HesapHanem

Note to Frequency Calculator

Enter a note name to find its frequency in hertz.

How it is calculated

The note name is turned into a MIDI number, then into a distance in semitones from A4: midi = (octave + 1) × 12 + semitone, n = midi − 69 and f = A4 × 2^(n ÷ 12). Semitone offsets are C 0, D 2, E 4, F 5, G 7, A 9, B 11, plus 1 for a sharp (#) and minus 1 for a flat (b). Type the note as letter, optional accidental and octave number, such as C4, F#5 or Bb3. Case and spaces do not matter, and negative octaves work. A4 is the reference pitch in Hz; if it is empty or not above zero, 440 is used. The frequency is shown with three decimals. Anything the tool cannot read as a note, such as H4, returns no result. It uses equal temperament, where C4 is middle C.

Worked example

Note Eb4 with A4 at 440 Hz. E is 4 and the flat takes 1 off, giving 3. MIDI number: (4 + 1) × 12 + 3 = 63. Distance from A4: 63 − 69 = −6 semitones. Frequency: 440 × 2^(−6 ÷ 12) = 311.127 Hz, which is half an octave below A4.

Try this example →

Common mistakes

  • Leaving out the octave number. A bare E or Eb is not accepted; write E4 or Eb4, because the same letter in another octave has a different frequency.
  • Using the German name H for B. The tool reads only the letters A to G, so H4 gives no result; use B4.
  • Mixing up octave labelling between instruments. Here middle C is C4, but some keyboards and software label it C3 or C5, which is a factor of two in frequency.
  • Typing a double flat or a flat symbol. Use a single # or b after the letter.
  • Changing the A4 reference for the wrong reason. A value like 432 or 442 moves every note by the same ratio, so leave it at 440 unless your ensemble tunes differently.

About this calculator

In equal temperament — the tuning system used by virtually all modern Western instruments — each semitone is a fixed frequency ratio of the 12th root of 2 (≈1.05946) apart. This calculator finds a note's frequency with f = A4 × 2^((midi − 69)/12), where midi is the note's MIDI number (A4 = 69; the range is not limited to the 88 piano keys) and A4 is the reference pitch, adjustable from the concert standard of 440 Hz to alternate tunings like 442 Hz used by some European orchestras.

Musicians tuning instruments by ear or electronic tuner, audio engineers designing synthesizers, and piano technicians rely on this note-to-hertz relationship daily — it's the same math behind every digital tuner and synth oscillator. Because equal temperament slightly compromises the “pure” harmonic ratios found in just intonation, the calculator is also a useful reference for anyone studying the difference between the two tuning systems.

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Comments (1)

  • Editorial team

    Besides the frequency, the tool shows the MIDI number and the semitone distance from A4, which makes it handy for cross-checking a synth, tuner or DAW. A quick sanity test is that the same letter one octave up must show exactly double the hertz: E2, the low string of a guitar, comes out at 82.407 Hz at A4 440, and E3 is 164.814 Hz. Do you tune to 440, 442 or something else, and for which instrument?

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