🎵 Musical Note Pitch to Audio Frequency (Hz) Finder

Convert musical note pitch and octave numbers to equal temperament frequency in Hertz (Hz), MIDI key number, and sound wavelength. With audio tone playback.

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Note

Octave

Concert pitch A4 (Hz)

440.00 Hz

MIDI note number69

Period2.273 ms

Wavelength in air at 20 °C78.0 cm

Octave above / below880.00 Hz / 220.00 Hz

Twelve-tone equal temperament: every semitone is the twelfth root of two, about 1.0595, so twelve of them make exactly a doubling. That is a compromise — no interval except the octave is in pure whole-number ratio, and an equal-tempered major third is about 14 cents sharp of the pure one. It is what makes a piano playable in every key.

What Musical Note Pitch to Audio Frequency (Hz) Finder Does

Every note in modern Western tuning is a fixed number of hertz, worked out from one reference: A above middle C at 440 Hz. From there, each semitone multiplies the frequency by the twelfth root of two, about 1.05946, so twelve of them land exactly on a doubling — the octave.

That system is twelve-tone equal temperament, and it is a deliberate compromise. Every interval except the octave is slightly out of pure whole-number ratio: an equal-tempered major third sits about 13.7 cents sharp of the pure 5:4 that actually beats cleanly. The payoff is that every key sounds the same, which is what makes a piano playable in all of them.

The reverse direction is the tuning one. Given a frequency you have measured, the nearest note and the cents away from it is what a tuner shows you. A semitone is 100 cents by definition, and most listeners stop hearing an error on a sustained note somewhere around five cents — which is why tuners draw a green zone rather than demanding zero.

A440 is a convention, not a law. Baroque ensembles commonly play at 415 Hz, almost exactly a semitone flat at −101 cents, and many European orchestras tune to 442 or 443 for a brighter sound. Changing the reference shifts every note by the same number of cents.

How to Use Musical Note Pitch to Audio Frequency (Hz) Finder

Select musical note (C through B) and octave number (0 to 8)
Review calculated frequency in Hertz (Hz) and wavelength in air
Click Play Pure Audio Sine Tone to hear the exact pitch

Formula Used by Musical Note Pitch to Audio Frequency (Hz) Finder

Note to frequency, and frequency back to note

f = A₄ · 2^((m − 69) ÷ 12) · m = 69 + 12·log₂(f ÷ A₄) · cents = 1200·log₂(f₁ ÷ f₂)

m: MIDI note number — A4 is 69, middle C is 60, and each semitone is one step
A₄: the reference pitch, 440 Hz by modern convention
cents: a hundredth of an equal-tempered semitone; the standard unit for tuning error

Worked example

Middle C, which is MIDI 60, at A4 = 440.

Semitones from A4: 60 − 69 = −9
f = 440 × 2^(−9/12) = 440 × 0.59460

Result: 261.63 Hz. Going the other way, a measured 445 Hz is 19.6 cents sharp of A4 — audible on a sustained note, and roughly where an orchestra tuned to 442 would sit against a 440 reference.

Reference frequencies at A4 = 440 Hz

Note	Frequency	MIDI
C2	65.41 Hz	36
E2 — guitar low E	82.41 Hz	40
A2 — guitar A	110.00 Hz	45
D3 — guitar D	146.83 Hz	50
G3 — guitar G	196.00 Hz	55
B3 — guitar B	246.94 Hz	59
C4 — middle C	261.63 Hz	60
E4 — guitar high E	329.63 Hz	64
A4 — concert pitch	440.00 Hz	69
C5	523.25 Hz	72
A5	880.00 Hz	81

Tuning references you will meet

Cents relative to A440.

Reference	A4	Difference	Used by
Baroque pitch	415 Hz	−101.3 cents	Historically informed performance — nearly a semitone down
Classical pitch	430 Hz	−39.8 cents	Some period ensembles
Concert pitch	440 Hz	0	The international standard
Continental	442 Hz	+7.9 cents	Many European orchestras
Brighter continental	443 Hz	+11.8 cents	Some German and Austrian orchestras

Equal temperament against pure intervals

What the compromise costs. A positive figure means the equal-tempered interval is sharp of the pure one.

Interval	Pure ratio	Error in cents
Octave	2:1	0 — the only exact one
Perfect fifth	3:2	−2.0
Perfect fourth	4:3	+2.0
Major third	5:4	+13.7
Minor third	6:5	−15.6

How to Read Your Result

Five cents is roughly where it stops mattering

On a sustained tone most people cannot reliably hear an error below about five cents, though beating between two instruments makes far smaller differences obvious. That is why tuners show a tolerance band, and why two guitars can each read in tune and still sound wrong together.

Guitars are never quite in tune, by design

Frets are placed for equal temperament, so every chord is a compromise. The major third being nearly 14 cents sharp is why an open E major chord sounds slightly harsh, and why some players deliberately tune the G string a few cents flat.

The octave doubling makes checks easy

Every octave is exactly double, so 440 gives 880 and 220 without any calculation. If a frequency you have measured is close to double or half a note you know, you have the right note in the wrong octave — a common misreading on low bass notes, where tuners often jump an octave.

Wavelength matters for room acoustics

A4 at 440 Hz has a wavelength of about 78 cm in air. Low bass notes run to several meters, which is why they interact with room dimensions and why bass traps are large. The tool shows the wavelength alongside the frequency for that reason.

Limitations & Accuracy Notes

Twelve-tone equal temperament only. Just intonation, meantone, well temperaments and non-Western scales all place notes differently.
Frequencies are the mathematical ideal. Real instruments are inharmonic — piano strings in particular are stretched-tuned deliberately, so the top and bottom octaves are not exact multiples.
The wavelength figure assumes dry air at 20 °C. The speed of sound rises with temperature, so the value shifts a little in a hot or cold room.
Tone playback needs Web Audio, and the browser may require a click before it will produce sound.
This is not a microphone tuner — it does not listen. Enter a frequency you have measured elsewhere.

Frequently Asked Questions

What is the standard concert pitch frequency?

Modern Western concert pitch standardizes the note A in the 4th octave (A4) at exactly 440 Hz.

What is the formula for equal temperament note frequencies?

fn = A4 × 2^((n - 69) / 12), where n is the MIDI note number (C4 = 60, A4 = 69).

Why is A4 440 Hz?

It is the modern concert pitch standard and is largely a matter of agreed convention rather than acoustics. Historical tunings varied considerably — baroque ensembles commonly use 415 Hz — and some orchestras today tune slightly sharp of 440.

How are the other frequencies calculated?

By equal temperament: each semitone is the twelfth root of two times the one below, roughly 1.0595. Twelve of those multiplications double the frequency, which is exactly one octave.

What is the difference between equal temperament and just intonation?

Just intonation uses simple whole-number frequency ratios, which sound purer but only in one key. Equal temperament spreads the compromise evenly so every key is equally usable and none is perfectly in tune — the trade that made modern keyboard music possible.

What are cents?

A cent is one hundredth of a semitone, so an octave is 1,200 cents. It is the standard unit for describing small pitch differences, and around five cents is roughly where a trained listener starts to notice.

Why does the same note sound different on different instruments?

Because the fundamental frequency is only part of it. The pattern of overtones above it, and how the sound starts and decays, is what makes a violin and a flute at the same pitch immediately distinguishable.

Is anything sent to a server?

No. The frequencies are calculated in your browser.

References & Further Reading

MDN — Web Audio API — The oscillator used to generate the reference tone

By OnlineToolHubs Team • September 2026