Note Frequency Calculator
Convert any note and octave into its frequency, MIDI number and wavelength.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Every note frequency follows from A4 at 440 hertz by multiplying by the twelfth root of two for each semitone, which is what makes equal temperament work. Doubling the frequency raises a note by exactly one octave.
Worked example
calculated with the default values below
Note A · Octave 4 · Concert pitch 440 Hz Frequency 440.00 Hz · MIDI note number 69 · Wavelength in air 78.0 cm · Cents from A4 0 · Semitones from A4 0 · Enharmonic name A has no common enharmonic name · One octave above 880.00 Hz
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
f = A × 2^(((O+1)×12 + s − 69)/12)
- f
- frequency, Hz
- A
- reference frequency A4, Hz
- O
- octave number
- s
- semitone index, C = 0
MIDI number = (O+1)×12+s; wavelength = 343/f×100 cm (speed of sound 343 m/s); cents from A4 = (MIDI−69)×100; octave above = 2f.
Frequently asked questions
Why can I change A4 to 432 Hz and get different note frequencies?
The calculator builds every frequency from the concert pitch you enter, so the default A4 is 440 Hz and each semitone is the twelfth root of two times the last. Lowering concert pitch to 432 Hz shifts A4 down and pulls every other note with it, since all frequencies are relative to that reference. The range 380–500 Hz covers historical and alternative tunings.