Frequency to note converter
Type a frequency such as 440 or 261.6 to see the nearest note, how far off it is in cents and its MIDI number. Type a note such as C4 or F#3 to get its frequency. The reference pitch for A4 is adjustable, so the tool also works for baroque pitch or 432 Hz tuning.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type a frequency in hertz, or a note name with its octave, in the first box.
- Change the A4 reference pitch if you do not use 440 Hz.
- For a frequency you see the nearest note, the offset in cents (plus means sharp, minus flat), the exact frequency of that note and its MIDI number. For a note you see its frequency.
- Note number from frequency: n = 69 + 12 × log2(f ÷ A4).
- Frequency from note number: f = A4 × 2^((n − 69) ÷ 12).
- Cents: 100 × (n exact − n rounded).
Worked example
450 Hz with A4 = 440 Hz gives 12 × log2(450 ÷ 440) = 0.389 semitones above A4. The nearest note is A4 and the difference is +38.9 cents, almost halfway to B♭. With A4 = 432 Hz, the note A4 is exactly 432 Hz.
Tips
- To tune by ear, play a reference note with the tone generator and compare.
- Frequencies below 20 Hz are felt rather than heard, and most instruments do not go above about 4,200 Hz (C8).
Frequently asked questions
How is the nearest note calculated?
In equal temperament each semitone is a factor of the twelfth root of 2. The note number is 69 + 12 × log2(f ÷ 440), rounded to the nearest whole number, where 69 is A4. The distance from the exact value, times 100, is the difference in cents.
What is a cent?
A cent is one hundredth of a semitone. Most people cannot hear differences below about 5 cents, and a tuner usually calls a note in tune within a few cents.
Why can the A4 reference pitch be changed?
Most music today is tuned to A4 = 440 Hz, but orchestras often tune a little higher, baroque ensembles tune lower, and some people prefer A4 = 432 Hz. The tool recalculates every note from the reference pitch you enter, between 300 and 600 Hz.
What note is middle C?
Middle C is C4, MIDI note 60, at about 261.63 Hz with A4 at 440 Hz. This tool numbers octaves so that C4 is middle C, and MIDI 0 is C-1.
What is the wavelength shown for?
It is the distance one cycle of the sound travels in air, assuming the speed of sound is 343 metres per second (air at 20 °C). It is useful for room acoustics and for understanding why low notes need a lot of space.