A440 is the international standard for concert pitch (ISO 16, 1955), setting the note A above middle C to exactly 440 Hz. All other note frequencies are calculated relative to this reference.

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Equal Temperament Frequency Chart

The complete reference table of all 120 musical notes from C0 to B9 in 12-tone equal temperament. Frequencies in Hz, MIDI numbers, period, wavelength, and click-to-play audio for every note.

A4 Reference

Hz

415440450

A4 = 440.0 Hz

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Interactive Piano (C4 – B5)

Complete Frequency Table

Note	Octave	Frequency (Hz)	MIDI #	Period (ms)	Wavelength (m)	Play	Copy

Equal Temperament Formula

Frequency Formula

f = 440 × 2^{(n − 69) / 12}

Where f is the frequency in Hz, 440 is the A4 reference frequency, n is the MIDI note number (A4 = 69), and the exponent divides the octave into 12 equal semitones. Each semitone multiplies the frequency by 2^1/12 ≈ 1.05946.

Octave Doubling

f(octave up) = f × 2

Moving up one octave exactly doubles the frequency. A4 = 440 Hz, A5 = 880 Hz, A3 = 220 Hz. This logarithmic relationship means each octave spans the same perceptual interval despite covering a larger range of Hz values.

Semitone Ratio

r = 2^1/12 ≈ 1.059463

In equal temperament, the ratio between any two adjacent semitones is constant: the 12th root of 2. This means all keys and intervals are equally "in tune" (or equally "out of tune" compared to just intonation), enabling free modulation between keys.

MIDI Number to Note

note = (n mod 12), octave = floor(n/12) − 1

MIDI note numbers run from 0 to 127. Middle C (C4) is MIDI 60. The note name is determined by the remainder when dividing by 12; the octave by the quotient minus 1. This chart covers MIDI 12 (C0) through 131 (B9).

How to Use This Chart

Find any note's frequency — Scroll or search the table to find the exact Hz value for any note from C0 (16.35 Hz) to B9 (15,804.27 Hz). Use the search box to jump directly to a note name, frequency, or MIDI number.
Adjust the A4 reference — Use the slider to change A4 from the standard 440 Hz to any value between 415 and 450 Hz. All 120 frequencies recalculate instantly. Use 432 Hz for "Verdi tuning," 415 Hz for Baroque pitch, or 443 Hz for many European orchestras.
Listen and verify — Click the Play button on any row to hear the note as a pure sine tone. The currently playing note glows in the table and on the piano keyboard. Use this to verify tuning, test speaker response, or train your ear.

Understanding the Equal Temperament Chart

Equal temperament (specifically 12-tone equal temperament or 12-TET) is the most widely used tuning system in Western music. It divides the octave into 12 equal semitones, where each semitone has a frequency ratio of 2^1/12. This system was adopted because it allows music to be played in any key with the same relative tuning, enabling free modulation between keys.

The A4 = 440 Hz Standard

The international standard pitch, adopted by ISO in 1955, sets A4 (the A above middle C) to exactly 440 Hz. From this single reference point, every other note's frequency is mathematically determined. However, this standard is not universal: many orchestras tune slightly higher (441-443 Hz) for a brighter sound, Baroque ensembles often use A4 = 415 Hz, and some musicians advocate for A4 = 432 Hz.

Octave Doubling Principle

A fundamental property of musical pitch is that doubling a frequency raises it by exactly one octave. A3 = 220 Hz, A4 = 440 Hz, A5 = 880 Hz. This means low octaves (0-2) span only a few hundred Hz total, while high octaves (7-9) each span thousands of Hz. The human ear perceives pitch logarithmically, which is why equal-ratio spacing sounds "equal" to us.

MIDI Note Numbers

The MIDI (Musical Instrument Digital Interface) standard assigns integer numbers to notes. Middle C (C4) is MIDI 60, and each semitone increments by 1. This chart covers MIDI 12 (C0) through MIDI 131 (B9), encompassing the full range of a concert piano and beyond. MIDI note numbers provide a convenient integer index for any note in the system.

Frequently Asked Questions

What is equal temperament?

Equal temperament is a tuning system that divides the octave into 12 equal semitones. Each semitone has a frequency ratio of 2^(1/12), approximately 1.05946. This means every key sounds equally "in tune," unlike historical tuning systems (meantone, Pythagorean) where some keys sounded pure and others harsh. Nearly all modern Western music uses 12-tone equal temperament (12-TET).

What frequency is middle C?

Middle C (C4) is approximately 261.626 Hz in standard A440 tuning. It is MIDI note number 60. Middle C sits near the center of the piano keyboard and the treble and bass clefs in musical notation. It is the most commonly referenced note in music education.

What is A440?

A440 (also written A4 = 440 Hz) is the international standard for concert pitch, adopted by ISO 16 in 1955. It means the note A above middle C vibrates at exactly 440 cycles per second. All other note frequencies are calculated relative to this reference. Tuning forks, electronic tuners, and orchestras worldwide use A440 as their reference, though some orchestras tune to 441, 442, or 443 Hz.

What is the frequency range of a piano?

A standard 88-key piano spans from A0 (27.5 Hz) to C8 (4186.01 Hz). This covers just over 7 octaves. The lowest note approaches the lower limit of human pitch perception (~20 Hz), while the highest note is well within the audible range. This chart extends beyond the piano range, covering C0 (16.35 Hz) to B9 (15,804.27 Hz).

Why do some musicians use A432 instead of A440?

Some musicians prefer A4 = 432 Hz, claiming it sounds warmer or more natural. Historically, concert pitch varied widely: Baroque pitch was around 415 Hz, Classical era around 430 Hz, and pitch has gradually risen over centuries. While there is no scientific evidence that 432 Hz has special physical properties, it remains a popular alternative tuning. This chart lets you set any A4 reference between 415 and 450 Hz to see all frequencies at your preferred tuning.

How are MIDI note numbers assigned?

MIDI note numbers are integers from 0 to 127. Middle C (C4) is MIDI 60, and each semitone up or down adds or subtracts 1. A4 (440 Hz) is MIDI 69. The formula to convert MIDI number to frequency is: f = 440 * 2^((n-69)/12). This chart covers MIDI 12 (C0) through MIDI 131 (B9), with MIDI 12-131 representing the 120 notes of the 10-octave range.

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