Note to Frequency Converter: Exact Hz for Any Note

A note-to-frequency converter turns any musical note — like A4 or C♯3 — into its exact vibration rate in hertz (Hz). Under the standard A440 tuning, middle C (C4) is 261.63 Hz, and the frequency doubles with every octave up. This free calculator converts any note and octave to Hz instantly, and also reports the MIDI number, wavelength, and wave period.

Key Takeaways

• Every note has one exact frequency under 12-tone equal temperament: A4 = 440 Hz, middle C (C4) = 261.63 Hz.
• Frequency doubles every octave: A3 = 220 Hz, A4 = 440 Hz, A5 = 880 Hz.
• The conversion formula is f = A4 × 2^((m − 69)/12), where m is the note's MIDI number (A4 = 69).
• Written notes on transposing instruments — trumpet, saxophone, horn — sound at different concert frequencies; convert the concert pitch, not the written note.

What Is Note-to-Frequency Conversion?

Musicians think in note names; synthesizers, EQ plug-ins, and signal generators think in hertz. Note-to-frequency conversion is the bridge between the two. A producer who wants the sub-bass to sit on D2 needs 73.42 Hz; an engineer treating a room mode at 65 Hz is targeting C2.

This page's mapping assumes 12-tone equal temperament (12-TET), the tuning system behind pianos, guitars, and every DAW piano roll. In 12-TET, each semitone multiplies the frequency by the same ratio, so one formula converts every note in every octave.

How This Calculator Works

This calculator takes three inputs — a note name (C through B, with sharps), an octave number (0–8), and the A4 reference frequency (default 440 Hz). It counts how many semitones the note sits from A4, then applies the equal-temperament formula to get the frequency. From that one number it derives the rest: the MIDI note number (69 plus the semitone count), the wavelength (343 ÷ frequency, the speed of sound at 20°C), the wave period (1000 ÷ frequency, in milliseconds), and the frequency one octave below (frequency ÷ 2).

Methodology: the All Octaves table repeats the calculation for octaves 0 through 8, and the Play button renders the result as a pure sine tone through the Web Audio API. Every readout comes from the same frequency value, so the outputs always agree — with each other and with any DAW or tuner using the same standard. Last reviewed: October 2026.

The Formula and a Worked Example

One formula converts every note, in every octave, at any reference pitch:

Here m is the note's MIDI number (A4 = 69, middle C = 60, each semitone = ±1), and A4 is the reference pitch, usually 440. Each semitone multiplies the frequency by 2^(1/12) ≈ 1.059463094, and twelve semitones multiply it by exactly 2 — the octave.

Worked example — E4, the guitar's high E string. E4 is MIDI 64, so f = 440 × 2^((64 − 69)/12) = 440 × 2^(−5/12) = 440 × 0.749154 = 329.63 Hz. Wavelength: 343 ÷ 329.63 = 1.04 m (about 3.41 ft). Period: 1000 ÷ 329.63 = 3.03 ms. One octave below: E3 = 329.63 ÷ 2 = 164.81 Hz. Try it above — every number will match.

One more note on sharps: F♯4 and G♭4 are the same piano key, so they share one frequency (369.99 Hz). The widget's sharp buttons give each enharmonic pair a single value — spelling differs for notation, not for physics.

How to Use This Calculator

1. Select a note: click one of the 12 buttons (C through B). The sharp buttons (C♯, D♯, F♯, G♯, A♯) give the same frequencies as their flat equivalents.
2. Select an octave: 0 is sub-bass territory, 4 is the middle register, 8 is the extreme top. Middle C is C4.
3. Set the A4 reference: leave it at 440 Hz, or use a quick standard — 432, 440, 442, or 444 Hz. Match the pitch your ensemble tunes to.
4. Read the result box: the large number is the frequency in Hz; below it are the MIDI number, wavelength, period, and the frequency one octave down.
5. Press Play This Note: hear the exact pitch as a sine tone — useful for tuning by ear.
6. Check the All Octaves table: see the same note at every octave, each doubling in frequency, and pick the register you need.

Reading Your Result

Wavelength displays in meters; multiply by 3.281 for feet (C4's 1.31 m wave is about 4.30 ft). If instead you measured a frequency and want its note name, run it through the reverse frequency-to-note converter.

