Piano Note & Frequency Finder

Look up any note's frequency in Hz and its key number on an 88-key piano, from A0 up to C8.

How it works

Pick a note name and an octave and the calculator tells you three things: the exact frequency in hertz, which of the 88 keys it is, and where that sits on a full-size keyboard. Octaves are numbered using scientific pitch notation, the same system printed in most method books: each octave runs from C up to B, and the number changes at C, not at A. So the A below middle C is A3, not A4, even though it sounds close to middle C. Middle C itself is C4.

Worked example: pick C and octave 4. That's middle C, MIDI note 60, which works out to 261.63 Hz and key 40 of 88, roughly in the middle of the keyboard just to the left of the maker's name plate. Move up to A4 and you land on 440 Hz exactly, the reference pitch that orchestras and tuners around the world use to agree on what "in tune" means. Every other note on the keyboard is defined relative to that one frequency.

The math behind it is equal temperament: each of the 12 keys in an octave (7 white, 5 black) is exactly the same frequency ratio apart from its neighbors, the twelfth root of 2, so every octave doubles the frequency of the one before it. That's why C5 is 523.25 Hz, almost exactly double C4's 261.63 Hz. It's a compromise tuning that makes every key sound acceptably in tune in every key signature, rather than one key sounding perfect and the rest sounding off.

FAQ

Why does the octave number change at C instead of A?

It's just the convention scientific pitch notation settled on, matching how the piano keyboard is laid out in groups starting on C. It can feel backwards at first because A4 (concert pitch) is a well-known reference, but the C before it is already in octave 4, not 3.

Why is A4 the tuning reference and not C4?

There's no acoustic reason it had to be A specifically. It became the international standard (440 Hz) in the 20th century mostly for historical and practical reasons, so that orchestras, piano tuners, and instrument makers worldwide would all agree on one number. Some ensembles tune slightly sharp of it, but 440 Hz is what you'll see on every tuner and metronome app by default.

What does "key 40 of 88" actually tell me?

It counts physical keys from the bottom of the keyboard, starting at A0 as key 1 and ending at C8 as key 88, including both black and white keys. It's mostly useful for checking whether a note fits on a standard 88-key piano at all, since some digital keyboards only cover 61 or 76 keys and cut off the lowest and highest notes.

Does this work for notes below A0 or above C8?

The calculator will still compute a frequency for those notes since the math doesn't care where the keyboard physically ends, but it will flag them as out of range because no standard acoustic or digital piano has those keys.

For more on getting your bearings on the keyboard, see how to find middle C, the names of the piano keys, and how many keys you actually need.