Purpose and scope
PianoTuner.io helps people observe and document the pitch of individual piano keys. The main meter covers all 88 keys from A0 through C8. The guided survey keeps several numeric readings, and the frequency chart exposes every calculated target.
The site is intentionally a pitch-checking and reference tool. It does not claim to replace a piano technician or provide a complete tuning curve for a specific acoustic piano.
Calculation and detection method
Microphone samples are processed in a browser Web Worker with autocorrelation. The interface averages a short rolling window of frequency readings to reduce visual jitter, then maps the result to the nearest key in the 88-key range.
Target frequencies use 12-tone equal temperament: frequency = A4 × 2((MIDI − 69) / 12). Changing the A4 reference recalculates every key. The interface shows both measured frequency and cents difference so visitors can inspect the underlying numbers rather than only a green or red status.
The pure calculation functions are covered by deterministic checks for the 88-key boundaries, chromatic note mapping, alternate A4 references, cents, median, and spread.
Measurement limitations
- A piano tone contains many partials. A phone or laptop microphone can lock onto a partial or octave instead of the fundamental.
- Room noise, other sounding strings, the key's attack, and microphone processing can move or destabilize a reading.
- Acoustic piano strings are inharmonic, so technicians use instrument-specific octave stretch rather than one mathematical equal-temperament table.
- The meter does not assess separate strings in a unison, tuning pin stability, action regulation, voicing, humidity history, or structural condition.
- A large pitch change alters tension across the entire piano. Consult a qualified technician before adjusting tuning pins.
Microphone privacy
Microphone audio is analyzed locally with browser audio APIs. PianoTuner.io does not record, upload, or store that audio. Numeric survey readings stay in the current page until it is reset or closed. The site separately uses analytics and advertising services described in the privacy policy.
Ownership, maintenance, and corrections
John Sorrentino created and maintains PianoTuner.io as part of a collection of focused browser tools. This page and the pitch methodology were last reviewed on July 30, 2026.
To report a factual error, broken interaction, or misleading limitation, email hello@pianotuner.io. Include the page URL, the statement or behavior in question, and a source or reproduction detail when possible. Corrections are reviewed against the calculation code, the cited sources, and reproducible browser behavior.