Note Frequencies: C0 to B8 in Hz

How note frequencies work

Modern Western music divides each octave into 12 equal semitones — a system called equal temperament. Every note's frequency follows a single formula:

f = 440 × 2^{(n − 69) / 12}

Here n is the note's MIDI number — simply a count of semitones, where C0 is 12, middle C (C4) is 60, and A4, the tuning reference, is 69. Plug in any number and you get the exact pitch in hertz. That is how the chart above was generated, and it is the same math running inside every digital tuner, including our free online chromatic tuner.

The elegant part is octave doubling: moving up one octave multiplies the frequency by exactly 2. A2 is 110 Hz, A3 is 220 Hz, A4 is 440 Hz, A5 is 880 Hz. Because our ears judge pitch by ratios rather than absolute differences, each doubling sounds like "the same note, only higher."

A short history of concert pitch

A4 = 440 Hz feels like a law of nature, but it is a convention. In the baroque era, ensembles commonly tuned near A = 415 Hz — roughly a semitone below today's standard — and pitch varied from city to city. An international conference fixed A4 at 440 Hz in 1939, later codified as ISO 16, and that is what almost every tuner and keyboard uses now. Some European orchestras tune slightly sharp, at 442–443 Hz, for a marginally brighter sound. The A4 selector above lets you see exactly what any of these references does to every note.

Anchors worth memorizing

• Bass low E = E1 = 41.20 Hz
• Guitar low E = E2 = 82.41 Hz
• Middle C = C4 = 261.63 Hz
• Violin E string = E5 = 659.26 Hz

To check your own instrument against these numbers, open the online tuner in your browser — or take it with you: our free iOS app Tuner: Guitar, Violin & Bass turns the screen green when you are in tune and lets you adjust the A4 reference. And remember that pitch is only half of good playing; the online metronome covers the other half.