Frequency to Note Converter: Hz to Musical Notes

What Is Frequency-to-Note Conversion?

Every musical pitch is a frequency. Middle C vibrates at 261.63 Hz; the A above it at 440 Hz. But frequencies are continuous — 437.2 Hz is a real sound — while note names are discrete slots. The converter finds the nearest slot and tells you how far off you are in cents, so a tuner, a DAW, and a musician can all agree on what they are hearing.

Key Takeaways

• 440 Hz = A4 under the international ISO 16 concert-pitch standard — but A4 is not always 440 Hz (see below).
• Formula: MIDI note number n = 69 + 12 × log₂(f ÷ 440); the note name comes from n.
• The converter also reports cents deviation — how sharp or flat the frequency is versus the nearest note.
• Middle C is C4 (261.63 Hz) in scientific pitch notation, but some keyboards label it C3.
• A mystery 60 Hz buzz in the US (50 Hz in Europe) is almost always mains hum, not a musical note.

How This Converter Works

This converter maps any frequency to the 12-tone equal-tempered chromatic scale using the MIDI note-number formula: n = 69 + 12 × log₂(f ÷ 440), where 69 is the MIDI number of A4. The note name comes from the rounded value of n (C, C♯, D … B repeating every 12), the octave from its register, and the cents deviation from the fractional remainder — positive for sharp, negative for flat.

Methodology: the A4 reference defaults to 440 Hz per ISO 16 but is adjustable from 430–450 Hz, because real ensembles do not all tune to 440 (see the A4 section below). Results assume 12-tone equal temperament. We verified this converter against a published 88-key piano frequency table for all notes A0–C8 — every conversion matched to two decimal places. Last reviewed: October 2026.

The Conversion Formula and Worked Examples

The single formula behind this tool:

Worked example 1 — 440 Hz: n = 69 + 12 × log₂(440 ÷ 440) = 69 + 0 = 69 → A4, 0 cents deviation. Perfectly in tune.

Worked example 2 — 432 Hz: n = 69 + 12 × log₂(432 ÷ 440) = 69 − 0.3177 = 68.68. The nearest whole number is 69, so the note is A4 at −31.77 cents (flat). This matches the cents calculator result exactly.

Worked example 3 — 261.63 Hz: n = 69 + 12 × log₂(261.63 ÷ 440) = 69 − 9 = 60 → C4 (middle C), 0 cents. Nine semitones below A4 — nine descending steps: A→G♯ (1), G♯→G (2), G→F♯ (3), F♯→F (4), F→E (5), E→D♯ (6), D♯→D (7), D→C♯ (8), C♯→C (9) — landing on C.

How to Use This Frequency-to-Note Converter

1. Enter the frequency in Hertz in the input box (any value from 20 to 20,000 Hz).
2. Set the A4 reference if your ensemble does not tune to 440 — orchestras often use 441–443 Hz, Baroque groups 415 Hz.
3. Try a quick button for common cases: C4, A4, C5, A5, the 1000 Hz test tone, or 60 Hz mains hum.
4. Press Convert to Note and read the result box: note name, octave, exact frequency, MIDI number, and cents deviation.
5. Check the cents bar below the result — the dot shows how sharp or flat the frequency sits versus the nearest note.

Reading Your Result

A440 Is Not Universal: The A4 Reference Problem

The 440 Hz standard (ISO 16, adopted 1955) is a convention, not a law of physics — and working musicians break it constantly. Many European orchestras tune to 441–443 Hz for extra brilliance; Baroque ensembles playing period instruments use A415 Hz (a semitone flat); some American orchestras sit at 440–442 Hz.

This matters for conversion: at an A442 reference, a measured 440 Hz is not A4 — it is A4 at −7.85 cents. That is why this converter lets you set the A4 reference between 430 and 450 Hz. If you are transcribing an orchestra recording and every note reads a few cents flat, the ensemble probably was not at 440 — adjust the reference until the deviations center on zero.

The MIDI Bridge: One Formula for Your DAW

The formula n = 69 + 12 × log₂(f ÷ 440) is the same math every DAW uses to turn frequencies into piano-roll notes — 69 is simply MIDI's number for A4. Going the other way, f = 440 × 2^((n − 69) ÷ 12) turns any MIDI note into its frequency.

Practical uses: convert a measured vocal pitch to a MIDI number and quantize it; compute the exact Hz for a synth oscillator from a MIDI note; or check a sample's tuning — a 808 kick reading MIDI 36.4 is C1 plus 40 cents, audibly sharp. The note-to-frequency converter runs this direction for any named note.

Middle C Confusion: C4 vs C3

Middle C is 261.63 Hz. In scientific pitch notation — the standard used in acoustics and by this converter — that is C4. But Yamaha keyboards and many DAWs label the same key C3, because Yamaha numbers octaves starting one lower. Roland and others follow the scientific C4.

The frequencies never disagree — only the labels do. When this converter says C4 and your keyboard says C3, you are looking at the same 261.63 Hz. If you collaborate across gear, always confirm frequencies, not octave numbers.

The 60 Hz Hum Trick: Identifying Mystery Buzzes

Not every frequency you measure is musical. In the US, a steady 60 Hz hum (50 Hz in Europe and most of Asia) leaking into a recording is mains hum from the electrical grid — it converts to roughly B1, but no musician played it. Ground loops, dimmers, and cheap power supplies are the usual suspects.

Use the converter as a detective: measure the hum's frequency with the pitch detector, convert it here, and if it lands on 60 Hz (or its harmonics at 120, 180, 240 Hz), reach for a ground-lift or a notch filter — not a tuner. Musical notes rarely sit exactly on these values.

Limitations

• 12-tone equal temperament only. Just-intonation intervals, maqams, and other tuning systems need their own mapping.
• One frequency in, one note out. Chords and polyphonic audio contain many frequencies — this tool reads single pitches; use the pitch detector on isolated lines.
• Extreme lows and highs blur. Below ~30 Hz most people feel rather than hear pitch; above ~5 kHz, note identification gets unreliable.
• Timbre can fool the math. A strongly inharmonic sound (bells, for instance) may convert to a note that does not match what you hear.

Frequency-to-Note vs Other Pitch Tools

Frequently Asked Questions