIDI number and note name by working backwards.

Quick reference: common MIDI numbers

MIDI	Note	Frequency (A4=440 Hz)	Typical use
21	A0	27.50 Hz	Lowest piano key
36	C2	65.41 Hz	Bass guitar low string
48	C3	130.81 Hz	Cello open C range
60	C4	261.63 Hz	Middle C
69	A4	440.00 Hz	Concert tuning reference
72	C5	523.25 Hz	Violin E-string area
108	C8	4186.01 Hz	Highest piano key area
127	G9	~12,543 Hz	MIDI maximum

The octave numbering debate

The converter uses scientific pitch notation where middle C (MIDI 60) is C4. Some manufacturers — notably older Yamaha instruments — label the same note C3. The MIDI number is always unambiguous; when you need to communicate with someone using different gear, reference the MIDI number rather than the note name.

Alternative tunings

The tool lets you set a custom A4 reference. Change it to 432 Hz and every note shifts proportionally downward: A4 reads 432 Hz, middle C drops to about 256.87 Hz. This is useful for confirming sample pitch when working with period-instrument recordings or alternative tuning systems. Set A4 to 415 Hz to match Baroque pitch, or 466 Hz for high Baroque. All frequencies scale from whatever reference you set.

Converting a note name to MIDI works in reverse: midi = (octave + 1) × 12 + semitone, where sharps and flats are treated as enharmonic equivalents (Db4 = C#4 = MIDI 61).