How it works
The microphone signal is analysed about 20 times a second with the YIN pitch detector, an improved autocorrelation method: it compares the sound with delayed copies of itself, finds the delay at which the wave repeats, and turns that period into a frequency. A short median filter steadies the reading.
The frequency is then placed on the 12-tone equal-tempered scale with A4 = 440 Hz, the international standard pitch of ISO 16. The needle shows how far you are from the nearest note (or the nearest string of the chosen instrument) in cents, where 100 cents make one semitone. Within ±5 cents it turns green.
Standard tunings
The tuner recognises these strings automatically. Change the calibration if your band or orchestra tunes to a different A, such as 442 Hz.
| Instrument | Strings (low to high; ukulele in re-entrant order) |
|---|---|
| Guitar | E2 A2 D3 G3 B3 E4 |
| Ukulele | G4 C4 E4 A4 |
| Bass | E1 A1 D2 G2 |
f = A4 × 2^((n − 69) ÷ 12) · cents = 1200 × log₂(f ÷ f₀)
Tips
- Pluck one string at a time with medium force and let it ring; mute the others so they do not confuse the reading.
- Tune up to the note: if you are sharp, go below the note first and then come back up, so the string stays in tune longer.
- In a noisy room move the phone or laptop close to the instrument, or use a headset microphone near the sound hole.
Standards and sources
- ISO 16:1975 Acoustics: standard tuning frequency (A = 440 Hz) · ISO
- de Cheveigné & Kawahara 2002, YIN, a fundamental frequency estimator for speech and music · J. Acoust. Soc. Am.
- Web Audio API · W3C Recommendation
- Media Capture and Streams (getUserMedia) · W3C
- AnalyserNode · MDN Web Docs
Last reviewed October 18, 2026
Frequently asked questions
Why does the tuner ask for my microphone?
It has to hear your instrument to measure its pitch. The sound is processed live in your browser and is not recorded, stored or uploaded. You can stop it at any time with the Stop button or by closing the page.
How accurate is it?
With a clear single note the reading is typically within one or two cents, which is finer than most people can hear. Background noise, several strings ringing at once or a very weak signal make it less stable.
What does the A4 calibration do?
It moves the whole scale. The international standard is A4 = 440 Hz; some orchestras use 442 or 443 Hz, and older recordings may sit lower. All notes and string targets follow the value you set.
What is a cent?
A hundredth of a semitone. +10 cents means slightly sharp (too high), −10 cents slightly flat (too low).