Music Note Frequency Converter

Music Note Frequency Converter — Hz ↔ Note Names with Piano Playback

Type a note name and see its frequency in Hertz, or enter a frequency and find the closest note plus the cents off pitch. The interactive piano lets you click any key to hear it, the tuning reference adjusts A4 (default 440 Hz, with 432, 415, and 466 Hz presets for alternative and historical tunings), and the temperament selector switches between equal temperament, just intonation, and Pythagorean. Useful for instrument tuning, audio engineering, music composition, and ear training.

What is the formula that converts MIDI note numbers to frequency?

Every note in 12-tone equal temperament (12-TET, the system used by virtually all Western instruments tuned today) sits on an exponential grid:

**f = A4 × 2^((m − 69) / 12)**

where:
- **f** is the frequency in Hertz
- **A4** is your tuning reference (default 440 Hz)
- **m** is the MIDI note number (0 to 127; A4 = 69, middle C = 60, the lowest piano key A0 = 21)

The formula works because an octave is exactly a 2:1 frequency ratio, and 12-TET divides that octave into 12 equal logarithmic steps. So each semitone multiplies frequency by 2^(1/12) ≈ 1.05946.

With A4 = 440 Hz:
- C4 (middle C, MIDI 60) = 440 × 2^((60−69)/12) = 440 × 2^(−9/12) ≈ 261.63 Hz
- A5 (MIDI 81) = 440 × 2^(12/12) = 880 Hz (one octave up)
- C8 (MIDI 108) ≈ 4186.01 Hz (top piano key)

The inverse — frequency to MIDI — uses logarithms: **m = 69 + 12 × log₂(f / A4)**. The result is usually fractional; rounding to the nearest integer gives the closest standard pitch, and the leftover decimal × 100 gives the cents off.

Why does A4 = 432 Hz exist and is it 'better' than 440?

A4 = 440 Hz was adopted as the international standard in 1939 at a conference in London, and reaffirmed by ISO 16:1975. Before then, tuning varied widely: 19th-century orchestras drifted upward in pitch (a phenomenon called "pitch inflation") and different cities used different references. Verdi famously campaigned for A4 = 432 Hz in the 1880s, hoping to standardize a lower, softer pitch for opera singers.

**A4 = 432 Hz** is popular today in some new-age, healing, and alternative-music circles. Claims that it's "the natural frequency of the universe," "resonates with Schumann resonances," or "matches sacred geometry" have no acoustic basis. There's no peer-reviewed evidence it sounds objectively better.

That said, 432 Hz is a real tuning choice and changes the character slightly — instruments tuned 8 cents lower sound a touch warmer and have slightly lower vocal demands. Some film composers and electronic producers use it for artistic preference, not science.

**A4 = 415 Hz** is the Baroque tuning (roughly half a semitone below modern A) — the standard for historically informed performances of Bach, Handel, Vivaldi.

**A4 = 466 Hz** is the "Chorton" or high choir pitch sometimes used by Bach's church organs in Leipzig.

All four presets are one click away in this tool.

What are equal temperament, just intonation, and Pythagorean?

These are systems for dividing the octave into smaller intervals. They all agree that an octave is exactly 2:1; they disagree on everything in between.

**Equal temperament (12-TET):** divides the octave into 12 equal logarithmic steps. Every semitone is the same width (2^(1/12) ≈ 1.0595). All intervals other than octaves are slightly out of tune compared to their simple integer ratios, but they're consistently out of tune in every key — so you can play in any key with the same character. This is what every piano, every guitar, every modern keyboard uses.

**Just intonation:** tunes intervals to simple integer ratios. A major third is exactly 5:4, a perfect fifth is exactly 3:2, a major sixth is 5:3. The intervals sound pure and "beat-free," but only in one key — modulating to a different key sounds out of tune. Used in a cappella choirs, traditional Indian music, drone music, and barbershop quartets.

**Pythagorean:** built entirely from the 3:2 ratio (perfect fifth), stacking fifths to derive all 12 notes. Perfect fifths sound flawless; major thirds are noticeably wider than just intonation (81:64 vs 5:4). Common in medieval music and some early-music ensembles. The 'Pythagorean comma' — a wraparound error of about 23.5 cents — is the gotcha that made 12-TET necessary.

For most modern Western music, equal temperament is the right default. The other two are mainly relevant for specialized historical or world music.

How do I read 'cents off'?

Cents are a logarithmic unit of pitch interval. By definition, 100 cents = 1 semitone, so an octave = 1200 cents.

When you enter a frequency that's not exactly a 12-TET note, the calculator finds the nearest note and tells you how far off that frequency is in cents:

- **+50.0 cents** = a quarter-tone above. You're equidistant between two notes; tuners usually flag this as a hard call.
- **±10 cents** = noticeable to a trained ear. The pitch sounds slightly sharp/flat. A guitarist would re-tune.
- **±5 cents** = barely perceptible to most listeners; orchestras consider this "in tune."
- **±1 cent** = beyond the just-noticeable difference; effectively perfect for non-electronic music.

Formula: **cents = 1200 × log₂(actual / target)**.

