Tool
Note frequency calculator
Choose a note and an octave to read hertz, or enter a frequency to find the nearest note and the offset in cents. The default reference is A4 = 440 Hz. MIDI 69 is A4.
Note to hertz
Hertz to nearest note
Common practice values include 432, 440, and 442. The allowed range on this page is 400–480 Hz.
When to use note frequency
Use this page when you need the equal-tempered frequency of a written pitch, or when you have a frequency and want the nearest note name. The formula is f = A4 × 2((midi − 69) / 12).
A4 is 440 Hz unless you change the reference. MIDI note 69 is A4 at that reference. Names use C, D, E, F, G, A, and B. In some countries the note B is written H; this page uses B. Upward chromatic names prefer sharps.
This is a practice calculator, not a hardware tuner. A concert room still needs an instrument, a tuner, and ears.
Read the A440 and MIDI 69 guide for the same formula in prose.
Worked examples
The frequency is 440.00 Hz, MIDI 69. If you type 440 in the reverse field, is A4 the nearest note with 0.0 cents?
With the reference set to 442, A4 is 442 Hz. Does your ensemble actually sit at 442, or are you still at 440?
The nearest note is still A4, about +19.6 cents. Is that a sharp A, or did you mean a different reference?
Questions
What happens if frequency is 0 or empty?
The field shows an error. Hertz must be greater than 0. The page will not print Infinity.
Can I use 432 Hz?
Yes. Set the reference to 432. Then A4 is 432 Hz and the rest of the octave moves with the same formula.
Is this a tuner I can trust on stage?
No. Use it to learn the numbers. A dedicated tuner and the room you are in still decide concert pitch.