Note Frequency Calculator (Note to Hz and Back)

Every note on a piano or guitar has a frequency, and tuners, synthesizers and audio tools all work in hertz. This calculator converts a note such as C4 or F#3 to its exact frequency, or a frequency to the nearest note and how many cents sharp or flat it is. You can use the standard A4 = 440 Hz, alternatives such as 432, 442 or 443 Hz, Baroque pitch (415 Hz) or your own reference, and see the MIDI number, piano key, period and wavelength, with a table of nearby notes or all 88 keys.

How to use this tool

1. Choose note → frequency or frequency → note.
2. Type a note (A4, C#5, Bb3) or a frequency in hertz.
3. Pick the reference pitch for A4 and, if you need wavelengths, the speed of sound.
4. Read the result and use the table for neighboring notes or the whole piano.

Formula

f = A4 × 2^((n − 69) / 12) and n = 69 + 12 × log₂(f / A4)

n is the MIDI note number: A4 is 69 and middle C (C4) is 60, so each semitone adds 1. Cents measure the gap to the nearest note: 1200 × log₂(f / f_nearest), where 100 cents is one semitone. Piano key = n − 20, from A0 (key 1) to C8 (key 88). Wavelength = speed of sound ÷ frequency and period = 1 ÷ frequency. This is twelve-tone equal temperament, the tuning of modern pianos and most instruments.

Example

Middle C (C4) at A4 = 440 Hz is 440 × 2^(−9/12) = 261.6256 Hz, MIDI note 60 and key 40 on the piano, with a wavelength of 343 ÷ 261.63 = 1.311 m. With A4 at 432 Hz the same C is 256.87 Hz. A string sounding 445 Hz is A4, sharp by about 19.56 cents.