Example: a tuner reads 442 Hz when you played A4 (target 440 Hz). Cents = 1200 × log₂(442/440) = 1200 × log₂(1.00455) ≈ +7.85 cents. You're 8 cents sharp — a clearly audible amount; tune down.

This is how every electronic tuner works.

Why does scientific pitch notation use C4 for middle C?

Scientific pitch notation (SPN) labels each octave with a number and uses the letter-then-number form: **C4**, **D4**, **F#5**, etc. The convention is:

- The octave number changes at C, not at A. So B3 is followed by C4 (one semitone higher).
- **C4 is middle C** on a piano — the C nearest the center of the keyboard.
- A4 is the next A above middle C, three white keys to the right.
- The 88-key piano runs from A0 (lowest) to C8 (highest).
- MIDI note 0 corresponds to C-1 (8.18 Hz, below human hearing); MIDI 127 is G9 (12,544 Hz, above most adults' hearing). Standard piano range is MIDI 21–108.

This differs from some older systems:

- **Helmholtz notation** (used in 19th-century music theory) labels middle C as c′, then c″ for C5, and lowercase letters with no marks for the octave below middle C. This calculator does not use Helmholtz.
- **Casio/Yamaha keyboards** sometimes label middle C as C3 instead of C4, shifting their octave numbering one down. This tool uses the SPN convention (middle C = C4) because it matches MIDI and most modern theory texts.

What practical use does this tool have for tuning?

A few:

1. **Tuning by ear with a reference tone.** Click an A4 key on the piano, listen carefully, and tune your instrument to match. The Play button uses a clean sine wave so it's easy to hear beats when you're close.
2. **Designing audio filters.** A 1 kHz low-pass cutoff is just over a major seventh above C6 (1046.5 Hz). Knowing the exact note frequencies helps when you're EQ'ing a guitar: the fundamental of low E is 82.4 Hz, so a 60 Hz high-pass barely touches it.
3. **MIDI mapping.** When working with software synthesizers, the MIDI note number (also shown by this tool) is the value sent over the wire. Useful when patching samplers or writing MIDI scripts.
4. **Composition reference.** Knowing that the human voice covers roughly C3 to C6 (130–1046 Hz fundamental) helps when writing for choir or assigning parts.
5. **Spectrum analysis.** If you see a peak at 880 Hz in an audio spectrum, this tool tells you instantly: that's A5, two octaves above A3.
6. **Education.** Visualizing the exponential relationship between MIDI numbers and Hz makes the formula click in a way no equation alone can.

Why does the sound work in some browsers but not others?

The Play button uses the Web Audio API, which is supported in every modern browser (Chrome, Firefox, Safari, Edge) on desktop and mobile. The only catch is that browsers don't let pages start audio without a user gesture — so the first time you click Play after the page loads, a brief silent gap may occur as the audio context resumes from its suspended state.

If no sound plays:

1. Check your system volume isn't muted, and your browser tab isn't muted (right-click the tab → Unmute).
2. Try a different browser. Safari sometimes blocks AudioContext on iOS if the page is in low-power mode.
3. Some browser extensions (specifically tracker-blockers) occasionally interfere with Web Audio. Try disabling them on this domain.
4. iOS Safari requires the device's silent switch be off for media playback. This is a system-level restriction beyond the browser's control.

The oscillator is a pure sine wave at the requested frequency. It plays for about 600 ms with a soft attack and decay envelope to avoid clicks. No samples or external audio files are loaded — everything is synthesized in the browser, so the tool works offline once the page has loaded.

Is this calculator private?

Yes. Every calculation and every Play press happens in your browser:

- The note ↔ frequency math is straightforward floating-point arithmetic — no remote API is called.
- The piano renders via plain DOM elements; clicking a key triggers a local Web Audio oscillator.
- No telemetry of which notes you played, which tunings you selected, or which frequencies you entered.
- The page shares the site's normal assets (Bootstrap, icons) but contacts no third-party audio or music service.

Verify by opening DevTools → Network and watching while you click around — no requests fire when you type a note, select a tuning, or play a tone. This means the tool works offline (after first page load) and any note sequence you experiment with stays on your device.

Key Features

• Bidirectional conversion: note name ↔ frequency in Hz
• Interactive 4-octave piano keyboard with click-to-play
• Web Audio sine-wave playback for any note or frequency
• Tuning reference: A=440 (modern), A=432 (alternative), A=415 (Baroque), A=466 (Chorton)
• Custom A4 frequency input (200–600 Hz range)
• Temperament options: 12-TET (equal), Just Intonation, Pythagorean
• Notation modes: sharp (C, C#, D), flat (C, Db, D), or solfege (Do, Do#, Re)
• Cents-off display for non-standard frequencies
• MIDI note number shown alongside scientific pitch notation
• Octave start selector for piano (2 to 5)
• Reference table for common notes (low E guitar, middle C, concert A, etc.)
• Auto-formats output in Hz with appropriate decimal precision
• Copy frequency or note name to clipboard
• Works offline after first load
• 100% client-side — your music stays in your browser