Note-frequency calculator

Note names and octave numbers

This tool uses twelve-tone equal temperament and scientific pitch notation: middle C is C4 (MIDI 60), and A4 is MIDI 69. With A4 set to 440 Hz, C4 is about 261.625565 Hz. Adjacent semitones have a frequency ratio of 2^1/12; an octave doubles the frequency.

What does the cents meter show?

One semitone is 100 cents. A positive offset is sharp of the nearest note; a negative offset is flat. With concert A at 440 Hz, a 445 Hz tone is nearest A4 and about 19.56 cents sharp. Changing the A4 reference changes every calculated note frequency.

Calculation and reference audio

For MIDI note number m, frequency = A4 × 2^{(m − 69)/12}. To convert a frequency f, compute m* = 69 + 12 log₂(f/A4), then round to the nearest note m. The offset is 100(m* − m) cents. The UNSW note-frequency reference explains these relationships.

Note input covers C−1 through G9 (MIDI 0–127); Hz input covers 20–10,000. A nearest note outside MIDI 0–127 is labeled accordingly. A4 can be set from 400 to 480 Hz. Sharp and flat names such as C♯/D♭ describe the same frequency in this model. Other tuning systems can give different results.

“Play input tone” plays the calculated or supplied frequency for two seconds; “Play nearest note” plays its equal-tempered target. Start with a low device volume. Playback is limited to 20–10,000 Hz, stops when inputs change or the tab is hidden, and depends on your browser and audio device. The drawn sine wave illustrates frequency mathematically; it is not a microphone measurement. This tool does not listen to or certify an instrument's tuning.

Use the tap-tempo and delay calculator for beat rates, or practice layered pulses with the polyrhythm metronome.