Musical Note Frequency Calculator

1. Choose the note name from the list.
2. Enter the octave in scientific pitch notation, where middle C is C4.
3. Leave the A4 reference at 440 Hz, or change it for a different tuning.
4. Read the frequency in hertz, plus the MIDI number, wavelength and period.

Note frequency is how fast a musical note vibrates, measured in hertz, or cycles per second. The A above middle C, the usual tuning reference, sits at 440 hertz. Every note has its own frequency, and doubling the frequency raises the pitch by exactly one octave.

Modern instruments use equal temperament, which divides the octave into twelve equal steps called semitones. This lets music play in any key, and it gives each note a precise, repeatable frequency. Knowing that exact number matters whenever you tune an instrument, program a synthesiser, or line up a sound effect with a musical pitch rather than an arbitrary one.

1. Find the note MIDI number from its name and octave.
2. Subtract 69, the MIDI number of A4, for the semitone distance.
3. Raise two to that distance divided by twelve.
4. Multiply by the A4 reference frequency.

Because each semitone multiplies the frequency by the twelfth root of two, twelve semitones exactly double it, which is why an octave up is twice the frequency.

Take middle C, written C4. Its MIDI number is 60, so it is 9 semitones below A4 at MIDI 69. The frequency is 440 times two to the power of minus 9 over 12, which is about 261.63 hertz. Go up an octave to C5 and the frequency doubles to about 523.25 hertz, while its wavelength in air halves.

The Note and Octave

Each step up the scale raises the frequency, and each octave doubles it, so position sets the pitch.

The Tuning Reference

Changing A4 from 440 to another value, such as 432 or 442, shifts every note by the same proportion.

Temperament

Equal temperament spaces semitones evenly; older just or meantone tunings give slightly different frequencies for the same note names.

Air and Wavelength

Frequency stays fixed, but the wavelength depends on the speed of sound, which changes a little with air temperature.

These are the equal-temperament frequencies with A4 at 440 hertz.

Notice how A5 at 880 hertz is exactly double A4, the clearest sign of the octave relationship.

Tuning by Ear or Tone

Get the exact hertz value to set a tuner, oscillator or reference tone.

Sound Design

Match a synth oscillator or filter to a musical pitch rather than a round number.

Learning Acoustics

See how notes, octaves and wavelengths relate when studying music or physics.

1. Mixing Octave Conventions

Some software calls middle C by C3 or C5; this tool uses scientific pitch, where middle C is C4.

2. Forgetting the Reference

Frequencies only match if the A4 reference is the same, so check whether you are at 440 or another pitch.

3. Assuming Sharps Differ from Flats

In equal temperament, C sharp and D flat are the same frequency.

4. Confusing Frequency and Wavelength

Higher notes have higher frequency but shorter wavelength; they move in opposite directions.

The equal-temperament maths is exact, so the frequencies are precise for the standard tuning system. Wavelength assumes a fixed speed of sound.

In equal temperament with A4 at 440 Hz, middle C (C4) is about 261.63 hertz. Its MIDI number is 60.

Multiply the A4 reference by two to the power of the semitone distance from A4 divided by twelve. A4 is 440 Hz, and each octave doubles the frequency.

Concert pitch is the agreed tuning reference, almost always A4 at 440 hertz, which fixes the frequency of every other note.

In equal temperament the octave is split into twelve equal semitones, so an enharmonic pair such as C sharp and D flat share one frequency.

It is the standard integer that software and keyboards use for each note. Middle C is 60 and A4 is 69, rising by one per semitone.

Each octave up doubles the frequency and each octave down halves it, so A3 is 220 Hz and A5 is 880 Hz.

Setting the A4 reference to 432 lowers every note proportionally. It is a niche alternative to the standard 440 hertz.

Divide the speed of sound, about 343 metres per second in air, by the frequency. A 440 Hz note is roughly 0.78 metres long.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Piano key frequencies (Wikipedia).
• Equal temperament (Wikipedia).
• MIDI tuning and note numbers (Wikipedia).