Last updated: March 2026
How Online Guitar Tuners Work
An online guitar tuner uses your device's microphone to capture the sound of a plucked string, then applies a pitch detection algorithm to determine the fundamental frequency. This tuner uses autocorrelation analysis, the same method found in professional clip-on tuners and studio tuning software.
The detected frequency is compared against the 12-tone equal temperament (12-TET) scale to find the nearest note. The difference between the detected frequency and the target note frequency is expressed in cents -- hundredths of a semitone. A reading of 0 cents means perfect pitch. Anything within 5 cents sounds in tune to most listeners.
Unlike simple FFT-based tuners that can struggle with low guitar notes, autocorrelation tracks the waveform repetition pattern directly. This makes it more reliable for bass strings (E2 at 82 Hz) where the fundamental frequency can be weaker than the overtones. The result is accurate, stable readings even on the lowest strings.
The tuner runs entirely in your browser using the Web Audio API. No data is sent to any server. Your microphone audio is processed locally in real time and discarded immediately. Works on Chrome, Firefox, Safari, and Edge on desktop, tablet, and mobile.
For situations where microphone detection is impractical (noisy room, broken mic), reference tones let you tune by ear. Tap any string button to hear a pure tone at the exact target frequency. Match your string to the reference tone -- a skill that also trains your ear over time.
Frequently Asked Questions
How do I tune a guitar online?
Click Start Tuner and allow microphone access. Select your tuning preset (Standard EADGBE is the default). Pluck one string at a time and watch the needle gauge. Tighten the string if the needle points left (flat) or loosen it if the needle points right (sharp). When the display turns green, the string is in tune.
What tunings does this online guitar tuner support?
The tuner includes Standard (EADGBE), Drop D, Drop C, DADGAD, Open G, Open D, and Half Step Down for guitar. For bass, it supports Standard 4-string, Drop D, and 5-string tunings. For ukulele, it supports Standard (GCEA) and Low G tunings. A chromatic mode works for any pitched instrument.
Does the online guitar tuner work on mobile?
Yes. The tuner works on iPhones (Safari), Android phones (Chrome), and tablets. Tap Start Tuner to activate your microphone. For best accuracy, hold your phone 6-12 inches from the guitar and pluck the string clearly.
Why is my guitar tuner not detecting the right note?
The most common cause is background noise or multiple strings ringing at once. Mute all strings except the one you are tuning. Move to a quieter room. Pluck the string near the bridge for a stronger fundamental tone with fewer overtones. Make sure your browser has microphone permission enabled.
What does cents mean in guitar tuning?
A cent is 1/100th of a semitone. If the tuner reads +12 cents, you are 12 cents sharp (slightly above the target pitch). If it reads -8 cents, you are 8 cents flat. Most trained ears cannot distinguish differences smaller than 5 cents, so anything within that range sounds in tune.