Free online tool

Note Frequency Calculator: Hz, MIDI and Piano Key Numbers

Convert note names to Hz, MIDI and piano key numbers (A4 adjustable), find the nearest note and cents for any frequency, and print all 88 key frequencies.

Reference pitch A4

Note

Frequency (Hz)

MIDI number

Piano key (A0 = 1 … C8 = 88)

Cents offset

A4 = 440.00 Hz · MIDI 69 · key 49 · wavelength 0.780 m

Type in any box and the others follow. Entering a frequency finds the nearest note and how many cents sharp or flat it is.

Piano key frequencies: all 88 keys

Equal temperament, A4 = 440 Hz. Wavelength is for sound in air at 20 °C (343 m/s).

Key	Note	MIDI	Frequency (Hz)	Wavelength (m)
1	A0	21	27.50	12.5
2	A#0 / Bb0	22	29.14	11.8
3	B0	23	30.87	11.1
4	C1	24	32.70	10.5
5	C#1 / Db1	25	34.65	9.90
6	D1	26	36.71	9.34
7	D#1 / Eb1	27	38.89	8.82
8	E1	28	41.20	8.32
9	F1	29	43.65	7.86
10	F#1 / Gb1	30	46.25	7.42
11	G1	31	49.00	7.00
12	G#1 / Ab1	32	51.91	6.61
13	A1	33	55.00	6.24
14	A#1 / Bb1	34	58.27	5.89
15	B1	35	61.74	5.56
16	C2	36	65.41	5.24
17	C#2 / Db2	37	69.30	4.95
18	D2	38	73.42	4.67
19	D#2 / Eb2	39	77.78	4.41
20	E2	40	82.41	4.16
21	F2	41	87.31	3.93
22	F#2 / Gb2	42	92.50	3.71
23	G2	43	98.00	3.50
24	G#2 / Ab2	44	103.83	3.30
25	A2	45	110.00	3.12
26	A#2 / Bb2	46	116.54	2.94
27	B2	47	123.47	2.78
28	C3	48	130.81	2.62
29	C#3 / Db3	49	138.59	2.47
30	D3	50	146.83	2.34
31	D#3 / Eb3	51	155.56	2.20
32	E3	52	164.81	2.08
33	F3	53	174.61	1.96
34	F#3 / Gb3	54	185.00	1.85
35	G3	55	196.00	1.75
36	G#3 / Ab3	56	207.65	1.65
37	A3	57	220.00	1.56
38	A#3 / Bb3	58	233.08	1.47
39	B3	59	246.94	1.39
40	C4	60	261.63	1.31
41	C#4 / Db4	61	277.18	1.24
42	D4	62	293.66	1.17
43	D#4 / Eb4	63	311.13	1.10
44	E4	64	329.63	1.04
45	F4	65	349.23	0.982
46	F#4 / Gb4	66	369.99	0.927
47	G4	67	392.00	0.875
48	G#4 / Ab4	68	415.30	0.826
49	A4	69	440.00	0.780
50	A#4 / Bb4	70	466.16	0.736
51	B4	71	493.88	0.694
52	C5	72	523.25	0.656
53	C#5 / Db5	73	554.37	0.619
54	D5	74	587.33	0.584
55	D#5 / Eb5	75	622.25	0.551
56	E5	76	659.26	0.520
57	F5	77	698.46	0.491
58	F#5 / Gb5	78	739.99	0.464
59	G5	79	783.99	0.438
60	G#5 / Ab5	80	830.61	0.413
61	A5	81	880.00	0.390
62	A#5 / Bb5	82	932.33	0.368
63	B5	83	987.77	0.347
64	C6	84	1046.50	0.328
65	C#6 / Db6	85	1108.73	0.309
66	D6	86	1174.66	0.292
67	D#6 / Eb6	87	1244.51	0.276
68	E6	88	1318.51	0.260
69	F6	89	1396.91	0.246
70	F#6 / Gb6	90	1479.98	0.232
71	G6	91	1567.98	0.219
72	G#6 / Ab6	92	1661.22	0.206
73	A6	93	1760.00	0.195
74	A#6 / Bb6	94	1864.66	0.184
75	B6	95	1975.53	0.174
76	C7	96	2093.00	0.164
77	C#7 / Db7	97	2217.46	0.155
78	D7	98	2349.32	0.146
79	D#7 / Eb7	99	2489.02	0.138
80	E7	100	2637.02	0.130
81	F7	101	2793.83	0.123
82	F#7 / Gb7	102	2959.96	0.116
83	G7	103	3135.96	0.109
84	G#7 / Ab7	104	3322.44	0.103
85	A7	105	3520.00	0.0974
86	A#7 / Bb7	106	3729.31	0.0920
87	B7	107	3951.07	0.0868
88	C8	108	4186.01	0.0819

About the Note Frequency Calculator

The Note Frequency Calculator converts a note name, such as Bb3 or C#5, into its frequency in hertz (Hz). It also works in reverse: enter a frequency and it finds the nearest note and how many cents away it is. For each note it shows the MIDI number and the piano key number. It runs free in your web browser, with no sign-up.

