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MIDI Note to Frequency Converter - Online Music Tuning

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A4 Reference: Hz A4 = 440.0 Hz
MIDI
0 (C-1) 127 (G9)
A4
440.00 Hz
Octave 4
Hz
A4
MIDI Note: 69
±0.0 cents
Exact match
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C2 – C6 (MIDI 36–84)
Octave Reference (C Notes) based on A4 = 440 Hz
OctaveNoteMIDIFrequency (Hz)
Frequently Asked Questions

The standard formula is: f = 440 × 2(n−69)/12, where n is the MIDI note number (0–127) and f is the frequency in Hz. MIDI note 69 corresponds to A4 at 440 Hz. Each semitone step multiplies or divides the frequency by the 12th root of 2 (≈1.059463).

Middle C is MIDI note 60, labeled as C4 in scientific pitch notation. At standard A4=440Hz tuning, C4 has a frequency of approximately 261.63 Hz. The octave number is calculated as floor(n/12) − 1.

A cent is a logarithmic unit of measure for musical intervals. One semitone equals 100 cents, and one octave equals 1200 cents. The formula is: cents = 1200 × log₂(f₁/f₂). Deviations within ±5 cents are generally considered in tune; ±10–20 cents is noticeably off for most listeners.

A4=440 Hz became the ISO 16 international standard for concert pitch in 1955. Historically, tuning varied widely (from ~415 Hz in Baroque to ~460 Hz in some 19th-century orchestras). Some modern orchestras tune to 441 Hz or 442 Hz for a brighter sound. This tool lets you adjust the reference frequency to match your needs.

MIDI supports 128 notes (0–127), spanning from C−1 (≈8.18 Hz) to G9 (≈12,544 Hz). This covers about 10.5 octaves — well beyond the range of a standard 88-key piano (MIDI 21–108, A0 to C8). The human hearing range is roughly 20 Hz to 20,000 Hz.

Use the inverse formula: n = 69 + 12 × log₂(f / 440). Round to the nearest integer to get the MIDI note number. Our tool also calculates the cents deviation between your input frequency and the exact standard frequency of that note — useful for fine-tuning instruments or detecting pitch drift.

Equal temperament (used by MIDI) divides each octave into 12 equal semitones. The frequency ratio between adjacent notes is always 21/12. Just intonation uses simple integer ratios (like 3:2 for a perfect fifth), which sound more "pure" but are key-dependent. This converter uses the equal-tempered MIDI standard.
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