How it works
The Frequency to Note converter identifies the closest musical pitch (note name, octave, and MIDI number) for any audio frequency in Hz, and shows how many cents sharp or flat the frequency is from the exact equal-temperament pitch — useful for instrument tuning, synthesizer calibration, fork tuning, and understanding the relationship between physics and music theory.
Equal temperament: modern Western music divides each octave into 12 equal semitones. Each semitone is a frequency ratio of 2^(1/12) ≈ 1.05946. A4 is defined as 440 Hz (the international standard tuning reference, ISO 16). Every other note's frequency is A4 × 2^((midi − 69) / 12), where MIDI number 69 is A4.
Cents: a cent is 1/100 of a semitone, or 1/1200 of an octave. The human ear can typically detect a deviation of 5–10 cents. A frequency that is 50 cents from the nearest note is equally distant from two adjacent notes. Professional instrument tuning targets within ±2 cents.
MIDI numbers: the MIDI standard assigns integer numbers to notes: C4 (middle C) = 60, A4 = 69. The range for standard 88-key piano is A0 (MIDI 21, 27.5 Hz) to C8 (MIDI 108, 4186 Hz). MIDI numbers are used in DAWs, synthesizers, and digital instruments.
Common reference frequencies: A4 = 440 Hz, A3 = 220 Hz, A5 = 880 Hz, C4 (middle C) = 261.63 Hz, E4 = 329.63 Hz, G4 = 392 Hz. The quick-access buttons for these common reference values allow fast navigation without typing.
Alternative tuning systems: some musicians tune to A = 432 Hz (claimed to be "more natural"), A = 415 Hz (Baroque tuning), or A = 443 Hz (common in European orchestras). Enter any frequency to find its note identity regardless of tuning standard.
Privacy: all frequency calculations are pure math, performed locally.
Frequently Asked Questions
- A cent is 1/100 of a semitone (1/1200 of an octave). The cents deviation shows how far the input frequency is from the nearest equal-temperament pitch. +20¢ means the frequency is 20 cents sharp (higher) than the exact note. -15¢ means 15 cents flat (lower). The human ear typically detects deviations of 5–10 cents. Professional instrument tuning targets within ±2 cents. A deviation of ±50¢ places the frequency exactly halfway between two adjacent notes.
- A4 = 440 Hz was adopted as the international standard tuning reference by ISO 16 in 1975. Before standardization, A4 ranged from 415 Hz (Baroque period) to over 450 Hz (19th century orchestras). The 440 Hz standard was necessary for international ensemble playing, broadcast tuning, and keyboard instrument manufacturing. Some musicians prefer A4 = 432 Hz (claimed to be 'more natural') or A4 = 443 Hz (common in some European orchestras) — enter these frequencies to see they map to A4 with a cents deviation.
- The calculation is mathematically exact — it uses the equal temperament formula directly, with floating-point precision. The MIDI number is rounded to the nearest integer, and the cents deviation reflects the difference between the exact MIDI value and its rounded integer. For any frequency you type, the result is the same as what a professional tuner app would display.
- The tool accepts any positive frequency. Musically, the standard piano range is A0 (27.5 Hz) to C8 (4186 Hz). Below A0, the notes are subcontra octave (musical but below standard instruments). Above C8, the notes are in the 8th octave and above — valid mathematically but above the range of standard instruments. The human hearing range is approximately 20 Hz to 20,000 Hz.