You can set the reference pitch for A4 to 440 Hz, the modern standard known as A440, or choose another tuning from the menu, such as 432 Hz. The tool also prints a note frequency chart covering all 88 piano keys.

Whether you are checking an A440 piano tuning, learning how piano keys map to pitch, or comparing tuning standards, the same controls apply.

How to use the Note Frequency Calculator

Choose the reference pitch for A4. Pick 440 Hz (standard) for the modern A440 tuning, pick another option such as 432 Hz or 415 Hz (Baroque), or choose Custom… and enter a value in Custom A4 in Hz.
Type a note such as Bb3 or C#5 into the Note box. The Frequency (Hz), MIDI number and Piano key (A0 = 1 … C8 = 88) boxes update at once. You can also start from any of those three boxes, and the others will follow.
For a frequency that falls between two notes, read the nearest note and the Cents offset. To detune a note on purpose, type a value into Cents offset.
Press ▶ Hear it to play the pitch, or press Print table to print the 88-key frequency chart.

The printed table lists each key with its Key, MIDI and Wavelength (m) values alongside its frequency. You can keep a copy of the table without entering each note again.

The most useful tip is to set the Reference pitch A4 before you read any values, because every frequency depends on it. Two other habits help: read the cents value for in-between frequencies, and try different spellings of the same note.

Spellings do not change the result. B#3, C4 and D𝄫4 all give 261.63 Hz at A4 = 440 Hz, so use whichever name matches your music.

A cents value shows how far a pitch sits from the note. +12 means 12 hundredths of a semitone above the note shown.

How do you convert a note to a frequency?#

Modern pianos are tuned in 12-tone equal temperament. The octave is split into 12 equal steps, so each semitone multiplies the frequency by the twelfth root of 2, about 1.059463. Going up one octave (12 semitones) doubles the frequency, and going down halves it. With A4 at 440 Hz, A3 is therefore 220 Hz and A5 is 880 Hz.

Scientific pitch notation writes a letter followed by an octave number. The octave number changes at C, not at A, so middle C is C4 and the A above it is A4. The calculator uses MIDI numbers, where C4 is 60 and A4 is 69. For any note, MIDI = 12 × (octave + 1) + semitones above C. A piano key number is the MIDI number minus 20, so A0 is key 1, A4 is key 49 and C8 is key 88.

The frequency of the note with MIDI number n is f = 440 × 2^((n − 69) / 12). The same formula with a different reference pitch gives the other tunings in the menu: replace 440 with 432, 442 and so on. Enharmonic spellings share a pitch in equal temperament. C♯4 and D♭4 are the same key, and B♯3 is the same pitch as C4.

To go the other way, a frequency f gives a fractional MIDI number of 69 + 12 × log₂(f / 440). Round that to get the nearest note. The remainder, multiplied by 100, is the offset in cents. A cent is one hundredth of an equal-tempered semitone, so there are 1200 cents in an octave. The distance in cents between two frequencies f₁ and f₂ is 1200 × log₂(f₂ / f₁). A reading of +12 cents means the pitch is 12 hundredths of a semitone above the note shown. This is the calculation a chromatic tuner performs.

What are A440 and 432 Hz tuning?#

A440 and 432 Hz are two choices for the frequency of A4, the A above middle C. A440 sets A4 to 440 Hz, the modern standard. 432 Hz sets it to 432 Hz, a little lower, so every other note shifts down with it.

Each note’s frequency is calculated from A4 with the same formula, with 432 replacing 440. Going up one octave doubles the frequency, so with 432 Hz, A3 is 216 Hz and A5 is 864 Hz.

In the calculator, choose 440 Hz (standard) or 432 Hz under Reference pitch A4, or enter your own value with Custom….

Frequently asked questions

What is the frequency of middle C?

Middle C is C4, MIDI 60 and piano key 40. With A4 set to 440 Hz, it has a frequency of 261.63 Hz. Enharmonic spellings such as B♯3 give the same value.

What are the lowest and highest piano key frequencies?

The lowest key, A0, is 27.50 Hz, and the highest, C8, is 4186.01 Hz, both with A4 at 440 Hz. Those 88 keys span just over seven and a quarter octaves.

Why are the table values rounded to two decimals?

Equal-tempered frequencies are powers of 2^(1/12), so their decimal digits never end. Two decimals are finer than any ear or tuner can tell apart.

How is the wavelength of a note worked out?

The wavelength in air is λ = v / f, where v is 343 m/s, the speed of sound at about 20 °C. The speed of sound changes with temperature, so the values shift slightly in a warm or cold room. A0 has a wavelength of about 12.5 m, and C8 about 8 cm.

Is B#3 the same frequency as C4?

Yes. In equal temperament, B♯3, C4 and D𝄫4 are the same pitch, 261.63 Hz at A4 = 440 Hz. The calculator accepts any of these spellings in the Note box.

Is it free and does it need an account?

Yes. The Note Frequency Calculator is free, and you do not need to sign up or create an account. Nothing you enter is uploaded, because the tool runs in your browser.

Can I use it on a phone?

Yes. Because the tool runs in the web browser, any phone with a browser can open it, and there is nothing to install. Open the page as you would any website. If a control is hard to reach on a small screen, try turning your phone sideways.