Frequency to MIDI Note
Convert any frequency to its nearest MIDI note and pitch deviation in cents.
Overview
The frequency-to-MIDI tool takes any frequency in Hertz and returns the nearest MIDI note number, the note name, and the deviation in cents from the exact pitch. Drop in 440 Hz and you get MIDI 69, A4, 0 cents. Drop in 445 Hz and you get the same MIDI 69 but +19.6 cents sharp.
It's a working tool for synth designers tuning oscillators, audio analysts checking the pitch of a recorded sample, instrument builders setting up just-intonation scales against equal temperament, and educators showing students how MIDI's integer note numbers relate to real-world frequencies. It also flips the other way: enter a MIDI note and get its frequency.
How it works
The MIDI standard assigns integer note numbers from 0 to 127, with A4 (concert pitch) defined as MIDI 69. Each MIDI step is one equal-tempered semitone — 100 cents, or a frequency ratio of 2^(1/12). The formula is f = 440 x 2^((n - 69) / 12), so MIDI 60 (middle C) lands at about 261.63 Hz and MIDI 81 (A5) at 880 Hz.
To go the other way, the tool computes n = 69 + 12 x log2(f / 440) and rounds to the nearest integer. The fractional remainder, multiplied by 100, gives the cent deviation. Concert pitch is configurable: orchestras sometimes tune to A4 = 442 Hz, baroque ensembles to A4 = 415 Hz, and synthesists occasionally to other reference points, which shifts every MIDI-to-frequency mapping accordingly.
Examples
440 Hz → MIDI 69 (A4), +0 cents
261.63 Hz → MIDI 60 (C4), +0 cents (middle C)
445 Hz → MIDI 69 (A4), +19.6 cents
523.25 Hz → MIDI 72 (C5), +0 cents
FAQ
What does MIDI 0 sound like?
MIDI 0 is C-1, about 8.18 Hz — well below human hearing. It exists as a numerical placeholder; in practice usable musical pitches start around MIDI 21 (A0 = 27.5 Hz, the lowest piano note).
Why doesn't my synth match the standard frequencies exactly?
Analog oscillators drift; digital synths can be perfectly accurate but may use a different reference (A4 = 442 instead of 440). Check your global tuning setting if you suspect a mismatch.
Can MIDI represent microtones?
Standard MIDI uses integer note numbers, so no. MIDI 2.0 and pitch-bend or tuning-table extensions can represent microtonal pitches.
Why is A=440 the modern standard?
It was ratified by ISO in 1955 as a compromise between historical tunings that ranged from roughly 415 to 466 Hz. Some orchestras still tune sharper (442-444) for brightness.
How accurate is the cent-deviation reading?
It's an exact mathematical conversion. The audible accuracy of the source depends on how stable the input frequency is — vibrato, formants, and noise spread the energy across nearby frequencies.