Guitar Intonation Checker

How to Check Your Intonation

1. Put on the strings you play and tune to pitch with the tuner. Sit the way you normally play, because the neck relief changes slightly when the guitar is held.
2. Choose your tuning, start the microphone, and press Check this string on string 6.
3. Play the 12th-fret harmonic: touch the string lightly directly above the 12th fret wire, pluck firmly, and lift your finger. Let it ring until the bar fills.
4. When it says got it, mute the string. Two seconds later it listens for the fretted 12th. Press just behind the 12th fret with normal pressure and let it ring.
5. Read the result. The number is the fretted note minus the harmonic, in cents, with the direction to move the saddle if you need to. Repeat for each string.

A clip-on or nearby phone microphone works fine for an acoustic. For an electric, play through a small amp near the device, or close to the mic unplugged in a quiet room.

What the Numbers Mean

Each card shows three readings. Harmonic is how far the harmonic is from the ideal octave. If it is more than a few cents off, the open string is out of tune; retune it before going on. Fretted 12th is the same measurement for the fretted note. The headline figure is the difference between the two, and that is the intonation:

• Within ±3¢: good. Leave it alone.
• Positive (sharp): the string is too short. Move the saddle back, away from the neck.
• Negative (flat): the string is too long. Move the saddle forward, toward the neck.

A useful rule of thumb on many electric bridges is that a full turn of the intonation screw moves the reading a few cents. It varies with the bridge and the string, so make small adjustments and measure again rather than turning a lot at once.

Why Fretted Notes Go Sharp

In theory, the 12th fret sits exactly halfway along the string, so the fretted note is an exact octave. In practice, pressing a string down to the fret stretches it slightly, and stretching raises the pitch. Thicker strings stretch more and bend less easily, so they need extra length to compensate. That is why the saddles on a well-set-up electric form a slanted, stepped line, with the wound strings set further back.

Anything that changes how far the string has to travel to the fret changes intonation: a higher action, a heavier gauge, a lower tuning, or more neck relief. So after a change of string gauge, a drop tuning, or an action adjustment, check intonation again. The string tension calculator shows how much a tuning or gauge change alters the load on each string.

Adjusting the Saddles

On most electric guitars and basses, each saddle has a screw at the back of the bridge. Turning it moves that saddle forward or back. Detune the string slightly before moving the saddle, since that is kinder to the saddle and the string, then tune back up and measure again. Make small moves. Go through all six strings, then do a second pass. Adjusting one string can shift the others slightly through the bridge and neck.

The intonation guide covers the whole job in more detail, including Tune-o-matic bridges, Telecaster barrel saddles, and when to leave it to a technician.

Getting a Clean Reading

• Work in a quiet room. Any background note, such as a fridge hum or music, can confuse the reading.
• Pluck at your normal strength. Very hard plucks start sharp; the checker ignores the attack, but a gentle, even pluck helps.
• Do not squeeze the fretted note. Press only as hard as you would to play it. Extra pressure pushes the note sharp and gives a false result.
• Measure a string twice if a result surprises you. Two readings within a cent of each other can be trusted.

Audio is processed entirely in your browser and never recorded or uploaded. Results are saved on this device for each tuning, so you can adjust a saddle, come back later, and re-check just that string.