Frequency to Note Calculator
Converts any audio frequency in Hz to its closest musical note and MIDI number, with support for custom tuning standards. Useful for tuning instruments, analyzing recordings, and exploring alternative temperaments.
About this calculator
In standard equal temperament, the MIDI note number for a given frequency is derived using logarithms: MIDI = round(12 × log₂(frequency / tuningStandard) + 69 + (octaveNumber − 4) × 12). The number 69 corresponds to A4 in MIDI notation. The log₂ term counts how many semitones the input frequency is above (or below) the reference. Dividing by the tuning standard (typically 440 Hz for A4) normalizes the frequency before the log. The octave offset term (octaveNumber − 4) × 12 shifts the reference octave when you want to anchor to a different register. The result is rounded to the nearest integer to snap to a named note, and the fractional remainder gives the deviation in cents.
How to use
Say you record a tone at 523.25 Hz and want to identify it, using a 440 Hz tuning standard and reference octave 4. Calculation: MIDI = round(12 × log₂(523.25 / 440) + 69 + (4 − 4) × 12) = round(12 × log₂(1.1892) + 69) = round(12 × 0.2496 + 69) = round(2.995 + 69) = round(71.995) = 72. MIDI note 72 is C5, which is exactly middle C one octave up. The tiny deviation from 72.000 shows this frequency is almost perfectly in tune.
Frequently asked questions
How do I convert a frequency in Hz to a musical note name using this calculator?
Enter the frequency in hertz, set the tuning standard (440 Hz is the default concert pitch), and choose your reference octave. The calculator applies the formula MIDI = round(12 × log₂(f / tuningStandard) + 69 + (octaveNumber − 4) × 12) and maps the result to a note name using the standard MIDI note table. MIDI 69 is A4, 70 is A♯4, 71 is B4, 72 is C5, and so on. Any fractional remainder is the pitch deviation in cents, useful for checking tuning accuracy.
What tuning standard should I use when identifying notes in old or non-standard recordings?
Concert pitch has varied significantly throughout history. Baroque ensembles often used A = 415 Hz, roughly a semitone below modern standard. Some orchestras use A = 442 or 443 Hz for a brighter sound. For analyzing a recording, you can measure the frequency of a known note and back-calculate the tuning standard used. Entering the correct tuning standard ensures the calculator maps every note correctly rather than showing systematic sharp or flat offsets throughout the piece.
Why does changing the reference octave number affect the note calculator result?
The reference octave parameter shifts the anchor point of the MIDI numbering system. By default, MIDI 69 = A4 at 440 Hz. If you change the reference octave to 3, the formula adds (3 − 4) × 12 = −12 semitones, shifting all note assignments down by one octave. This is useful when working with instruments or software that use a different octave numbering convention, such as some synthesizers that label middle C as C3 rather than C4.