Note Frequency Calculator
Why Every Note Has an Exact Frequency
Modern instruments are tuned to a system called twelve-tone equal temperament, which divides each octave into twelve equally spaced semitones and anchors the whole system to a single reference pitch: A4 at 440 Hz. Once that reference is fixed, every other note on the keyboard has one, and only one, correct frequency. This calculator derives it directly, whether you're starting from a note name and octave or a physical piano key number.
The Formula
where n = number of semitones from A4
For piano key numbers specifically (where A4 is the 49th key from the bottom), the same relationship is expressed as f = 440 × 2^((n − 49) / 12), with n as the key number from 1 to 88.
Where This Calculation Matters
- Synth and sampler tuning — sound designers use exact frequencies to set oscillators or verify a sampled note is pitched correctly.
- Tuning by ear or by meter — instrument techs cross-check an electronic tuner's reading against the true equal-temperament value.
- Audio engineering and EQ — knowing a note's fundamental frequency helps engineers target resonances or notch problem frequencies precisely.
- Music theory and acoustics study — the doubling of frequency per octave, and the twelfth-root-of-two ratio per semitone, is foundational to understanding pitch relationships.
| Note | Frequency |
|---|---|
| A0 (piano key 1, lowest key) | 27.5 Hz |
| C3 | 130.81 Hz |
| C4 (middle C) | 261.63 Hz |
| A4 (concert pitch reference) | 440 Hz |
| C5 | 523.25 Hz |
| A5 | 880 Hz |
| C8 (piano key 88, highest key) | 4186.01 Hz |
Values computed from f = 440 × 2^(n/12); these are the standard reference figures used across tuners, DAWs, and synthesizers.
How to Use This Calculator
- Choose a calculation mode: from a note name, or from a piano key number.
- For note mode, enter the note (such as C, C#, or Db) and the octave number.
- For piano key mode, enter the key number from 1 to 88 (A0 is key 1, C8 is key 88).
- Select Calculate to get the exact frequency in Hz.
Related Calculations
To shift a known frequency by a musical interval, use the Pitch Shift Calculator, or measure the distance between two notes with the Interval Calculator.