Why does the octave number change at C rather than at A?

Because scientific pitch notation labels the whole run of notes from C upward with the same octave number, so middle C is C4 and the B above it is B4 while the A below is A3. It is a convention rather than a consequence of the arithmetic, but it is the one every instrument and score follows.

What does the reference slider actually do?

It scales the whole set of notes by the ratio between your chosen reference and four hundred and forty. Because equal temperament defines every note relative to the reference, moving it shifts every note proportionally rather than adding a fixed number of hertz, which is exactly how tuning to an older pitch works.

Can I enter a note number between two integers for a detuned pitch?

The field is whole numbers only, since the point of the tool is the mapping between note numbers and names. For a pitch that sits between two notes, work in hertz with the frequency to MIDI note tool, which reports the exact fractional position along with the offset in cents.

Why is A4 note number sixty nine?

Because the numbering starts at zero for the lowest note in the range and counts upward in semitones, and sixty nine semitones above that starting point lands on A4. The starting note itself is far below the range of hearing, which is why the low numbers are seldom used in practice.

Does the result depend on any audio settings?

No. Nothing is measured and nothing is played; the frequency is computed from the note number and the reference alone. That also means the figure is exact rather than an estimate, and it holds whatever hardware or file it is later applied to.

MIDI Note to Frequency

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MIDI Note to Frequency converts a note number into the frequency it sounds at, with the tuning reference adjustable. It also shows the twelve notes around the one you entered for context.

What is MIDI Note to Frequency?

Enter a note number from zero to one hundred and twenty seven and read its name, its frequency, and the twelve notes around it.

The controls and output:

A note number field from zero to one hundred and twenty seven, defaulting to sixty nine, which is the note A4 at the standard reference.
A tuning reference slider for the note A4 from four hundred and fifteen to four hundred and sixty six hertz, defaulting to the standard four hundred and forty.
A large readout giving the frequency to two decimal places along with the note name and the reference in use.
A table of twelve note numbers centred on the one entered, each with its note name and frequency, so the neighbourhood can be read at a glance.

The conversion uses the MIDI numbering scheme together with equal temperament. Every note number is a semitone apart, and each semitone is a fixed ratio rather than a fixed number of hertz, so the whole scale can be generated from a single anchor point by multiplying by the twelfth root of two repeatedly. That anchor is the reference: the tool takes the standard relationship and then scales the whole result by the ratio between your reference and four hundred and forty, which means moving the slider shifts every note proportionally rather than transposing the keyboard. The note name is derived from the number itself, with the letter repeating every twelve numbers and the octave number incrementing at C rather than at A, which is the convention that most often catches people out. The table is there because a note number in isolation is hard to place: seeing that sixty nine is A4, that the note below is G sharp and the one above is A sharp, and what each of them sounds at, is usually enough to confirm that the number entered was the one intended. The whole thing is arithmetic on a single reference, so nothing needs measuring and nothing depends on any audio.

What it does not do:

No decimal note numbers, so a detuned pitch is a matter for the other direction or for the cents calculator.
No temperament other than equal, so a just or historically tempered scale differs from the result.
No MIDI file reading, so a sequence has to be looked up note by note.
No instrument transposition, so a written note for a transposing instrument is not converted.
No audio, and nothing is played back.
Nothing is uploaded, and no history is kept.

Use it when a sequence or a controller sends note numbers and the question is what they sound like, when a synthesizer has to be tuned to match another instrument in hertz, or when the reference itself is in doubt. When the input is a frequency and the question is the other way round, the frequency to MIDI note tool gives the nearest note plus the offset, and when a note name rather than a number is the starting point, the note frequency calculator accepts names as typed.

How to use MIDI Note to Frequency

Enter the MIDI note number, using sixty nine as a familiar starting point.
Read the note name and frequency, and check the reference the result assumes.
Move the reference slider if the material is not at modern pitch.
Use the table of twelve notes to confirm where the note sits in its neighbourhood.

When to use MIDI Note to Frequency vs related tools

MIDI Note to Frequency is the tool for turning a note number into hertz, which is what a sequencer or controller speaks in. Frequency to MIDI Note works in the opposite direction and adds the detuning, and Note Frequency Calculator accepts a written note name instead of a number. When the detuning rather than the note is the question, Cents Calculator works directly in that unit.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.