Note frequency calculator

Type how many semitones sit between the note and A4. Zero is concert 440 Hz. Plus 12 is A5 = 880 Hz, minus 12 is A3 = 220 Hz. Minus 9 is C4, about 261.63 Hz. Plus 3 is C5, 523.25 Hz.

Interval from two Hz values: semitones between frequencies. A shift: transpose in Hz. Wave: sound wavelength.

Result

Enter a value. The result shows up here.

How it works

Equal temperament splits the octave into twelve even semitones. Each semitone multiplies frequency by the twelfth root of 2, about 1.05946. We start from A4 = 440 Hz, not 432. The formula is f = 440 × 2^(k/12). Typed 0 is A4 and returns 440.00 Hz.

Plus 12 is A5 = 880.00 Hz. Minus 12 is A3 = 220.00 Hz. Plus 3, three semitones above A, is C5 ≈ 523.25 Hz. Minus 9 is C4 ≈ 261.63 Hz. Plus 7 is E5 ≈ 659.26 Hz, a tempered fifth, not just 660. Plus 2 is 493.88 Hz. Minus 5 is E4 ≈ 329.63 Hz.

Negative k is allowed and means notes below A4. MIDI 69 is A4, so k = n − 69. MIDI 60 (C4) is −9, MIDI 72 (C5) is +3. There is no octave cap in the code, but extreme k quickly leaves the hearing range. The result has two decimal places in hertz.

Note hertz from A4 = 440 Hz in 12-TET. If the base should be something other than 440, open transposition and type your own f1. If you already have two frequencies, the interval page gives you k, not hertz from concert pitch.

Type k, click Calculate. A comma in 0.5 (fifty cents above A4) works. Wavelength from those hertz is on the neighbouring page: 440 Hz at 343 m/s is 0.7795 m.

On a score you count semitones from A first, then hertz. A tuner that only shows cents does not replace this formula: convert the cents separately and add them to k as a fraction.

How to use

Type the semitone offset from A4. Zero is A4 = 440 Hz. Negatives go down.
For C4 type −9, for C5 type 3, for A5 type 12. A 432 Hz concert pitch is not in this formula.
Click Calculate. 0 gives 440.00 Hz, 12 gives 880.00 Hz, −12 gives 220.00 Hz.
When the base is not 440, open transposition and type your own f1 plus the same k.
For a wave from these hertz, open sound wavelength. For k from two Hz values, open the interval page.

Formula

f = 440 × 2^k/12

k = semitones from A4. A4 = 440 Hz, equal temperament. Negative k is allowed. An empty field is not zero until you type something.

Note Hz from A4 = 440

Here f = 440 × 2^(k/12). Zero semitones is 440 Hz. Plus 12 is A5 = 880 Hz, minus 12 is A3 = 220 Hz. Minus 9 is C4, about 261.63 Hz.

Hz: Hertz of the result, cycles per second. A4 in this calculator is 440. k = 3 gives C5 = 523.25 Hz. Empty k is not a concert-pitch zero.
A4: Concert pitch, the 440 Hz base at k = 0. Every other note is 2^(k/12) from that four hundred forty, in equal temperament.

Real-life examples

Example 1

0 semitones -> 440.00 Hz, concert A.

Example 2

+12 -> 880.00 Hz above A4.

Example 3

-12 -> 220.00 Hz below A4.

Example 4

+3 -> 523.25 Hz, C above A4.

Example 5

-9 semitones -> 261.63 Hz, C4.

Example 6

+7 -> 659.26 Hz, a fifth from A4.

Example 7

+2 -> 493.88 Hz, two semitones up.

Example 8

-5 -> 329.63 Hz, E below A4.

Ways to use this calculator

You check how many Hz a MIDI note has after counting semitones from A4, before you set an oscillator.
You compare concert 440 with a scored note when the tuner only shows a cents offset.
You take k = 7 and confirm 659.26 Hz before someone hands you just 660 as a “pure fifth”.

Frequently asked questions

How many Hz are A4, A5, and A3?

440.00 Hz, 880.00 Hz, and 220.00 Hz. Zero, plus 12, and minus 12 semitones from A4.

What k do I type for C4 and C5?

C4 is −9, about 261.63 Hz. C5 is +3, about 523.25 Hz.

How many Hz is a fifth from A4?

659.26 Hz at k = 7. Just 3:2 would be 660 Hz. This page is 12-TET.

What do I get at k = 2 and k = −5?

493.88 Hz and 329.63 Hz. The second is E4, five semitones below A4.

Is typed 0 really 440 Hz?

Yes. 440 × 2^0 = 440. That is concert pitch, not missing data.

How do I turn a MIDI number into k?

Subtract 69. MIDI 69 is A4. MIDI 60 is C4 and k = −9. MIDI 72 is C5 and k = 3.

Can I compute from 432 Hz?

Not in this calculator. The base is 440. For 432, open transposition and type f1 = 432.

Can k be a fraction?

Yes. 0.5 is fifty cents above A4, about 452.89 Hz.

Where do I take wavelength from these hertz?

On the sound-wavelength page. 440 Hz and 343 m/s give 0.7795 m.

How is this different from transposition?

Here the base is always 440. There you type your own f1 and the same k.

Knowledge sources

Frequency and intervals in this calculator follow the hertz and A440 concert pitch.

Page updated in 2026.