One octave above A4
With A4 = 440 Hz, 880 Hz maps to A5 exactly. Doubling frequency adds 12 equal-tempered semitones.
Nearest equal-tempered noteA4
440.000000 Hz · MIDI 69
+0.00 cents · On the reference pitch
12-tone equal temperament. Scientific octave numbering: middle C is C4; A4 is MIDI 69. Alternate octave labels on hardware do not change frequency.
Preview is a quiet sine tone, limited to 20–20,000 Hz. Start at low device volume. A4 = 432 or 442 is an optional tuning reference, not a claim of a different tuning system.
Your inputs and generated files are processed locally in your browser. No input is uploaded to an audio or text-processing service.
How to use the Frequency to Note Converter
- 01
Choose frequency-to-note or note-to-frequency mode.
- 02
Enter a frequency in hertz, or a note with octave such as C4, F#3, or Bb5.
- 03
Set the A4 reference, review the nearest note and cents, then copy the result or play the nearest pitch.
Examples
A slightly sharp reference
At A4 = 440 Hz, a 445 Hz input is approximately +19.56 cents above A4. Changing the reference to 445 Hz makes that input exactly A4.
The frequency formula
For MIDI note number m and reference A4 frequency a, f = a × 2^((m − 69)/12). In the other direction, m = 69 + 12 × log2(f/a). The nearest integer MIDI number identifies the nearest equal-tempered pitch.
Reading cents deviation
A cent is one hundredth of an equal-tempered semitone. The result is 100 times the difference between the fractional MIDI value and its nearest integer. Positive means sharp; negative means flat. At an exact halfway point, rounding chooses the upper note.
Octaves, references, and enharmonic names
Scientific pitch notation labels middle C as C4 and standard tuning A as A4, MIDI 69. Sharp and flat names denote the same pitch class here. The A4 reference may range from 400 to 480 Hz; choosing another reference shifts all frequencies proportionally and does not change the equal-temperament ratios.
What to know
- Twelve-tone equal temperament only; not just intonation or a spectrum analyzer.
- Preview output is not acoustically calibrated.
Common questions
Does this analyze microphone audio?
No. Enter a known frequency or note name. The instrument tuner is the separate tool for live pitch detection.
Are C# and Db different frequencies?
In the twelve-tone equal-tempered model used here they share a frequency. Other tuning systems can treat enharmonic notes differently.
Why is the MIDI octave different on my keyboard?
Manufacturers may label middle C with a different octave number. The underlying MIDI note number and frequency can still agree.
What ranges are supported?
Frequency input supports 5–24,000 Hz. Note entry supports MIDI 0–127, from C-1 through G9 including single accidentals. Preview is limited to 20–20,000 Hz; frequencies outside MIDI range can still be labeled mathematically.