Hz to Musical Note Converter

Every audible frequency corresponds to a musical pitch — exactly on a note or some number of cents away from it. This converter takes a frequency in Hz and tells you the nearest equal-temperament note, its octave, its MIDI number, and precisely how sharp or flat the input is.

How it works

Equal temperament divides each octave into twelve equal semitones. The position of any frequency on the MIDI scale is:

n = 69 + 12 · log2(f / A4)

where A4 is the reference pitch (440 Hz by default, mapped to MIDI 69). Rounding n to the nearest integer gives the closest note. The leftover fraction, multiplied by 100, is the deviation in cents:

cents = (n − round(n)) · 100

The exact frequency of that nearest note is recovered with A4 · 2^((round(n) − 69) / 12), which the tool also displays so you can see your target.

Reference: equal-temperament frequencies for the central octave

For A4 = 440 Hz, the twelve notes of octave 4 (middle octave) are:

Each octave above doubles every frequency; each octave below halves it. Middle C at 261.63 Hz is therefore an octave below C5 at 523.25 Hz.

The custom A4 reference and why it matters

Standard concert pitch is A4 = 440 Hz, established internationally in 1939. However, several situations call for a different reference:

• Baroque ensembles commonly tune to A4 = 415 Hz (approximately one semitone flat of modern pitch), to match historical instrument tuning.
• Some orchestras tune slightly higher, to 442 or 444 Hz, for a brighter sound.
• Alternative tuning communities use 432 Hz, which they believe has different acoustic qualities (a position not supported by acoustic physics, but the preference is personal and valid for creative purposes).
• Electronic music may need to match a specific synth or sample pack tuned to a non-standard reference.

When the A4 reference changes, every note’s frequency shifts proportionally. The converter recalculates all note positions so that, for example, entering 415 Hz with a 415 Hz reference returns exactly A4 at 0 cents.

Practical uses

• Tuning an instrument: Read the frequency from a spectrum analyser or tuner, enter it here, and see how many cents off you are and in which direction.
• Transcribing a recording in non-standard tuning: Enter a few reference notes to determine the A4 reference of the recording before transcribing.
• Electronic music and synthesis: Confirm that a synth’s output at a given MIDI note matches the expected frequency for your project’s tuning system.
• Acoustics and physics: Convert machine vibration frequencies, room resonances, or signal frequencies into musical context.

Tips

• Use the cents value to decide which way to tune: positive means the pitch is sharp — lower it. Negative means flat — raise it.
• Within ±5 cents is generally perceived as in tune by most listeners in a musical context.
• Match the A4 reference to your ensemble before trusting the note name, especially for frequencies near octave boundaries.

The conversion runs entirely in your browser.