What frequency is A4?

A4 is 440 Hz in standard tuning. This is the internationally agreed pitch reference (ISO 16). Some orchestras use A4 = 442 Hz for a brighter sound, and some alternative tuning proponents use 432 Hz.

How is note frequency calculated?

Using 12-tone equal temperament: f = 440 × 2^((n−69)/12), where n is the MIDI note number. A4 = MIDI 69. Each semitone multiplies the frequency by the twelfth root of 2 (≈1.05946).

What is Middle C frequency?

Middle C is C4 (MIDI note 60) and has a frequency of approximately 261.63 Hz in standard A440 tuning. It sits one octave below C5 (523.25 Hz) and one above C3 (130.81 Hz).

What is a cent in music?

A cent is 1/100th of a semitone. There are 1200 cents in an octave. Cents are used to measure tiny pitch deviations — a deviation of ±5 cents is barely audible; ±20 cents is clearly out of tune.

Note Frequency Calculator

Convert musical notes to frequency in Hz using equal temperament. Look up any MIDI note, find the nearest note from a frequency, compare octaves, and explore harmonics.

MIDI Note Number (0–127) ?

A4 Reference (Hz) ?

Frequency (Hz)

—

Note Name —

Octave —

Extended More scenarios, charts & detailed breakdown ▾

Note

Octave

A4 Reference (Hz)

Frequency (Hz)

—

MIDI Note # —

Wavelength (cm) —

Professional Full parameters & maximum detail ▾

MIDI Note (0–127)

A4 Reference (Hz)

Fundamental

Frequency (Hz) —

Note Name —

Acoustics

Wavelength in Air (cm) —

Period (ms) —

Harmonics

2nd Harmonic (Hz) —

3rd Harmonic (Hz) —

4th Harmonic (Hz) —

How to Use This Calculator

Enter a MIDI Note Number (A4 = 69, Middle C = 60) to get its frequency in Hz.
Adjust the A4 Reference to use alternate tuning (432, 440, 442, or 444 Hz).
Use the Hz → Note tab to find which note matches a given frequency.
The Octave Comparison tab shows the same note across all 9 octaves.

Formula

f = A4_ref × 2^{(n − 69) / 12}

Where n = MIDI note number (A4 = 69, each semitone = ±1).

Example

Find frequency of C4 (Middle C): MIDI 60, A4 = 440 Hz → f = 440 × 2^(60−69)/12 = 440 × 2^−0.75 ≈ 261.63 Hz.

Frequently Asked Questions

A4 is 440 Hz in standard tuning. This is the internationally agreed pitch reference (ISO 16). Some orchestras use A4 = 442 Hz for a brighter sound, and some alternative tuning proponents use 432 Hz.
Using 12-tone equal temperament: f = 440 × 2^((n−69)/12), where n is the MIDI note number. A4 = MIDI 69. Each semitone multiplies the frequency by the twelfth root of 2 (≈1.05946).
Middle C is C4 (MIDI note 60) and has a frequency of approximately 261.63 Hz in standard A440 tuning. It sits one octave below C5 (523.25 Hz) and one above C3 (130.81 Hz).
A cent is 1/100th of a semitone. There are 1200 cents in an octave. Cents are used to measure tiny pitch deviations — a deviation of ±5 cents is barely audible; ±20 cents is clearly out of tune.

Related Calculators

Sources & References (5) ▾

Music Acoustics — Note Frequencies — Stanford CCRMA
Equal Temperament and Pitch Standards — MIT Music & Theater Arts
Pitch and Frequency in Music Theory — Berklee Online
Acoustical Society of America — Musical Acoustics — Acoustical Society of America
ISO 16: Acoustics — Standard Tuning Frequency — ISO