Converter Tools

Note Frequency Converter

Convert musical note names, MIDI numbers, and frequency in hertz in your browser. Custom A4 tuning, piano keyboard, cents offset, full MIDI table.

I want to enter a

Note name

Scientific pitch notation: C4 is middle C, A4 is the tuning reference. Sharps (#), flats (b), and Unicode accidentals (♯ ♭) are accepted.

Tuning reference (A4 in Hz)

Frequency decimals

Quick samples

Result

Octave 4

Frequency

440.00 Hz

MIDI note

Note (sharp)

Note (flat)

same as sharp

Period

2.2727 ms

Wavelength in air

77.95 cm

Reference

A4 = 440 Hz

Change the tuning reference above to retune every result.

Piano keyboard

Tap any key to load it

88 keys, A0 (MIDI 21) through C8 (MIDI 108). Scroll horizontally to reach the ends.

MIDI note table

All 128 MIDI notes at A4 = 440 Hz

MIDI	Note (sharp)	Note (flat)	Frequency (Hz)
0	C-1		8.18
1	C#-1	Db-1	8.66
2	D-1		9.18
3	D#-1	Eb-1	9.72
4	E-1		10.30
5	F-1		10.91
6	F#-1	Gb-1	11.56
7	G-1		12.25
8	G#-1	Ab-1	12.98
9	A-1		13.75
10	A#-1	Bb-1	14.57
11	B-1		15.43
12	C0		16.35
13	C#0	Db0	17.32
14	D0		18.35
15	D#0	Eb0	19.45
16	E0		20.60
17	F0		21.83
18	F#0	Gb0	23.12
19	G0		24.50
20	G#0	Ab0	25.96
21	A0		27.50
22	A#0	Bb0	29.14
23	B0		30.87
24	C1		32.70
25	C#1	Db1	34.65
26	D1		36.71
27	D#1	Eb1	38.89
28	E1		41.20
29	F1		43.65
30	F#1	Gb1	46.25
31	G1		49.00
32	G#1	Ab1	51.91
33	A1		55.00
34	A#1	Bb1	58.27
35	B1		61.74
36	C2		65.41
37	C#2	Db2	69.30
38	D2		73.42
39	D#2	Eb2	77.78
40	E2		82.41
41	F2		87.31
42	F#2	Gb2	92.50
43	G2		98.00
44	G#2	Ab2	103.83
45	A2		110.00
46	A#2	Bb2	116.54
47	B2		123.47
48	C3		130.81
49	C#3	Db3	138.59
50	D3		146.83
51	D#3	Eb3	155.56
52	E3		164.81
53	F3		174.61
54	F#3	Gb3	185.00
55	G3		196.00
56	G#3	Ab3	207.65
57	A3		220.00
58	A#3	Bb3	233.08
59	B3		246.94
60	C4		261.63
61	C#4	Db4	277.18
62	D4		293.66
63	D#4	Eb4	311.13
64	E4		329.63
65	F4		349.23
66	F#4	Gb4	369.99
67	G4		392.00
68	G#4	Ab4	415.30
69	A4		440.00
70	A#4	Bb4	466.16
71	B4		493.88
72	C5		523.25
73	C#5	Db5	554.37
74	D5		587.33
75	D#5	Eb5	622.25
76	E5		659.26
77	F5		698.46
78	F#5	Gb5	739.99
79	G5		783.99
80	G#5	Ab5	830.61
81	A5		880.00
82	A#5	Bb5	932.33
83	B5		987.77
84	C6		1046.50
85	C#6	Db6	1108.73
86	D6		1174.66
87	D#6	Eb6	1244.51
88	E6		1318.51
89	F6		1396.91
90	F#6	Gb6	1479.98
91	G6		1567.98
92	G#6	Ab6	1661.22
93	A6		1760.00
94	A#6	Bb6	1864.66
95	B6		1975.53
96	C7		2093.00
97	C#7	Db7	2217.46
98	D7		2349.32
99	D#7	Eb7	2489.02
100	E7		2637.02
101	F7		2793.83
102	F#7	Gb7	2959.96
103	G7		3135.96
104	G#7	Ab7	3322.44
105	A7		3520.00
106	A#7	Bb7	3729.31
107	B7		3951.07
108	C8		4186.01
109	C#8	Db8	4434.92
110	D8		4698.64
111	D#8	Eb8	4978.03
112	E8		5274.04
113	F8		5587.65
114	F#8	Gb8	5919.91
115	G8		6271.93
116	G#8	Ab8	6644.88
117	A8		7040.00
118	A#8	Bb8	7458.62
119	B8		7902.13
120	C9		8372.02
121	C#9	Db9	8869.84
122	D9		9397.27
123	D#9	Eb9	9956.06
124	E9		10548.08
125	F9		11175.30
126	F#9	Gb9	11839.82
127	G9		12543.85

