Online Guitar Tuner

The text comes in at 6:03: we are going on in twenty, can you learn the bridge? You grab the guitar off the stand where it has sat since Sunday, and the first open chord sours the air — the whole instrument has sagged maybe a quarter tone flat, the way wood does when the heating kicks in for the season. Your clip-on tuner is in a drawer across town with a battery that died in March. The gig does not wait.

Every guitarist knows this exact evening. It repeats at campsites, in dorm rooms, at open mics, and after every string change. The instrument that stayed in tune all summer drifts the moment you need it, and the hardware designed to fix it is always somewhere else. What you carry instead — every time, without exception — is a phone or a laptop with a browser.

That is the entire reason this page exists. The tuner above uses the microphone already in your device, listens to one string at a time, and tells you which way to turn the peg — no app download, no account, no clip, no battery. Grant mic access once, pluck, adjust, repeat six times, and you are concert-ready before the text reply comes back.

An online guitar tuner is a pitch-detection tool that runs in a web tab. It listens through your microphone, measures the dominant frequency of the note you play, compares it to the nearest target note, and shows the difference in cents — a needle or a strobe-style readout that swings left for flat and right for sharp. Because the analysis happens in JavaScript on your own device, the audio never leaves it, which matters more than people think: a microphone feed is a sensitive thing to hand to a random server.

Beyond the mic mode, a good browser tuner carries a by-ear fallback: reference tones for each string, so you can tune in a loud bar or teach a beginner what in-tune actually sounds like. The combination covers both halves of tuning — the measurable one and the musical one.

What it is not: a full strobe rack unit, and it does not need to be. Guitar tolerance for tuning error is about plus or minus three cents before a trained ear notices, and this tool resolves finer than that in any room you can hold a conversation in.

Standard tuning, low string to high, is E2, A2, D3, G3, B3, E4. In hertz: 82.41, 110.00, 146.83, 196.00, 246.94, 329.63. Those numbers are not round because guitar notes are not chosen for convenience — they fall out of a single decision made about one note: A4 equals 440 Hz. Everything else is arithmetic from there.

That anchor has a history worth knowing. Orchestras fought over pitch for centuries — Baroque ensembles sat near what early-music players now call A=415, and by the late 1800s some European orchestras had inflated past 450 in a loudness arms race, forcing France to legislate A=435 in 1859. An international conference in London settled on 440 in 1939, and ISO 16 later formalized it. When your tuner aims at 82.41 Hz for the low E, it is honoring an eighty-year-old truce.

The spacing of the strings is a compromise too. Four of the five intervals between adjacent strings are perfect fourths (five semitones); the G-to-B gap is a major third (four semitones). That one odd interval is why chord shapes are playable — your standard grips exist because of it, and it is also why the B string is the one that feels weirdest when you first learn note names up the neck.

Guitars, pianos, and virtually every Western instrument since the 1700s use twelve-tone equal temperament: the octave is divided into twelve semitones of identical ratio, 2 raised to the power of 1/12 — about 1.05946. Stack twelve of those multiplications and you land exactly on the double of your starting frequency. No note is perfectly in tune with the harmonics of another; every note is equally close. The guitar's frets are cut to this system.

Tuners measure error in cents, where one cent is one hundredth of a semitone and an octave is 1,200 cents. Because the scale is logarithmic, a cent is a ratio of about 1.000577, not a fixed number of hertz. At A4's 440 Hz, one cent is roughly 0.25 Hz. Down at the low E's 82.41 Hz, one cent is about 0.048 Hz — so the same pitch error in cents is a much smaller wobble in hertz on bass strings. This is why tuners report cents instead of raw frequencies: cents are the unit your ear actually experiences.

Here is the practical math, with real numbers. If your A string is 5 cents sharp, its actual frequency is 110 × 2^(5/1200) ≈ 110.32 Hz — audible to a careful ear. If the high E reads 5 cents flat, you are at 329.63 ÷ 1.00289 ≈ 328.68 Hz. Five cents is the difference between sounding in tune at a gig and getting that look from the keyboard player.

The mic route takes under a minute once you have done it once. Work from the low E up, exactly as written here — the string order matters less than the habit of checking all six every time.

1. 1

   Allow microphone access

   Click the enable button and accept the browser prompt. The page must be served over HTTPS for the prompt to appear at all — this site is, and your audio stream stays on the device.

