Why is A4 = 440 Hz the standard reference pitch?

A4 = 440 Hz was standardised by ISO 16 in 1975 and adopted by most orchestras, instrument manufacturers, and tuning devices worldwide. Before standardisation, concert A ranged from 415 Hz to 466 Hz depending on country and era. Some orchestras and early music ensembles still use A = 415 Hz (Baroque pitch) or A = 432 Hz (promoted in some alternative tuning communities, though not supported by scientific evidence).

How is the frequency of each note calculated?

Every semitone up or down multiplies or divides the frequency by the 12th root of 2 (≈1.05946). Starting from A4 = 440 Hz: A#4 = 440 × 2^(1/12) ≈ 466.16 Hz; G4 = 440 × 2^(-2/12) ≈ 392 Hz. Each octave exactly doubles the frequency — A5 = 880 Hz, A3 = 220 Hz. This equal temperament system divides the octave into 12 equal semitones.

What is a MIDI note number and how does it relate to note names?

MIDI note numbers are integers from 0 to 127 used by electronic instruments and DAWs to represent pitches. Middle C (C4) is MIDI note 60 in most DAWs. A4 (440 Hz) is MIDI note 69. Each semitone is one MIDI number apart. Note names use the convention: C4 = middle C, with each octave starting at C. Some DAWs use C3 = middle C (MIDI 60) — always check your DAW's convention.

Note Frequency Table — Equal Temperament

Frequencies for every note across the MIDI range, with an adjustable A4 reference.

Note	MIDI	Frequency (Hz)	Wavelength (m)	Period (ms)
C_-1	0	8.1758	41.953	122.312
C#_-1	1	8.6620	39.598	115.447
D_-1	2	9.1770	37.376	108.968
D#_-1	3	9.7227	35.278	102.852
E_-1	4	10.30	33.298	97.079
F_-1	5	10.91	31.429	91.631
F#_-1	6	11.56	29.665	86.488
G_-1	7	12.25	28.000	81.634
G#_-1	8	12.98	26.429	77.052
A_-1	9	13.75	24.945	72.727
A#_-1	10	14.57	23.545	68.645
B_-1	11	15.43	22.224	64.793
C₀	12	16.35	20.977	61.156
C#₀	13	17.32	19.799	57.724
D₀	14	18.35	18.688	54.484
D#₀	15	19.45	17.639	51.426
E₀	16	20.60	16.649	48.540
F₀	17	21.83	15.715	45.815
F#₀	18	23.12	14.833	43.244
G₀	19	24.50	14.000	40.817
G#₀	20	25.96	13.214	38.526
A₀	21	27.50	12.473	36.364
A#₀	22	29.14	11.773	34.323
B₀	23	30.87	11.112	32.396
C₁	24	32.70	10.488	30.578
C#₁	25	34.65	9.900	28.862
D₁	26	36.71	9.344	27.242
D#₁	27	38.89	8.820	25.713
E₁	28	41.20	8.325	24.270
F₁	29	43.65	7.857	22.908
F#₁	30	46.25	7.416	21.622
G₁	31	49.00	7.000	20.408
G#₁	32	51.91	6.607	19.263
A₁	33	55.00	6.236	18.182
A#₁	34	58.27	5.886	17.161
B₁	35	61.74	5.556	16.198
C₂	36	65.41	5.244	15.289
C#₂	37	69.30	4.950	14.431
D₂	38	73.42	4.672	13.621
D#₂	39	77.78	4.410	12.856
E₂	40	82.41	4.162	12.135
F₂	41	87.31	3.929	11.454
F#₂	42	92.50	3.708	10.811
G₂	43	98.00	3.500	10.204
G#₂	44	103.83	3.304	9.631
A₂	45	110.00	3.118	9.091
A#₂	46	116.54	2.943	8.581
B₂	47	123.47	2.778	8.099
C₃	48	130.81	2.622	7.645
C#₃	49	138.59	2.475	7.215
D₃	50	146.83	2.336	6.810
D#₃	51	155.56	2.205	6.428
E₃	52	164.81	2.081	6.067
F₃	53	174.61	1.964	5.727
F#₃	54	185.00	1.854	5.405
G₃	55	196.00	1.750	5.102
G#₃	56	207.65	1.652	4.816
A₃	57	220.00	1.559	4.545
A#₃	58	233.08	1.472	4.290
B₃	59	246.94	1.389	4.050
C₄	60	261.63	1.311	3.822
C#₄	61	277.18	1.237	3.608
D₄	62	293.66	1.168	3.405
D#₄	63	311.13	1.102	3.214
E₄	64	329.63	1.041	3.034
F₄	65	349.23	0.982	2.863
F#₄	66	369.99	0.927	2.703
G₄	67	392.00	0.875	2.551
G#₄	68	415.30	0.826	2.408
A₄ A440	69	440.00	0.780	2.273
A#₄	70	466.16	0.736	2.145
B₄	71	493.88	0.694	2.025
C₅	72	523.25	0.656	1.911
C#₅	73	554.37	0.619	1.804
D₅	74	587.33	0.584	1.703
D#₅	75	622.25	0.551	1.607
E₅	76	659.26	0.520	1.517
F₅	77	698.46	0.491	1.432
F#₅	78	739.99	0.464	1.351
G₅	79	783.99	0.438	1.276
G#₅	80	830.61	0.413	1.204
A₅	81	880.00	0.390	1.136
A#₅	82	932.33	0.368	1.073
B₅	83	987.77	0.347	1.012
C₆	84	1046.5	0.328	0.956
C#₆	85	1108.7	0.309	0.902
D₆	86	1174.7	0.292	0.851
D#₆	87	1244.5	0.276	0.804
E₆	88	1318.5	0.260	0.758
F₆	89	1396.9	0.246	0.716
F#₆	90	1480.0	0.232	0.676
G₆	91	1568.0	0.219	0.638
G#₆	92	1661.2	0.206	0.602
A₆	93	1760.0	0.195	0.568
A#₆	94	1864.7	0.184	0.536
B₆	95	1975.5	0.174	0.506
C₇	96	2093.0	0.164	0.478
C#₇	97	2217.5	0.155	0.451
D₇	98	2349.3	0.146	0.426
D#₇	99	2489.0	0.138	0.402
E₇	100	2637.0	0.130	0.379
F₇	101	2793.8	0.123	0.358
F#₇	102	2960.0	0.116	0.338
G₇	103	3136.0	0.109	0.319
G#₇	104	3322.4	0.103	0.301
A₇	105	3520.0	0.097	0.284
A#₇	106	3729.3	0.092	0.268
B₇	107	3951.1	0.087	0.253
C₈	108	4186.0	0.082	0.239
C#₈	109	4434.9	0.077	0.225
D₈	110	4698.6	0.073	0.213
D#₈	111	4978.0	0.069	0.201
E₈	112	5274.0	0.065	0.190
F₈	113	5587.7	0.061	0.179
F#₈	114	5919.9	0.058	0.169
G₈	115	6271.9	0.055	0.159
G#₈	116	6644.9	0.052	0.150
A₈	117	7040.0	0.049	0.142
A#₈	118	7458.6	0.046	0.134
B₈	119	7902.1	0.043	0.127
C₉	120	8372.0	0.041	0.119
C#₉	121	8869.8	0.039	0.113
D₉	122	9397.3	0.036	0.106
D#₉	123	9956.1	0.034	0.100
E₉	124	10548.1	0.033	0.095
F₉	125	11175.3	0.031	0.089
F#₉	126	11839.8	0.029	0.084
G₉	127	12543.9	0.027	0.080

