How note frequencies work
In twelve-tone equal temperament, the tuning system almost all modern music uses, each semitone multiplies the frequency by the twelfth root of two (about 1.0595), so every octave exactly doubles it. Everything is anchored to A4, which is 440 Hz by international standard.
The formula: f = 440 × 2(n − 69) / 12, where n is the MIDI note number (A4 = 69, middle C = 60).
Useful reference points
- Middle C (C4): 261.63 Hz
- A4, the tuning note: 440 Hz
- Lowest piano key (A0): 27.50 Hz
- Highest piano key (C8): 4186.01 Hz
Note by note
C3 · D3 · E3 · F3 · G3 · A3 · B3 · C4 · D4 · E4 · F4 · G4 · A4 · B4 · C5 · D5 · E5 · F5 · G5 · A5 · B5
Questions
What frequency is middle C?
261.63 Hz in standard tuning (A4 = 440 Hz).
Why is A4 440 Hz?
It was adopted as an international standard in the 20th century so instruments everywhere could play together. Some orchestras tune slightly higher, to 442 Hz.
How do I convert a frequency to a note?
Type it into the converter. It shows the nearest note and how many cents sharp or flat the frequency is.
More free tools
Online tuner · Online metronome · BPM tapper · Interval ear training · Chord ear training · Tone deaf test · Vocal range test · Binaural beats generator · Frequency sweep generator · White, pink & brown noise · Tone generator · Perfect pitch test · Hearing test