Get any note’s exact frequency, MIDI number and wavelength from its name and octave.
Equal temperament, A4 = 440 Hz by default. Change the reference pitch if your ensemble tunes differently.
frequency
How to use this tool
Choose the note name, including sharps, and its octave number (middle C is C4).
Standard tuning is A4 = 440 Hz; switch to 432 Hz or 415 Hz if your ensemble uses them.
The headline figure is the exact equal-tempered frequency, with the MIDI number used by keyboards and software.
The notes immediately below and above help when tuning by ear or checking a tuner reading.
Formula & worked example
A4 is 440 Hz (MIDI 69). C4, middle C, is 261.63 Hz, and C5 is exactly double at 523.25 Hz.
Limitations — read this before you rely on it
Equal temperament is a compromise: real instruments tune some intervals slightly away from these values, and the speed of sound varies with air temperature, so wavelengths are approximate.
Frequently asked questions
C4 at 261.63 Hz in the usual scientific pitch notation used here.
It is the ISO standard concert pitch, though some orchestras tune to 442 Hz and baroque ensembles often use 415 Hz.
A number for each piano key: middle C is 60, A4 is 69, and each semitone adds 1.
Use the tuner or a frequency-to-note tool: the nearest note comes from MIDI = 69 + 12 × log₂(f / 440).
Yes, because the speed of sound rises with temperature, but the frequency of a tuned note itself does not change.