2. 2

   Mute what you can

   Close the door, pause the TV, and let the amp rest. Mic tuners want one voice in the room — background chatter forces the detector to guess.

3. 3

   Pluck the low E cleanly

   Use your thumb, medium volume, and let the note ring for at least a full second. Loud attacks distort; whispers starve the detector. Let the note settle for a beat before reading the meter.

4. 4

   Read the needle and correct

   Flat means wind the peg toward you (on most headstocks); sharp means unwind. Come up to pitch from below rather than down from above — peg gears settle that way.

5. 5

   Move through A, D, G, B, high E

   Same procedure per string. Rest your picking palm lightly on the strings you are not playing so only one note reaches the microphone.

6. 6

   Recheck the low E

   Tension changes across the neck pull earlier strings flat. After the high E, glance back at the low E — usually it needs a touch. This pass is the mark of someone who tunes for a living.

7. 7

   No mic? Switch to reference tones

   Tap the tone mode and match each string by ear. Slower, quieter, and it trains the muscle that mic tuners let you skip.

Inside the tab, your microphone's stream lands in a Web Audio AnalyserNode, which hands over slices of the raw waveform — typically a few thousand samples at a time. The tuner's job is to answer one question about each slice: what is the fundamental frequency? Human ears do this effortlessly; software has to be tricked into it.

The classic trick is autocorrelation. Take the waveform, compare it against a time-shifted copy of itself at every possible shift, and score how well they match. When the shift equals exactly one period of the note, the copy lines up with the original and the score spikes. Find the spike, and the period tells you the frequency: 44,100 samples per second divided by, say, 535 samples per period gives 82.4 Hz — your low E. Refinements of this idea, notably the YIN algorithm published by de Cheveigné and Kawahara in 2002, fix the octave-halving errors that plague naive versions, which is why the needle does not flicker between E and E-an-octave-up when your attack is bright.

Two guards keep the readout honest. A loudness gate ignores anything below a volume threshold, so room noise and cable hum do not register as phantom notes. A stability filter requires several consecutive slices to agree before the needle commits — one stray harmonic from a hard pick attack gets vetoed instead of yanking the display. The result is a tuner that tracks plucked notes the way a needle behaves on a good hardware pedal.

Numbers below are the exact frequencies equal temperament dictates, computed from A4=440. Use them to cross-check any tuner, including this one — if a tool tells you the A string is in tune at 108 Hz, the tool is wrong, not your ear.

That last example hides a detail pros exploit: one semitone down is a frequency ratio of 1.05946, so D2 is 82.41 divided by that, 73.42 Hz. Any retune on the guitar is multiplication or division by 1.05946 per fret. Half-step-down bands tune everything from this same table: E♭2 at 77.78, A♭2 at 103.83, D♭3 at 138.59, G♭3 at 185.00, B♭3 at 233.08, E♭4 at 311.13.

Print this or memorize the hertz column — it settles every argument about what 'in tune' means. String numbers follow the convention where the high E is string 1.

The odd one out in the interval column deserves its sentence: five of the six string gaps are fourths, but G3 to B3 is a third. Fret the B string at the fourth fret and it matches the open G's octave; every other string matches at the fifth. This asymmetry is the tax chord players pay so that a first-position E-major shape is physically possible. Blame the luthiers of the 1700s — it was the right trade.

Clip-on tuners read vibration through a piezo contact sensor clamped to the headstock, which makes them nearly immune to room noise — the reason stage techs love them. Their weakness is accuracy at the extremes and the battery you forgot. Pedal tuners mute your signal and do one job brilliantly but live on a pedalboard you did not bring. Phone apps are microphones with software, same as this page, plus ads and a permission appetite.

Strobe tuners — the spinning-disc descendants of Conn's 1936 design — resolve well under a cent and are what piano and banjo techs use for setups. For guitar, that precision exceeds the instrument itself: fret placement, string age, and neck relief each introduce errors larger than a strobe can resolve. A cent-accurate browser tuner is matched to the actual tolerance of the machine you are holding.

And then there is tuning by ear, the oldest method and still the best training. The classic relative method uses harmonics: touch the low E string over the fifth fret (not pressing) and pluck — you hear E4 — then touch the A string over the seventh fret for the same-sounding harmonic, and match them. Repeat down the strings. One honest wrinkle: the fifth-fret harmonic of E rings at exactly four times 82.41 = 329.63 Hz, while the A string's seventh-fret harmonic rings at three times 110 = 330.00 Hz. Equal temperament makes those 1.9 cents apart, so perfect matching leaves you a hair sharp. Educated ears tune the compromise deliberately.