How the math works

MIDI to frequency
freq = refA4 * 2 ^ ((midi - 69) / 12)
A4 is MIDI 69 by definition. Each semitone multiplies the frequency by the twelfth root of two (about 1.05946).
Frequency to MIDI
midi = 69 + 12 * log2(freq / refA4)
The result is rounded to the nearest integer MIDI note. The remainder, multiplied by 100, gives the cents offset from that note in 12-TET.
Cents and tuning drift
One cent is one hundredth of a semitone. A tuner usually starts showing a perceptible drift at about 5 cents. Cents are linear in log frequency, so +100 cents is exactly one semitone up at any starting pitch.
Tuning reference
A4 = 440 Hz is the ISO standard since 1955. Many orchestras prefer 442 or 444 for a brighter sound. Baroque ensembles often use 415, exactly one semitone below modern A4. Changing the reference scales every note proportionally.
Period and wavelength
The period is one divided by frequency, useful for setting up audio delay lines, LFO rates, and analog VCO calibration. The wavelength shown is in dry air at 20 degrees Celsius (speed of sound 343 m/s), useful for speaker and room layout.
MIDI note range
MIDI defines 128 notes, 0 (C-1) through 127 (G9). The 88-key piano covers MIDI 21 (A0) through MIDI 108 (C8). Synthesizers that respect the MIDI spec accept the full 0 to 127 range.

All math runs in your browser with double-precision floating point. Nothing you type here is uploaded.

How to use

Pick what you want to enter: Note name (like A4 or C#5), MIDI number (0 to 127), or Frequency (Hz).
Type the value. Sharps (#), flats (b), and Unicode accidentals are accepted; commas are converted to decimal points; the suffix 'Hz' is optional.
Adjust the A4 tuning reference if you are not using the 440 Hz standard. Presets cover 432, 441, 442, 444, and the baroque 415.
Read the result card for the note name (sharp and flat), MIDI number, frequency, period, and wavelength in air. Free-frequency inputs also show the cents offset from the nearest 12-TET note.
Click a piano key to load that note, or pick a row in the full MIDI table at the bottom. Copy buttons lift the note, the MIDI number, or the frequency for use elsewhere.

About this tool

Note Frequency Converter is a three-way bridge between musical note names, MIDI note numbers, and frequency in hertz, using 12-tone equal temperament (12-TET). Pick the input you have, type the value, and the other two are computed instantly with a configurable A4 tuning reference. Defaults to the international standard A4 = 440 Hz with one-tap presets for 432 Hz (the alternative new-age tuning), 441 and 442 Hz (common pro audio and modern orchestral references), 444 Hz (some American symphonies), and 415 Hz (historical baroque pitch). Frequencies that fall between two 12-TET notes are snapped to the nearest note and the cents offset is reported so guitar techs, vocal coaches, and audio engineers can read drift the same way a dedicated tuner does. The output card also surfaces the period in milliseconds (handy for synth LFOs and analog VCO calibration) and the wavelength in dry air at 20 degrees Celsius (handy for speaker placement and room layout). A full 88-key piano keyboard runs across the page so you can click any key from A0 (MIDI 21) through C8 (MIDI 108) to load it, and a scrollable MIDI table prints every one of the 128 MIDI notes (0 to 127) with the chosen tuning baked in, exportable as TSV with a single click. All math runs natively in JavaScript with double-precision floating point. Note names, MIDI numbers, frequencies, and the tuning reference you choose never leave your browser.

Free to use. Works in your browser. No signup, no login.

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