Online Guitar Tuner with Microphone

A plucked string produces a waveform that repeats. The tuner's whole job is to measure how long one repetition takes, because the reciprocal of that time is the frequency.

Finding the repeat is harder than it sounds. A guitar string does not produce a clean sine wave; it produces a fundamental plus a stack of harmonics, and the shape changes as the note decays. The tuner compares the incoming waveform against a delayed copy of itself and looks for the delay at which the two line up best. That delay is the period.

One detail decides whether the reading is trustworthy. A naive comparison scores long delays worse than short ones simply because fewer samples overlap, which biases every result toward higher frequencies and makes the low strings read sharp. Normalising the comparison by the energy actually present at each delay removes that bias, which is why a low E reads the same 82.41 Hz as a high E reads 329.63 Hz.

The detector also reports how strongly the window repeats at all. When that confidence is low, because the room is noisy or the string has died away, the gauge shows nothing rather than guessing. A tuner that always displays a number is not more accurate, it is less honest.

This is also why one string at a time works and strumming does not. Six notes together have no single repeating period, so there is nothing for the detector to lock onto. Pluck one string, let it ring, read the needle.

The needle shows cents, not Hertz. A cent is one hundredth of a semitone, and using it means the same needle deflection represents the same musical error everywhere on the instrument, which Hertz would not.

The gauge has two zones. Orange marks roughly ±22 cents, which is noticeably out of tune but recognisably the right note. Green marks ±5 cents, and inside it the readout stops showing a number and simply says the string is in tune. That is deliberate: at that precision the exact figure is dominated by how the string is decaying rather than by how it is tuned, so a number would imply accuracy that is not there.

Within 5 cents on every string, a full chord sounds clean to nearly every listener. Chasing zero is wasted effort.

The direction tells you which way to turn. A negative reading, needle left, means flat: the string is below pitch and needs tightening. A positive reading, needle right, means sharp and needs loosening. If reading -20 cents on the low E, tighten slowly and watch the needle climb toward the middle.

Turn the peg in small increments and re-pluck between them. Tuning pegs have backlash and strings need a moment to settle, so a continuous turn while watching the needle overshoots almost every time. The note and the cent readout sit below the needle's pivot so the needle never crosses them, which means you can watch both at once while your other hand is on the peg.

Standard tuning is E2 A2 D3 G3 B3 E4 from the thickest string to the thinnest. The numbers are octaves in scientific pitch notation, so the two E strings are two octaves apart: E2 at 82.41 Hz and E4 at 329.63 Hz.

String numbering runs the opposite way to thickness, which trips up beginners constantly. The first string is the thinnest, the high E. The sixth string is the thickest, the low E. Guitar tab, chord charts and this tool all follow that convention, so a reference to the sixth string always means the bass E.

The open A string reads A2, which at standard pitch is exactly 110 Hz. That is a useful number to remember because it is the one reference tone most people can hum.

The reference panel plays each of the six notes as a pure sine tone. Tuning by ear against it is a genuinely different skill from watching a needle, and worth practising for two reasons. It works when the room is too noisy for the microphone, and it trains you to hear beating, the slow pulsing that appears when two pitches are close but not identical. As the string approaches the reference, the beating slows down; when it stops, the string is in tune.

Play the tone, pluck the string, and listen for that pulse rather than trying to judge the pitches separately. The beat rate is far easier to hear than a small pitch difference.

Order matters, and the reason is mechanical. Every string pulls on the neck, so tightening one changes the tension the others are working against. Tuning six strings in one pass leaves the first ones you tuned slightly off by the time you finish.

Start with the low E, the thickest string, and work toward the thin ones. Then do a second full pass in the same order. The second pass is where the guitar actually gets in tune, and it is usually much faster than the first because the corrections are small.

Always arrive at the note from below. If a string is sharp, loosen it past the target and then tighten up to it. Approaching from below leaves the string seated properly in the nut slot and the tuning peg under tension, so it holds. Tuning down to a note leaves slack in the mechanism that works its way out during the first minute of playing, which is why a guitar tuned downward drifts almost immediately.

Pluck with normal playing force, not harder. A hard pluck stretches the string momentarily and can read 10 cents sharp for the first instant before settling. Tuning to that initial spike leaves the string flat once it settles.

New strings need several passes and a stretch. Pull each string gently away from the fretboard, retune, and repeat until it stops going flat. Until that settles, no amount of careful tuning will hold for a whole song.

Tuning down to the target is the most consequential. It feels equivalent to tuning up and it is not, because the slack it leaves in the peg and the nut works out under playing tension and the string drops flat within minutes.

Plucking too hard comes second. The pitch spike on a hard attack is real and can reach 10 cents, so tuning to the attack rather than the sustain leaves the string flat where it matters.

Expecting a still needle is a misreading of what a decaying string does. The pitch genuinely drifts as the amplitude falls, and the needle is reporting that honestly. Read the needle a moment after the attack, once the note has settled but before it fades, and accept a little movement.

A noisy room makes the tuner go quiet rather than wrong. If the gauge keeps returning to the listening state, the detector is refusing to guess. Move closer to the device, play a little louder, or use the reference tones and tune by ear instead.

Strumming while tuning cannot work. Multiple notes have no single period to detect, so the reading either jumps between strings or vanishes.

Two smaller ones worth naming. A capo left clamped on pulls strings slightly sharp, so tune in the state you will play in. And a string that will not hold pitch at all, or reads fine open but sharp at the twelfth fret, is telling you about worn strings or intonation at the bridge rather than about tuning.