128 of 128 notes · A4 = 440 Hz · Speed of sound = 343 m/s

How note frequencies are calculated

Equal temperament divides the octave into twelve equal ratios, so every semitone is the same multiplicative step.

f = A4 × 2^((n − 69) / 12)

f: Frequency of the note in hertz
A4: Reference pitch, conventionally 440 Hz
n: MIDI note number — A4 is 69, middle C (C4) is 60
2^(1/12): The semitone ratio, approximately 1.059463

Worked example

Note: C5 (MIDI 72)
Calculation: 440 × 2^((72 − 69) / 12)
Exponent: 3/12 = 0.25

523.25 Hz

Octaves are exact doublings: A3 is 220 Hz, A4 is 440, A5 is 880. Every other interval is irrational — which is exactly the compromise equal temperament makes.

Why A = 440 Hz, and when it is not

A4 = 440 Hz was standardised by ISO in 1955 and reaffirmed in 1975. Before that, concert pitch varied widely: Baroque ensembles commonly worked around 415 Hz (roughly a semitone flat), and nineteenth-century orchestras drifted steadily upward as higher tuning was perceived as brighter — a trend that only stopped because it was straining singers and instruments.

Deviations you will still meet:

A = 442 or 443 Hz. Many European orchestras tune slightly sharp of 440 for a brighter sound. Vienna and Berlin have historically used 443.
A = 415 Hz. Baroque performance practice, a semitone below modern pitch.
A = 432 Hz. Promoted with various claims about natural resonance and wellbeing. There is no scientific support for any of them, and the historical arguments do not hold up either — but it is harmless, and if you are playing solo it makes no difference to anything except which recordings you can play along with.

What matters in practice is that everyone playing together uses the same reference. The absolute value is convention.

About

The Note Frequencies table lists all 128 MIDI notes (C−1 to G9) with their exact frequency in Hz calculated relative to the A4 = 440 Hz standard pitch. It also shows the MIDI note number (0–127), the wavelength in metres at the speed of sound (343 m/s), and the period in milliseconds. Filter by octave or search by note name, frequency, or MIDI number.

How to use

1 Browse all 128 MIDI notes in the table.
2 Filter by octave using the Oct 0–Oct 8 buttons.
3 Search by note name (e.g. "A4"), frequency (e.g. "440"), or MIDI number.
4 A4 (440 Hz) is highlighted as the universal reference pitch.

Why is A4 = 440 Hz the standard reference pitch?: A4 = 440 Hz was standardised by ISO 16 in 1975 and adopted by most orchestras, instrument manufacturers, and tuning devices worldwide. Before standardisation, concert A ranged from 415 Hz to 466 Hz depending on country and era. Some orchestras and early music ensembles still use A = 415 Hz (Baroque pitch) or A = 432 Hz (promoted in some alternative tuning communities, though not supported by scientific evidence).
How is the frequency of each note calculated?: Every semitone up or down multiplies or divides the frequency by the 12th root of 2 (≈1.05946). Starting from A4 = 440 Hz: A#4 = 440 × 2^(1/12) ≈ 466.16 Hz; G4 = 440 × 2^(-2/12) ≈ 392 Hz. Each octave exactly doubles the frequency — A5 = 880 Hz, A3 = 220 Hz. This equal temperament system divides the octave into 12 equal semitones.
What is a MIDI note number and how does it relate to note names?: MIDI note numbers are integers from 0 to 127 used by electronic instruments and DAWs to represent pitches. Middle C (C4) is MIDI note 60 in most DAWs. A4 (440 Hz) is MIDI note 69. Each semitone is one MIDI number apart. Note names use the convention: C4 = middle C, with each octave starting at C. Some DAWs use C3 = middle C (MIDI 60) — always check your DAW's convention.

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