Note to Frequency Converter
Convert any musical note and octave to frequency in Hertz, with optional alternate A4 reference tuning.
Choose a musical note
Each semitone changes frequency by a factor of 21/12. Changing the A4 reference updates every note frequency instantly.
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These are theoretical 12-tone equal-temperament frequencies. Real instruments may use alternate tuning systems or tuning adjustments.
A Note to Frequency Converter calculates the frequency of a musical note in Hertz. Choose a note, select its octave, set the A4 reference pitch, and the converter instantly shows the corresponding frequency.
This is useful for singers, musicians, producers, sound designers, music students, and anyone working with pitch. You can use the tool to answer questions such as “What frequency is C4?”, “What Hz is F#3?”, or “How does A4 = 432 Hz change note frequencies?”
If you need to work in the opposite direction, use the Hz to Note Converter to turn a frequency value into the nearest musical note.
How to Use the Note to Frequency Converter
The converter is designed to work instantly.
Choose the note you want to calculate, such as C, F♯, A, or B♭. Then select the octave number and confirm the reference tuning.
By default, the tool uses:
A4 = 440 Hz
The result updates automatically when you change any input.
For example, selecting:
- Note: C
- Octave: 4
- A4 reference: 440 Hz
produces a result of approximately:
C4 = 261.63 Hz
The result also shows useful related information such as the MIDI note number, semitone distance from A4, period in milliseconds, and frequencies one octave above and below.
If you want to verify a note using live audio rather than a theoretical calculation, use the Pitch Detector.
How Musical Notes Are Converted to Frequency
In 12-tone equal temperament, an octave is divided into 12 equal semitone steps.
Each semitone changes frequency by the same ratio:
2^(1/12)
To calculate the frequency of a note, the converter determines how many semitones the selected note is above or below A4 and applies that ratio to the chosen A4 reference frequency.
The relationship can be written as:
f = A4 × 2^(n / 12)
where:
- f is the calculated frequency;
- A4 is the selected reference frequency;
- n is the number of semitones from A4.
This mathematical relationship explains why moving one octave upward doubles the frequency.
For example:
- A3 = 220 Hz
- A4 = 440 Hz
- A5 = 880 Hz
when A4 is set to 440 Hz.
Understanding Note and Octave Names
A musical note such as C4 contains two pieces of information.
The letter identifies the pitch class, while the number identifies the octave.
This distinction is important because several notes can share the same letter but have very different frequencies.
For example:
- C3 ≈ 130.81 Hz
- C4 ≈ 261.63 Hz
- C5 ≈ 523.25 Hz
Each step of one octave approximately doubles the frequency.
The converter uses scientific pitch notation, where C4 is middle C.
If you are working with singers and want to understand how these notes relate to vocal ranges, the Vocal Range Calculator can help you interpret low and high notes in a singing context.
A4 = 440 Hz and Reference Tuning
Most modern tuning systems commonly use A4 = 440 Hz as a reference.
That means the A above middle C is assigned a frequency of exactly 440 Hz, and the frequencies of the other equal-tempered notes are calculated relative to it.
However, 440 Hz is not the only possible reference.
This converter also allows you to work with alternate tuning values such as:
- A4 = 415 Hz
- A4 = 432 Hz
- A4 = 440 Hz
- A4 = 442 Hz
Changing the reference frequency changes every calculated note frequency.
For example, C4 calculated with A4 = 432 Hz will be slightly lower than C4 calculated with A4 = 440 Hz.
That is why the converter always shows the active A4 reference alongside the result.
Sharp and Flat Notes
Some musical pitches have more than one commonly used name.
For example:
- C♯ and D♭
- D♯ and E♭
- F♯ and G♭
- G♯ and A♭
- A♯ and B♭
In standard 12-tone equal temperament, these enharmonic pairs are assigned the same frequency.
The converter lets you choose whether you prefer sharp or flat notation while keeping the underlying frequency unchanged.
The preferred spelling often depends on key, harmony, notation, or musical context.
Understanding the MIDI Note Number
The converter also shows the MIDI note number associated with the selected pitch.
MIDI assigns an integer number to each note, which is useful when working with:
- DAWs;
- synthesizers;
- MIDI controllers;
- virtual instruments;
- music programming;
- audio software.
For example, C4 corresponds to MIDI note 60 under the convention used by the converter.
This makes the tool useful beyond basic music theory, especially when matching musical notes to software or digital audio systems.
Frequency One Octave Above and Below
The result also shows the frequencies one octave above and one octave below the selected note.
The relationship is simple:
- one octave higher = frequency × 2;
- one octave lower = frequency ÷ 2.
So if a note has a frequency of 300 Hz:
- one octave below is 150 Hz;
- one octave above is 600 Hz.
This relationship is useful when studying vocal registers, synthesizer oscillators, harmonic structures, and instrument ranges.
You can also use the Octave Calculator when you need to compare pitch distances more directly.
What Does the Period Result Mean?
Frequency describes how many cycles occur every second.
The period describes how long one cycle lasts.
The converter displays period in milliseconds using the reciprocal relationship between frequency and time.
A lower-frequency note has a longer cycle period, while a higher-frequency note has a shorter one.
This value can be useful in technical audio work, synthesis, signal processing, and music production.
Practical Uses for Note-to-Frequency Conversion
A Note to Frequency Converter can be useful in many workflows.
Musicians can check theoretical note frequencies when tuning or studying intonation. Producers and sound designers can use the values when configuring oscillators, filters, modulation systems, or frequency-based effects.
Singers may also use note frequencies when comparing vocal pitches. If your goal is to measure your actual voice rather than calculate a theoretical note, try the Voice Frequency Test or Vocal Pitch Monitor.
For measuring intervals in semitone steps, the Semitone Calculator is another useful companion tool.
Accuracy and Limitations
The converter calculates theoretical equal-temperament frequencies.
The mathematical result is deterministic for the selected note, octave, and A4 reference, but real-world tuning may differ.
Acoustic instruments can deviate slightly because of:
- tuning systems;
- instrument construction;
- temperature;
- performance technique;
- stretched tuning;
- ensemble tuning practices.
The converter therefore tells you what the selected note corresponds to mathematically within the chosen equal-tempered reference system. It does not measure the actual frequency produced by a physical instrument or voice.
For live measurement, use a pitch-detection tool instead.
Frequently Asked Questions
What frequency is C4?
With A4 set to 440 Hz, C4 is approximately 261.63 Hz.
What frequency is A4?
A4 is 440 Hz when the reference tuning is set to A4 = 440 Hz. If you change the reference, the frequency changes accordingly.
Does frequency double every octave?
Yes. Moving exactly one octave higher doubles the frequency, while moving one octave lower halves it.
Are C# and Db the same frequency?
In 12-tone equal temperament, C♯ and D♭ are enharmonic equivalents and use the same frequency.
What is middle C in Hz?
Middle C is C4 and is approximately 261.63 Hz when using A4 = 440 Hz.
Why can I change A4 from 440 Hz?
Different musical contexts can use different reference pitches. Changing A4 allows the converter to calculate the entire tuning system relative to that reference.
Does this tool listen to my microphone?
No. The Note to Frequency Converter performs a mathematical conversion from the note and tuning values you select. For microphone-based analysis, use the Pitch Detector.
Can I use this for voice analysis?
You can use the results as theoretical pitch references. For direct vocal analysis, a tool such as the Singing Voice Test is more appropriate.