📻 Note Frequency Calculator
Select a musical note and octave to calculate its frequency in Hz, based on standard A4 = 440 Hz equal temperament tuning.
Equal temperament, counted from A4
The note and octave first become a MIDI number, and the frequency is then a fixed number of semitone steps away from the 440 Hz reference:
m = (octave + 1) × 12 + note index C = 0, C# = 1 ... B = 11
f = 440 × 2^((m - 69) / 12) Hz
one semitone = × 2^(1/12) = 1.059463 one octave = × 2A4 is index 9 in octave 4, so m = 69 and the exponent is zero: 440.00 Hz exactly. Middle C, C4, is nine semitones below at m = 60, giving 440 × 2^(-9/12) = 261.63 Hz. Every semitone up multiplies by 1.0595, which is about 5.95 percent, and twelve of those multiply out to exactly 2.
Landmarks and what the tool assumes
| Note | MIDI | Frequency |
|---|---|---|
| C2 | 36 | 65.41 Hz |
| E2 (guitar low E) | 40 | 82.41 Hz |
| C4 (middle C) | 60 | 261.63 Hz |
| A4 (tuning A) | 69 | 440.00 Hz |
| C6 | 84 | 1046.50 Hz |
- Octaves run 2 to 6 only, so C2 to B6, or 65.41 Hz to 1975.53 Hz. For anything below, halve the octave-2 figure once per octave.
- Middle C is C4 here and MIDI 60. Some hardware labels the same note C3 - the pitch is identical, only the octave label differs.
Frequently asked questions
What is the frequency of middle C?
261.63 Hz, written C4 and numbered 60 in MIDI. It is nine semitones below the 440 Hz A, so 440 divided by 2^(9/12).
How do I calculate the frequency of any note?
Count the semitones from A4 and put that number in 440 × 2^(n/12), using a negative n for notes below it. G3 is fourteen semitones down: 440 / 2.2449 = 196.00 Hz.
Why is A4 440 Hz and not 432?
440 Hz has been the international standard since 1955, and every tuner and keyboard ships set to it. 432 Hz is a modern preference with no acoustic advantage; if you want it, multiply these figures by 0.98182.