About Note to Frequency
Note to Frequency gives the pitch of a musical note in hertz, using the standard equal-temperament tuning in which A4 is set to 440 Hz. Choose a note such as C4 or F#5 and it returns its frequency to two decimal places — the figure you need to set a synthesiser oscillator, tune a sample or check an instrument against a reference.
The calculation places each note on the MIDI number line and applies the equal-temperament formula, in which every semitone multiplies the frequency by the twelfth root of two. That is why the ratios between notes are not round numbers except at the octave: twelve semitone steps together double the frequency exactly, so A4 at 440 Hz and A5 at 880 Hz sit an octave apart with eleven unevenly spaced steps in between.
The note list spans three octaves, from C3 up to B5, which covers the great majority of melodic and harmonic material. Notes outside that range are not offered, so for very low or very high registers you would work from the MIDI conversion tools instead.
The lookup is one-directional and returns a single figure. There is no reverse field on the page where a frequency could be entered to find the matching note, so identifying an unknown pitch means using a different tool. What comes back is the frequency alone: the MIDI number, the note's position in the scale, its cents deviation from any other reference and the wavelength at that pitch are all omitted, and no cents-offset or alternative tuning can be applied — the whole table is locked to the standard reference pitch, so a piece written for an orchestra tuning a few hertz higher cannot be accommodated. Nothing can be entered by name either, so a note written in the German convention where B means what English calls B flat would be selected by the wrong entry in the list.
How to use Note to Frequency
- 1 Pick the note you want from the dropdown — C3 through B5 are available.
- 2 Run the tool to see the frequency in hertz.
- 3 Use the figure to tune an oscillator or compare against a reference tone.
Frequently asked questions
What tuning standard does this use?
Equal temperament with A4 at 440 Hz, the international standard pitch. Every other note is derived from that reference by the equal-temperament formula, so the whole scale is internally consistent.
Why is an octave exactly double the frequency?
Because that is how equal temperament is constructed. Twelve semitone steps each multiply the frequency by the twelfth root of two, and twelve of those multiplications together give exactly two. So A5 is precisely twice A4.
Can I look up a note outside C3 to B5?
Not from this dropdown — the list deliberately covers three octaves, which is enough for most work. For extreme registers, use the MIDI to Frequency tool, which accepts the full 0 to 127 MIDI range.
Why are the frequencies not whole numbers?
Because equal temperament divides the octave into twelve equal ratios rather than whole-number relationships. Only the octaves land on neat multiples; the notes between them sit on irrational ratios and therefore produce decimal frequencies.
Free, online, and private
Free to use
Note to Frequency is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How Note to Frequency behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Options | 36 — the twelve pitch classes C, C#, D, D#, E, F, F#, G, G#, A, A# and B across octaves 3, 4 and 5 |
| Input | a single note select box, default A4 |
| Tuning | twelve-tone equal temperament from A4 = 440 Hz: 440 × 2^((MIDI − 69) ÷ 12) |
| MIDI derivation | MIDI = (octave + 1) × 12 + the note index in the C-to-B list, so A4 lands on 69 |
| Output | the note name followed by its frequency to two decimals — A4 = 440.00 Hz, C4 = 261.63 Hz, C5 = 523.25 Hz |
Compiled from the implementation of this tool and checked against it by itoolnet.
What Note to Frequency does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- Three octaves is the whole range. The list runs from C3 to B5, so a bass note such as E1 or a high C7 cannot be selected, and there is no free-text box or MIDI-number entry to reach anything outside it.
- Every pitch class has exactly one spelling, and it is the sharp. D flat has to be read as C sharp, no flat notation is offered and no enharmonic pair is recognised, so a score written in a flat key will not line up with the names in the list.
- Frequencies are theoretical equal-temperament values from a 440 Hz reference. There is no alternate concert pitch such as A = 415 or 442 Hz, no just-intonation ratios, no cents offset and no stretched-octave tuning, so nothing here models a real instrument far from the reference.
Tested and documented by itoolnet, the team that builds and maintains this site.