Note Frequency Converter
In equal temperament every semitone is the same ratio, the twelfth root of two. With A4 set to 440 hertz, any note frequency is 440 multiplied by two to the power of the number of semitones from A4, divided by twelve. Middle C, written C4, comes out at 261.63 hertz.
| Note | Frequency | MIDI |
|---|---|---|
| A0 | 27.50 Hz | 21 |
| A1 | 55.00 Hz | 33 |
| A2 | 110.00 Hz | 45 |
| A3 | 220.00 Hz | 57 |
| A4 | 440.00 Hz | 69 |
| A5 | 880.00 Hz | 81 |
| A6 | 1760.00 Hz | 93 |
| A7 | 3520.00 Hz | 105 |
How to convert a musical note to its frequency
Choose a direction
Pick note to frequency, or frequency to note if you have a reading from a tuner or an analyser.
Enter the value
Type a note with its octave, such as A4, C#3 or Bb2, or type a frequency in hertz.
Set the reference pitch
A4 defaults to 440 Hz. Switch to 415 for baroque pitch, or 442 and 444 if your ensemble tunes sharp.
Read the result
You get the note, the frequency, and either the MIDI note number or how many cents off the nearest note you are.
Why use this tool
Both directions
Note to hertz for writing synth patches, and hertz to note for reading a tuner or a spectrum analyser.
Adjustable reference pitch
A4 can be set to 415, 430, 432, 440, 442 or 444 Hz, because 440 is a modern convention rather than a fixed law of music.
Cents off the nearest note
Enter any frequency and see how far it sits from the nearest named note, which is exactly what a tuner display shows.
MIDI note numbers
Every result carries its MIDI number, so a note name can go straight into a sequencer or a synth.
Flats and sharps both accepted
Bb2 and A#2 are the same note and both parse, so you can type whichever the score uses.
About this tool
Western music divides the octave into twelve equal steps, an arrangement called equal temperament. Equal here means equal in ratio rather than in hertz: each semitone multiplies the frequency by the twelfth root of two, roughly 1.0595. Twelve of those multiplications double the frequency, which is why an octave up is exactly twice the pitch and why the gaps between notes get wider as you go higher.
Everything is anchored to one agreed note. By convention that is A above middle C, written A4, fixed at 440 hertz. From there any note is 440 multiplied by two raised to the power of its distance in semitones from A4, divided by twelve. Middle C, four octaves and nine semitones below the top of that reference, lands on 261.63 hertz. MIDI numbers follow the same ladder with A4 as note 69, which is why they map cleanly onto frequencies.
The 440 standard is more recent and less universal than it looks. Baroque ensembles commonly tune to 415 hertz, roughly a semitone flat, and some European orchestras sit at 442 or 444 to sound brighter. That is why the reference is adjustable here rather than fixed. When you go from a frequency back to a note, the result also reports cents, where 100 cents is one semitone: that is the number a tuner shows you, and anything within about 5 cents will read as in tune. For related work there is the frequency converter for plain unit changes, the time unit converter for tempo arithmetic, and the scientific notation converter for very large or small values.
Frequently asked questions
- What frequency is middle C?
- Middle C, written C4, is 261.63 hertz when A4 is tuned to 440 hertz. Its MIDI note number is 60.
- How do I calculate a note frequency by hand?
- Count the semitones from A4, positive going up and negative going down, then compute 440 times 2 to the power of that count divided by 12. C5 is three semitones above A4, giving 440 times 2 to the power of 0.25, or 523.25 hertz.
- Why can the A4 reference be changed?
- Because 440 hertz is a twentieth-century convention, not a property of music. Baroque performance commonly uses 415 hertz, which is close to a semitone lower, and some orchestras tune to 442 or 444.
- What is a cent?
- One hundredth of a semitone, so 1,200 cents make an octave. Tuners display cents because the ear notices ratio differences rather than hertz differences, and about 5 cents is the point where most listeners start to hear a note as out of tune.
- Are Bb and A# the same note?
- In equal temperament, yes, they are the same pitch and this tool accepts either spelling. In other tuning systems and in some notation contexts they are treated as distinct, but their frequency here is identical.
- Is my data uploaded anywhere?
- No. The calculation runs in your browser and nothing you type leaves your device.
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