Note Frequency Reference

What this tool does

This note frequency reference converts between musical note names and their frequencies in hertz. Pick a note and an octave — A4, middle C, F sharp 2, anything you like — and the tool shows its exact frequency in equal temperament, along with its MIDI note number. A reverse mode does the opposite: type in a frequency and it returns the nearest note plus how many cents sharp or flat your value is. You can play any tone through your speakers to hear it, and a full reference table lists every note across seven octaves.

The reference pitch is adjustable. The standard A4 = 440 Hz is the default, but you can move it anywhere from 390 to 480 Hz to match an orchestra that tunes high, a period ensemble that tunes low, or any other pitch standard. Every figure recalculates the moment you change it.

When you would use it

Instrument builders, repairers and tuners need exact target frequencies to set strings, reeds, bars and pipes. Audio engineers and synthesizer programmers look up frequencies to tune oscillators, place filters and identify the pitch of a hum or a resonance. Students and teachers use it to understand how the mathematics of equal temperament produces the notes we hear, and to check that a note they have calculated by hand is right. Anyone working with electronic tones — testing speakers, generating reference pitches, calibrating a tuner — reaches for a table like this. Reverse mode is handy when a piece of software or a measurement gives you a raw frequency and you want to know which note it is closest to.

How to use it

1. Choose the lookup direction: note to frequency, or frequency to note.
2. Set the reference pitch if you are not using the standard 440 Hz — most users can leave it alone.
3. In note mode, pick a note name and an octave. The frequency, in hertz, appears immediately.
4. In frequency mode, type a frequency in hertz. The nearest note and the cents offset appear.
5. Press Play tone to hear the pitch through your speakers or headphones.
6. Scroll the reference table to compare frequencies across all seven octaves; your current selection is highlighted.

How it works

Equal temperament splits the octave into twelve equal semitones. Each semitone multiplies the frequency by the twelfth root of two — about 1.0595 — so a note twelve semitones up is exactly double the frequency, one octave higher. Every note’s frequency is therefore the reference pitch multiplied by two raised to the number of semitones from A4, divided by twelve. Octaves in scientific pitch notation are numbered so that middle C is C4 and the reference A is A4. The reverse calculation runs the formula backwards with a logarithm to find how many semitones — and how many leftover cents — a frequency lies from the reference.

To tune a real instrument to these targets by ear, use the guitar tuner. To see which notes form a scale, the piano scale reference lays them out on a keyboard, and the metronome and drum practice click keep your practice in time. The Pomodoro timer helps structure longer sessions, and the audio trimmer edits clips in the browser.

Privacy

Every conversion here is arithmetic carried out by JavaScript in your browser. Nothing you enter — no note, no frequency, no reference pitch — is uploaded, logged or stored between visits. The tones you play are generated locally by the Web Audio API; the tool never opens your microphone. Closing the tab clears all input, and because the maths and the data are bundled into the page, the reference works fully offline once loaded. It runs entirely on your own device.