Convert a note name to its frequency
A4 is 440 Hz — but what about the C two octaves down, or the F# your synth is playing?
Tools used in this guide
The job
Pick a note and octave — the tool returns the frequency in Hz and the MIDI note number. Useful for tuning oscillators, identifying feedback frequencies, or converting sheet music to synthesis parameters.
A4 defaults to 440 Hz; change it for period performance (415 Hz), orchestra tuning (442 Hz), or experiments.
The math
Equal temperament divides the octave into 12 equal semitone ratios of 2^(1/12). Each step up multiplies frequency by that ratio — A4→A5 doubles 440 to 880 Hz.
Enharmonic equivalents are shown where they exist: C# and Db are the same key and frequency.
Where it does not apply
Real instruments drift from equal temperament — pianos stretch octaves, strings favor just intonation. The number is the theoretical center, not what a tuner will necessarily read.