How to use the note frequency converter
- Choose Note to frequency to find the pitch of a note, or Frequency to note to find the nearest note to a sound.
- Type a note such as A4, C#5 or Eb3, or type a frequency in hertz.
- Open More options to change the A4 reference, which starts at 440 Hz as an example.
- Read the headline, then the neighboring notes in the table. Copy, Print or export the CSV.
Formula
frequency = A4 x 2^((MIDI number - 69) / 12)
MIDI number = 69 + 12 x log2(frequency / A4)
cents off = (exact MIDI number - nearest whole number) x 100
In equal temperament each semitone is the twelfth root of 2 higher than the one below. Middle C is C4 and MIDI number 60, and A4 is MIDI number 69. A cent is a hundredth of a semitone.
C4 and a 450 Hz sound
Middle C is MIDI number 60, nine semitones below A4. With A4 at 440 Hz, 440 x 2^(-9/12) = 261.62557 Hz. A5 is 880 Hz and A0 is 27.5 Hz.
For 450 Hz, 69 + 12 x log2(450 / 440) = 69.389, so the nearest note is A4 and the sound is 38.9 cents sharp. A pitch within 0.05 cents of a note is shown as in tune.
Equal temperament and reference pitch
Most modern instruments and keyboards are tuned to equal temperament, which divides the octave into twelve equal steps. That makes the frequency of any note a simple power of two away from A4. Other tuning systems exist and give slightly different values, and strings, voices and winds can bend pitch.
A4 = 440 Hz is a common reference in modern tuning, and it is an agreed convention and not a law of nature. Some orchestras tune a little higher and some early-music groups lower, so the reference is editable here.
Octave numbering
Notes are named with a letter and an octave number, where the octave starts at C. Middle C is C4 in scientific pitch notation, but some software calls it C3 or C5, so check the convention when you move between programs. Flats are written with b and sharps with #, and enharmonic pairs such as C# and Db give the same pitch.
To hear notes, try the online piano or the online tuner. To change a song to another key, the chord transposer and the circle of fifths help.
Assumptions and limits
- Notes run from C-1 to G9 (MIDI numbers 0 to 127). Frequencies must be 8 to 14,000 Hz and must fall within that range of notes.
- The A4 reference can be set from 200 to 1,000 Hz. The 440 Hz default is an example.
- Equal temperament is assumed. Just intonation and other systems differ by a few cents.
- Nothing is stored or uploaded, and the page makes no sound.
Frequently asked questions
What frequency is middle C?
Middle C (C4) is about 261.63 Hz when A4 is 440 Hz. The converter gives 261.62557 Hz before rounding.
How do I find the note for a frequency?
Take 12 times the base 2 logarithm of the frequency divided by 440, add 69, and round. That is the MIDI note number. The converter above does this and also tells you how many cents the sound is from the nearest note.
What is a cent in music?
A cent is one hundredth of a semitone. Most listeners start to notice a note is out of tune when it is a few tens of cents away, depending on the sound and the context.
Why does my software call middle C a different name?
Octave numbering is a convention. Scientific pitch notation calls middle C C4, but some programs label it C3 or C5. Check the setting if the octave looks wrong.