Transposing Instruments: Convert the Concert Pitch, Not the Written Note

Note-to-frequency charts assume concert pitch — the pitch you actually hear. But written notes on transposing instruments sound at a different pitch, so converting the note on the page gives the wrong frequency. A B♭ trumpet is the classic example: its written C sounds a major second lower, as B♭. So a trumpet part marked C4 does not produce 261.63 Hz — it produces concert B♭3 at 233.08 Hz. The rule: shift the written note down by the instrument's interval first, then convert the resulting concert pitch. The transpose calculator handles the interval math.

Why do these instruments transpose at all? Many wind instruments sound best built in certain keys, and their "home" scale is always written as C — so the instrument is named for the concert pitch its written C produces (Music Theory Academy).

Why A Is 440 Hz: A Short History of Pitch Inflation

440 Hz is a 20th-century compromise after centuries of pitch drifting upward. In the Baroque era, A sat around 415 Hz, nearly a semitone flat of today; by the 1800s, opera houses pushed pitch higher for brilliance — one La Scala fork reached 451 Hz.

France pushed back first: a law in 1859 fixed A at 435 Hz, the diapason normal. An 1834 Stuttgart conference had already recommended 440 Hz. The modern standard came from a 1939 London conference, which first considered 439 Hz but switched to 440 — because 439 is a prime number and hard to reproduce precisely in a laboratory. The ISO adopted 440 in 1955 as ISO 16.

The drift never fully stopped: orchestras kept creeping sharp for brightness, and Highland pipe bands sit near 470–480 Hz — close to B♭. Early-music ensembles still perform at A415, so a Baroque score's A4 converts to 415 Hz, not 440: set this calculator's A4 box accordingly. (Source: Wikipedia — Concert pitch.)

Tuning Forks: The Original Note-to-Frequency Reference

Before apps, musicians carried a piece of steel stamped with a frequency. The tuning fork was invented in 1711 by British musician John Shore, and it vibrates almost purely at its fundamental — which is why orchestras and choirs trusted it as their reference.

The standard fork is A440, but physics labs keep forks at 256, 512, and 1024 Hz from the "scientific pitch" system. Proposed by Joseph Sauveur in 1713 and promoted by Giuseppe Verdi in the 19th century, scientific pitch sets middle C to exactly 256 Hz, which puts A at 430.54 Hz — mathematically tidy, since every C is a power of two (Wikipedia — Scientific pitch).

To use one: strike an A440 fork and hold it near your guitar's A string. The beats between fork and string slow as the string approaches 440 Hz and vanish when it matches — a physical note-to-frequency check with no batteries required.

Open-String Frequencies: Standard Tunings in Hz

String players tune open strings to fixed frequencies — match them on a tuner, or dial them into a synth.

Guitar values match published string-manufacturer tension charts, and the rest follow the same equal-temperament math this calculator uses. For hands-on tuning, use the guitar tuner.

Fine-Tuning With Cents: Turning Small Offsets Into Hz

Tuners measure small errors in cents — 100 per semitone. To turn a cent reading into a target frequency, multiply the note's frequency by 2^(cents/1200).

A tuner reading of +5 cents on A4 means the target is 440 × 2^(5/1200) = 441.27 Hz. An A442 orchestra plays about +7.85 cents sharp of 440 — enter 442 in this page's A4 box. For the distance between two measured frequencies, see the cents calculator.

Limitations

• 12-tone equal temperament only. Just intonation, meantone, maqam, and other tuning systems map the same note names to different frequencies.
• Enharmonic equivalents share one frequency. C♯4 and D♭4 are both 277.18 Hz here, though notation treats them differently.
• Wavelength assumes 343 m/s at 20°C. Real rooms run warmer or colder, which shifts true wavelengths slightly.
• Octave numbers follow scientific pitch notation (middle C = C4); some keyboards and DAWs label the same key C3.
• Tone playback is a pure sine wave. Real instruments stack harmonics on top of the fundamental — see the harmonic series calculator for what those add.

Note-to-Frequency vs Other Pitch Tools

Frequently Asked Questions