Note ↔ Frequency

Enter a note name, a frequency in Hz or a MIDI number and get the other two, with cents offset, wavelength and piano key number. A second tab converts between concert and written pitch for transposing instruments.

How to use

1. On the "Convert" tab, choose the "Input" type and enter the value. Write note names with their octave, such as A4, C#5 or Bb3.
2. For a frequency, the nearest note and its cents offset appear; for a note or MIDI number, the frequency, period, wavelength and piano key number appear.
3. Under "Reference A4", pick 442 Hz or another value, and choose sharps or flats under "Spelling". Open "All notes (C0 to B8)" to see and copy the full table.
4. On the "Transpose" tab, choose the "Direction" and "Instrument", enter notes separated by commas, and pick a "Key" to see the transposed key signature.

How it works

• 12-tone equal temperament: frequency = A4 × 2^((MIDI − 69) ÷ 12). A4 is MIDI 69; middle C (C4) is MIDI 60 and 261.63 Hz with A4 = 440 Hz. One cent is 1/100 of a semitone.
• Wavelength uses the speed of sound in air at 20 °C, 343 m/s. Piano key numbers follow an 88-key piano (A0 = 1, C8 = 88).
• A B♭ instrument sounds a major second lower than written, an E♭ alto saxophone a major sixth lower and an F horn a perfect fifth lower. Inputs and settings stay in this browser.

Questions and answers

What frequency is A4?

The international standard is 440 Hz, MIDI 69. Some orchestras tune to 442 or 443 Hz; changing "Reference A4" moves every note.

What is the frequency of middle C?

With A4 = 440 Hz, middle C (C4) is 261.63 Hz, MIDI 60 and piano key 40. With A4 = 442 Hz it is 262.81 Hz.

Which note does a B♭ clarinet play to sound a concert C?

A written D, one whole step higher. Music in concert C major is written in D major for a B♭ instrument.

What is a cent?

One hundredth of a semitone. For example, 445 Hz is about 20 cents above A4 at 440 Hz.