What frequency is A4?

440 Hz by the modern standard, which is the reference this calculator uses by default. Some orchestras and historical instruments tune to 432, 435 or 442 Hz, so the reference is adjustable.

How is note frequency calculated?

From the tuning reference: frequency = A4 × 2^((MIDI note − 69) / 12). Every semitone multiplies frequency by the twelfth root of two, so the same formula covers the whole keyboard.

Why do I need note frequencies when mixing?

For targeted EQ. If a kick's fundamental is around 50 Hz, that is close to G1. Knowing the note lets you tune the kick to the track's key, or notch a resonance without guessing which band it is.

Does changing the tuning reference change the notes?

It changes every frequency proportionally while keeping the intervals identical. Tuning to 432 Hz makes everything about 32 cents flatter than 440 Hz, not differently spaced.

Free tool

Note Frequency Calculator

The exact frequency of any note in any octave, with an adjustable tuning reference and the MIDI note number.

Pure maths in your browser. No upload, no account.

Note

Octave

Middle C is C4.

Tuning reference

Frequency

440 Hz

MIDI note

Full note table

Frequencies in hertz at A4 = 440 Hz.

Note frequencies by octave
Note	Oct 0	Oct 1	Oct 2	Oct 3	Oct 4	Oct 5	Oct 6	Oct 7	Oct 8
C	16.35	32.7	65.41	130.81	261.63	523.25	1046.5	2093	4186.01
C#	17.32	34.65	69.3	138.59	277.18	554.37	1108.73	2217.46	4434.92
D	18.35	36.71	73.42	146.83	293.66	587.33	1174.66	2349.32	4698.64
D#	19.45	38.89	77.78	155.56	311.13	622.25	1244.51	2489.02	4978.03
E	20.6	41.2	82.41	164.81	329.63	659.26	1318.51	2637.02	5274.04
F	21.83	43.65	87.31	174.61	349.23	698.46	1396.91	2793.83	5587.65
F#	23.12	46.25	92.5	185	369.99	739.99	1479.98	2959.96	5919.91
G	24.5	49	98	196	392	783.99	1567.98	3135.96	6271.93
G#	25.96	51.91	103.83	207.65	415.3	830.61	1661.22	3322.44	6644.88
A	27.5	55	110	220	440	880	1760	3520	7040
A#	29.14	58.27	116.54	233.08	466.16	932.33	1864.66	3729.31	7458.62
B	30.87	61.74	123.47	246.94	493.88	987.77	1975.53	3951.07	7902.13

Frequencies below roughly 20 Hz and above 20 kHz are outside normal hearing, so the extreme octaves are shown for reference rather than as musical pitches. Going the other way? Use Frequency to Note.

Detail

How this works

Every frequency here comes from one formula: f = A4 × 2^((n − 69) / 12), where n is the MIDI note number. Change the reference and the whole grid shifts proportionally while the intervals stay identical.

This is the practical bridge between musical and technical language. Tuning a kick to the root of the track, notching a ringing resonance, or setting a filter to a note rather than a number all need the same conversion.

FAQ

Frequently asked questions

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