The chromatic detector does not care what string you play — it just reports pitch. That makes it a tuner for every dialect of the instrument, and there are dozens. A few you will actually use:

• Drop D (DADGBE): low E down a whole step to D2 at 73.42 Hz. One-string change, one-finger power chords, the foundation of rock from the 1990s forward.
• Half-step down (E♭ standard): every string flat one semitone — 77.78 to 311.13 Hz. The sound of blues-rock vocalists who needed the melody lower.
• Open G (DGDGBD): the Keefe/Richards tuning; a strum of open strings is already a G chord.
• DADGAD: the folk and Celtic tuning; droning fourths and a suspended shimmer, impossible tension in standard.
• Open D (DADF#AD): slide guitar's home turf; the barre at the 12th fret is a full D chord.
• Bass standard (EADG, an octave down): E1 at 41.2 Hz — reachable by this tuner's math, though a clip-on reads it more reliably through a laptop mic.

Retuning technique matters more in alternates. Change strings one at a time from standard, recheck earlier strings after each big tension move, and expect the neck to move a little — a guitar is a wooden spring, not a brick. Give it thirty seconds between the drop and the fine tune.

A string's pitch depends on three things: its tension, its length, and its mass per unit length. Change any one and the note moves. That is the whole physics, and it explains every tuning headache you have ever had. New strings stretch under tension for the first day or two — mass and length barely move, but the core temporarily gives, so pitch sags until the metal settles into its working shape. That is why the first tune-up after a string change lasts twenty minutes and the next morning's lasts two.

Temperature is the second thief. Metal expands when warm, wood moves with humidity, and they move at different rates. Take a guitar from a cold car trunk into a warm club and the neck shifts within minutes — relief changes, string height changes, and the fretted notes land a few cents off their open-string targets. Professional touring techs let instruments acclimate for an hour before the tuning that counts, then tune again right before the downbeat.

The third is playing style itself. Hard picking bends the string sharp for the instant it rings; bends and vibrato physically stretch the string a hair past its resting length; and a capo clamped two tight drags every note under it sharp. None of this is the tuner's fault. The habit that beats all three: tune, play a song, tune again, and trust the second reading. Guitars are wooden machines under 100-plus pounds of combined string pull — staying in tune is a negotiation, not a setting.

The permission wall comes first. If the mic prompt was dismissed — accidentally or on purpose — the browser remembers, and the tuner waits forever for audio it will never receive. Click the lock or tune icon in the address bar, set Microphone to Allow, reload, and the prompt returns. On iOS, mic access also requires the browser itself to have camera-and-microphone permission in Settings; check Settings → Safari if the prompt never appears.

Noisy rooms produce the jumping needle. The detector picks the loudest periodic thing it hears, and a conversation, a fan, or a television can beat your guitar. Palm-mute the other five strings, play closer to the twelfth fret where fundamentals dominate, and if it still fights you, switch to reference tones and let your ears do the discriminating. Studios tune this way on purpose.

Two hardware quirks: ancient Bluetooth headsets can mangle the microphone path with aggressive noise cancellation that deletes steady tones — including the note you are playing. And very quiet laptops sometimes ship mics that roll off below 100 Hz, making the low E read an octave high (the detector locking onto 164.8 Hz, the second harmonic). Both problems vanish with a wired connection or the nearest clip-on.

Beginners, first: a free tuner removes one of the three barriers on night one — you cannot practice a chord if the guitar is not in tune, and clip-ons get lost exactly when enthusiasm is fragile. Teachers assign this page as the one tool every student already owns. Campfire players, open-mic regulars, and anyone whose tuner battery follows Murphy's law keep the bookmark.

Beyond guitar: ukulele groups tune ensembles with it, banjo and mandolin players use chromatic mode, bouzouki and charango players less often but with the same success. Even synth owners use it to confirm an oscillator against A440. Any instrument with a stable pitch and a microphone in reach is fair game.

Once you are in tune, the metronome is the practice partner that makes tuning matter. Recording a quick take afterward? The Online Voice Recorder captures ideas without uploading them, and it is the honest way to hear whether your tuning held up under pressure.