Online guitar tuner – for every stringed instrument

This online guitar tuner listens to the string through your microphone and measures its fundamental frequency. From that it works out the note and how many cents it is off. A half step is 100 cents, so a reading of −20 means the string is a fifth of a half step flat.

Several steps keep it reliable on low strings and in noisy rooms:

• Filtering: hum and hiss outside your instrument's range are filtered out of the microphone signal.
• Pitch detection with an autocorrelation method (the McLeod pitch method), using a window twice as long for bass guitar and double bass, so even a 31 Hz low B reads accurately.
• Noise gate and smoothing: silence and pick noise are ignored, and a median filter removes outliers so the needle doesn't jump around.
• Octave correction: a string's overtone is sometimes louder than its fundamental. When a reading is exactly an octave or a twelfth away from the string you're tuning, the tuner recognises it and measures against the right string.

Only your browser analyses the microphone sound – nothing is recorded or uploaded.

The big letter is the nearest note with its octave number. Below it you'll see the frequency in hertz and the offset in cents.

• The needle swings between −50 and +50 cents. It's red when you're far off, amber within 10 cents and green within 3 cents – a difference your ear can't hear.
• The strobe stripes work like a pro strobe tuner: they drift left when you're flat and right when you're sharp, faster the further off you are. When they stand still, the note is spot on. For fine-tuning, the stripes are easier to follow than the number.
• When a string stays in tune for about a second, it gets a check mark. Once every string has one, you're done.

The row of buttons shows the strings of the selected tuning, thickest on the left, numbered the usual way (string 1 is the thinnest). Tap a string to hear its reference tone with a realistic plucked-string sound; the tuner then locks onto that string, which helps when a string is so far off that it would be mistaken for its neighbour.

These guitar tunings are built in (low to high, at A4 = 440 Hz):

Standard tuning frequencies: E2 = 82.41 Hz, A2 = 110.00 Hz, D3 = 146.83 Hz, G3 = 196.00 Hz, B3 = 246.94 Hz, E4 = 329.63 Hz.

It isn't just a guitar tuner. Instruments and tunings available:

Chromatic mode recognises any note – use it for wind instruments, singing, checking a piano, or any tuning that isn't on the list.

Tuning is measured against A4. Today's standard is 440 Hz, but many orchestras tune to 442 Hz, baroque music is often played at 415 Hz, and some players prefer 432 Hz. Use the slider to set anything from 415 to 466 Hz – reference tones and string frequencies follow it.

If you're perfectly in tune but sound off against a piano, organ or recording, the other instrument is probably at a different reference pitch. Measure the piano's A in chromatic mode and set the reference to match.

• Always tune up to the note. If a string is sharp, drop it below the note and bring it back up, so the peg doesn't slip back.
• Pluck once, firmly, and let it ring. The first instant of a note is slightly sharp; the needle settles after half a second.
• Go round twice. Tightening one string bends the neck a little, so after the first pass the others may be a few cents off – especially with open tunings and new strings.
• New strings stretch for a few days and need frequent retuning. Gently stretching them speeds this up.
• On a phone, hold it close to the instrument (near the sound hole or the headstock) and turn off background music. The screen stays awake while the tuner is listening.
• If the reading flickers between two notes, another string is probably ringing. Mute the other strings, or tap the string you're tuning to lock onto it.