Music tools
Note, frequency and MIDI converter
Convert between note name, frequency, and MIDI number, with an adjustable A4 reference. Everything runs in your browser.
| Note | Frequency (Hz) | MIDI |
|---|
How it works
Convert freely between the three ways of naming a pitch: the note name (like A4), its frequency in hertz, and its MIDI note number. Type into any field and the other two follow, using equal temperament. The reference pitch A4 defaults to 440 Hz but you can change it - to 432 Hz, 442 Hz, or anything else - and the whole mapping shifts with it.
A reference table lists every note from the low end to the top of the range with its frequency and MIDI number, so you can scan for the value you need. The conversion is pure arithmetic done in your browser: each semitone is a factor of the twelfth root of two, and MIDI number 69 is defined as A4. Nothing is uploaded.
Example. With A4 at 440 Hz, entering the note A4 shows 440 Hz and MIDI 69; typing 261.63 Hz resolves to C4 (MIDI 60); entering MIDI 81 gives A5 at 880 Hz, exactly one octave up.
FAQ
How is a note converted to a frequency?
Equal temperament sets each semitone a factor of 2^(1/12) apart. From the reference A4, a note that is n semitones away has frequency A4 x 2^(n/12). With A4 at 440 Hz, that gives the standard pitches.
What is the MIDI note number?
MIDI numbers each pitch with an integer from 0 to 127, where 69 is A4. Each step of one is a semitone, so middle C (C4) is 60. The converter shows this number alongside the note name and frequency.
Can I use a reference pitch other than 440 Hz?
Yes. Change the A4 value to 432, 442, or any frequency and every conversion and the reference table update to match, so you can work in whatever tuning standard you need.
Does this run offline?
Yes. The conversions are plain math computed in your browser with no server calls, so the tool works offline and nothing is uploaded.