In twelve-tone equal temperament, each semitone multiplies frequency by the twelfth root of two.
How to use the Note Frequency Calculator
- MIDI note number — Middle C (C4) = 60, A4 = 69.
- Reference pitch A4
Results update as you type, and every field accepts the units shown in its menu.
How it works
The MIDI number of A4 is 69; each step up or down is one semitone.
Inputs explained
| Field | What to enter |
|---|---|
| MIDI note number | A number. Middle C (C4) = 60, A4 = 69. |
| Reference pitch A4 | In Hz |
What each result means
- Frequency = [Reference pitch A4]×2^(([MIDI note number] – 69)÷12)
- Wavelength in air (343 m/s) = 343÷[Frequency]
- Octave = floor([MIDI note number]÷12) – 1
Example values
How the main result changes when MIDI note number changes and everything else stays at the example values above:
| MIDI note number | Frequency (Hz) |
|---|---|
| 30 | 46.249 |
| 45 | 110 |
| 60 | 261.626 |
| 75 | 622.254 |
| 90 | 1,479.978 |
| 120 | 8,372.018 |
Formula
f = 440 × 2^((n − 69) ÷ 12)Worked example
Inputs — MIDI note number: 60; Reference pitch A4: 440 Hz.
Results — Frequency = 261.626 Hz; Wavelength in air (343 m/s) = 1.311 m; Octave = 4.
Frequently asked questions
What is middle C’s frequency?
About 261.63 Hz with A4 = 440 Hz.
What about A = 432 Hz?
Change the reference pitch.
What formula does the Note Frequency Calculator use?
f = 440 × 2^((n − 69) ÷ 12).