Note ↔ Frequency Converter

Note to Frequency Formula

In 12-tone equal temperament, the frequency of any note is calculated relative to a reference pitch (typically A4 = 440 Hz):

f = A4 × 2^{(n / 12)}

Where n is the number of semitones above or below A4.

Frequency to Note

To find the closest note for a given frequency:

n = 12 × log₂(f / A4)

The fractional part of n gives the deviation in cents (1 semitone = 100 cents).

Equal Temperament

Modern Western music uses 12-tone equal temperament (12-TET), where each octave is divided into 12 equal semitones. Each semitone corresponds to a frequency ratio of 2^1/12 ≈ 1.05946. This means every octave doubles in frequency (e.g., A4 = 440 Hz, A5 = 880 Hz).

Concert Pitch History

• 415 Hz — Baroque tuning (17th-18th century)
• 430-435 Hz — Classical era (late 18th century)
• 440 Hz — ISO 16 standard (1955), most widely used today
• 442-443 Hz — Used by some European orchestras for a brighter sound

MIDI Note Numbers

MIDI assigns number 69 to A4 (440 Hz). Middle C (C4) is MIDI note 60. The full MIDI range spans notes 0-127, covering C-1 to G9.

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