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. Frequencies are continuous — 437.2 Hz is a real sound — but note names are twelve discrete slots per octave. The converter finds the nearest slot and reports how far off you are in cents, so a tuner, a DAW, and a musician all agree on what they hear.

Key Takeaways

• 440 Hz = A4 under the ISO 16 concert-pitch standard — but orchestras and period ensembles tune elsewhere, so the A4 reference on this page is adjustable.
• n = 69 + 12 × log₂(f ÷ 440) gives the MIDI note number; the note name comes from the rounded value.
• Cents deviation shows how sharp (+) or flat (−) the frequency sits against the nearest note.
• Middle C is C4 (261.63 Hz) in scientific pitch notation; some keyboards label the same key C3.
• A steady 60 Hz buzz in the US (50 Hz in Europe) is mains hum from the power grid — fix the grounding, not the tuning.

How This Converter Works

This converter maps any frequency to the 12-tone equal-tempered chromatic scale with 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 and adjusts from 430–450 Hz, because working ensembles do not all tune to 440. Results assume 12-tone equal temperament. The formula reproduces the standard 88-key piano values exactly — A0 at 27.50 Hz, middle C at 261.63 Hz, C8 at 4186.01 Hz. 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. Perfectly in tune.

Worked example 2 — 432 Hz: n = 69 + 12 × log₂(432 ÷ 440) = 69 − 0.3177 = 68.6823. The nearest whole number is 69, so the note is A4 at −31.77 cents — a flat A, about one-third of a semitone low. The cents calculator shows the same interval math.

Worked example 3 — 261.63 Hz: n = 69 + 12 × log₂(261.63 ÷ 440) = 69 − 9.0000 = 60 → C4 (middle C), 0 cents — nine semitones below A4.

How to Use This Frequency-to-Note Converter

1. Enter the frequency in the input box — any value from 20 to 20,000 Hz.
2. Set the A4 reference (430–450 Hz) when your ensemble does not tune to 440 — orchestras often use 441–443 Hz.
3. Tap 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, and cents deviation.
5. Read the cents bar under the result — the dot shows how sharp or flat the frequency sits against the nearest note.

Reading Your Result

The midpoint rule: a frequency belongs to whichever note sits within ±50 cents of it. Near that boundary, small measurement noise flips the answer — 60 Hz reads B1 at −49.4 cents, just 0.6 cents from tipping toward A♯1. Treat any reading beyond ±45 cents as "between notes" and measure the source again before you trust the name.

Common Frequencies and Their Nearest Notes

Round numbers rarely land exactly on notes. The table converts the frequencies people most often measure or type — test tones, mains hum, round oscillator settings — at the standard A4 = 440 Hz reference.

Octaves repeat the same cents value: 100, 200, and 400 Hz each sit +35.0 cents sharp of G, because doubling a frequency moves it to the same note name one octave up, at the identical distance from that note.

A440 Is Not Universal: The A4 Reference Problem

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

The reference shifts every conversion. At an A442 reference, a measured 440 Hz is not A4 — it is A4 at −7.85 cents (1200 × log₂(440 ÷ 442)). That is why this converter sets the A4 reference between 430 and 450 Hz. When you transcribe an orchestra recording and every note reads a few cents flat, the ensemble was probably not at 440 — adjust the reference until the deviations center on zero.

The MIDI Bridge: One Formula for Your DAW

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; check a sample's tuning — an 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. Yamaha keyboards and many DAWs label the same key C3, because Yamaha numbers octaves one lower. Roland and most notation software 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. Confirm frequencies, not octave numbers, when you collaborate across gear.

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) bleeding 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 with the pitch detector, convert it here, and when 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 map the same frequencies to different notes.
• One frequency in, one note out. Chords and polyphonic audio hold many frequencies — this tool reads single pitches; use the pitch detector on isolated lines.
• Extremes blur. Below ~30 Hz most people feel rather than hear pitch; above ~5 kHz, note naming turns unreliable.
• Timbre fools the math. Strongly inharmonic sounds (bells are the classic case) can convert to a note that does not match what you hear.

Frequency-to-Note vs Other Pitch Tools

Frequently Asked Questions