Note Frequency Calculator

Convert between a musical note and its frequency in 12-tone equal temperament (A4 = 440 Hz by default, adjustable). Pick a note and octave to get its frequency, MIDI note number, and wavelength in air, or enter a frequency to find the nearest note and how many cents it is off. Everything runs locally in your browser.

Note Octave

Reference pitch & speed of sound

A4 = Hz Speed of sound m/s

Enter a note or frequency to convert.

12-tone equal temperament: f = ref × 2^{(midi − 69) / 12}, where MIDI note 69 is A4 and the reference is A4's frequency (default 440 Hz). MIDI note 0 is C-1; each octave spans 12 semitones and doubles the frequency. Wavelength uses λ = v / f with the speed of sound in air (default 343.27 m/s at ~20 °C). In the reverse direction, the nearest note is found and the offset is shown in cents (1200 cents per octave, 100 per semitone). Everything runs locally — nothing leaves your browser.