How are note frequencies calculated?

Equal temperament uses the formula f = 440 × 2^((n − 69) / 12), where n is the MIDI note number and 69 is A4. Each semitone multiplies the frequency by the twelfth root of two, roughly 1.0595, so twelve semitones double the pitch exactly one octave higher.

A4 is the A above middle C, the standard concert-pitch reference adopted by ISO 16. Fixing it at 440 Hz defines the frequency of every other note in equal temperament. Some orchestras tune to 442 or 443 Hz, and 432 Hz is a popular alternative tuning.

What is a MIDI note number?

MIDI numbers map each piano key to an integer: middle C (C4) is 60 and A4 is 69. They give a compact, octave-aware way to identify pitches in software and hardware, and they feed directly into the frequency formula.

Why is middle C4 not exactly 256 Hz?

256 Hz for middle C comes from a scientific-pitch convention where each C is a power of two. Standard concert tuning anchors A4 at 440 Hz instead, which makes C4 about 261.63 Hz. The two systems simply use different reference points.

Does this work for 432 Hz tuning?

Yes. Change the A4 reference pitch to 432 and every note rescales by the ratio 432/440. The relative intervals stay identical because equal temperament is defined by ratios, not absolute frequencies.

Musical Note Frequency Reference

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Every note, every octave, in hertz

This reference lists the equal-temperament frequency of every musical note from C0 up to B8. It is built for musicians, audio developers, instrument builders and anyone wiring up a synthesiser or tuner. Frequencies are computed live from the A4 reference pitch you choose, so you can read off standard 440 Hz tuning or any alternative such as 432 Hz or 442 Hz.

How it works

In twelve-tone equal temperament, every semitone is the same frequency ratio: the twelfth root of two. Starting from a fixed anchor, the frequency of any note is:

f = A4 * 2 ^ ((n - 69) / 12)

Here n is the MIDI note number (A4 = 69) and A4 is the reference pitch in hertz. Because the exponent is linear in n, moving up twelve semitones adds 12/12 = 1 to the exponent and doubles the frequency — one octave. Moving down twelve halves it. That single formula generates the entire table.

Tips and examples

A4 = 440 Hz gives A5 = 880 Hz, A3 = 220 Hz and middle C (C4) about 261.63 Hz.
Each semitone differs by roughly 5.95 percent; that is why adjacent notes look close but never repeat until the octave.
To match a violin tuned to 442 Hz, set the reference to 442 and the whole table shifts up by the ratio 442/440.
MIDI 60 is middle C; searching 60 jumps straight to it.