How are note frequencies calculated?

In twelve-tone equal temperament each semitone multiplies the frequency by the twelfth root of two (about 1.0595). From A4 at 440 Hz, a note n semitones away is 440 × 2^(n/12): an octave up doubles it to 880 Hz, an octave down halves it to 220 Hz.

What is the frequency of middle C?

Middle C (C4, MIDI note 60) is 261.63 Hz when A4 is 440 Hz. Some software calls it C3; the pitch is the same, only the octave label differs.

What's the difference between 432 Hz and 440 Hz tuning?

Only the reference: 432 Hz tuning puts every note about 32 cents (a third of a semitone) lower. ISO 16 sets A4 at 440 Hz, and most recorded music uses it; some orchestras tune to 442 or 443 for a brighter sound.

What does the MIDI number mean?

MIDI numbers every semitone from 0 to 127; A4 is 69 and middle C is 60. It's how DAWs and controllers name a pitch, so it is handy when programming notes or reading MIDI files.

The length of one cycle in air (speed of sound 343 m/s at 20 °C) tells you which room dimensions reinforce a note. Low notes have wavelengths of several metres, which is why bass builds up in small rooms.

Free tool

Every note, in hertz. C0 to B8, at 440 Hz or any tuning. Click to hear one.

A4 reference (Hz)

Note frequencies with A4 = 440 Hz
Note	Octave	MIDI	Frequency (Hz)	Wavelength
	0	12	16.35	20.98 m
	0	13	17.32	19.80 m
	0	14	18.35	18.69 m
	0	15	19.45	17.64 m
	0	16	20.60	16.65 m
	0	17	21.83	15.71 m
	0	18	23.12	14.83 m
	0	19	24.50	14.00 m
	0	20	25.96	13.21 m
	0	21	27.50	12.47 m
	0	22	29.14	11.77 m
	0	23	30.87	11.11 m
	1	24	32.70	10.49 m
	1	25	34.65	9.90 m
	1	26	36.71	9.34 m
	1	27	38.89	8.82 m
	1	28	41.20	8.32 m
	1	29	43.65	7.86 m
	1	30	46.25	7.42 m
	1	31	49.00	7.00 m
	1	32	51.91	6.61 m
	1	33	55.00	6.24 m
	1	34	58.27	5.89 m
	1	35	61.74	5.56 m
	2	36	65.41	5.24 m
	2	37	69.30	4.95 m
	2	38	73.42	4.67 m
	2	39	77.78	4.41 m
	2	40	82.41	4.16 m
	2	41	87.31	3.93 m
	2	42	92.50	3.71 m
	2	43	98.00	3.50 m
	2	44	103.83	3.30 m
	2	45	110.00	3.12 m
	2	46	116.54	2.94 m
	2	47	123.47	2.78 m
	3	48	130.81	2.62 m
	3	49	138.59	2.47 m
	3	50	146.83	2.34 m
	3	51	155.56	2.20 m
	3	52	164.81	2.08 m
	3	53	174.61	1.96 m
	3	54	185.00	1.85 m
	3	55	196.00	1.75 m
	3	56	207.65	1.65 m
	3	57	220.00	1.56 m
	3	58	233.08	1.47 m
	3	59	246.94	1.39 m
middle C	4	60	261.63	1.31 m
	4	61	277.18	1.24 m
	4	62	293.66	1.17 m
	4	63	311.13	1.10 m
	4	64	329.63	1.04 m
	4	65	349.23	98.2 cm
	4	66	369.99	92.7 cm
	4	67	392.00	87.5 cm
	4	68	415.30	82.6 cm
	4	69	440.00	78.0 cm
	4	70	466.16	73.6 cm
	4	71	493.88	69.4 cm
	5	72	523.25	65.6 cm
	5	73	554.37	61.9 cm
	5	74	587.33	58.4 cm
	5	75	622.25	55.1 cm
	5	76	659.26	52.0 cm
	5	77	698.46	49.1 cm
	5	78	739.99	46.4 cm
	5	79	783.99	43.8 cm
	5	80	830.61	41.3 cm
	5	81	880.00	39.0 cm
	5	82	932.33	36.8 cm
	5	83	987.77	34.7 cm
	6	84	1046.50	32.8 cm
	6	85	1108.73	30.9 cm
	6	86	1174.66	29.2 cm
	6	87	1244.51	27.6 cm
	6	88	1318.51	26.0 cm
	6	89	1396.91	24.6 cm
	6	90	1479.98	23.2 cm
	6	91	1567.98	21.9 cm
	6	92	1661.22	20.6 cm
	6	93	1760.00	19.5 cm
	6	94	1864.66	18.4 cm
	6	95	1975.53	17.4 cm
	7	96	2093.00	16.4 cm
	7	97	2217.46	15.5 cm
	7	98	2349.32	14.6 cm
	7	99	2489.02	13.8 cm
	7	100	2637.02	13.0 cm
	7	101	2793.83	12.3 cm
	7	102	2959.96	11.6 cm
	7	103	3135.96	10.9 cm
	7	104	3322.44	10.3 cm
	7	105	3520.00	9.7 cm
	7	106	3729.31	9.2 cm
	7	107	3951.07	8.7 cm
	8	108	4186.01	8.2 cm
	8	109	4434.92	7.7 cm
	8	110	4698.64	7.3 cm
	8	111	4978.03	6.9 cm
	8	112	5274.04	6.5 cm
	8	113	5587.65	6.1 cm
	8	114	5919.91	5.8 cm
	8	115	6271.93	5.5 cm
	8	116	6644.88	5.2 cm
	8	117	7040.00	4.9 cm
	8	118	7458.62	4.6 cm
	8	119	7902.13	4.3 cm

How it works

01

Pick a reference

A4 = 440 Hz is the standard. Choose 432 or 442, or type any value from 400 to 480, and every frequency updates.

02

Find the note

Each row gives the note (with its flat name for black keys), octave, MIDI number, frequency and wavelength in air.

03

Listen

Click a row to hear a pure sine tone at that pitch, generated in your browser.

Questions

How are note frequencies calculated?: In twelve-tone equal temperament each semitone multiplies the frequency by the twelfth root of two (about 1.0595). From A4 at 440 Hz, a note n semitones away is 440 × 2^(n/12): an octave up doubles it to 880 Hz, an octave down halves it to 220 Hz.
What is the frequency of middle C?: Middle C (C4, MIDI note 60) is 261.63 Hz when A4 is 440 Hz. Some software calls it C3; the pitch is the same, only the octave label differs.
What's the difference between 432 Hz and 440 Hz tuning?: Only the reference: 432 Hz tuning puts every note about 32 cents (a third of a semitone) lower. ISO 16 sets A4 at 440 Hz, and most recorded music uses it; some orchestras tune to 442 or 443 for a brighter sound.
What does the MIDI number mean?: MIDI numbers every semitone from 0 to 127; A4 is 69 and middle C is 60. It's how DAWs and controllers name a pitch, so it is handy when programming notes or reading MIDI files.
Why show wavelength?: The length of one cycle in air (speed of sound 343 m/s at 20 °C) tells you which room dimensions reinforce a note. Low notes have wavelengths of several metres, which is why bass builds up in small rooms.

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