What is guitar intonation?
Intonation describes how accurately a guitar plays in tune as you move up the fretboard. An open string can be perfectly tuned while a fretted note is sharp or flat because the string’s effective length, action, condition, and compensation are not working together correctly.
Before checking intonation
- Install strings of the gauge and type you intend to keep using.
- Let new strings stretch and stabilize.
- Tune the open strings accurately.
- Hold the guitar in normal playing position.
- Use light, consistent fret pressure and a moderate pick attack.
Do not set intonation with old, dirty, kinked, or damaged strings. Their uneven mass can produce misleading results.
How to test at the 12th fret
- Tune the open string with the microphone tuner.
- Play the 12th-fret harmonic and confirm the expected octave.
- Fret the same string at the 12th fret using normal pressure.
- Compare the fretted reading with the harmonic or exact octave target.
- Repeat the test several times before drawing a conclusion.
What sharp or flat means
| 12th-fret result | Typical interpretation | General saddle direction |
|---|---|---|
| Fretted note is sharp | Speaking length is effectively too short | Lengthen the string |
| Fretted note is flat | Speaking length is effectively too long | Shorten the string |
Saddle direction and adjustment method depend on the bridge design. Loosen tension when the manufacturer’s procedure requires it, use the correct tool, and make small changes. Acoustic saddles often require shaping or replacement rather than a simple screw adjustment.
Why perfect intonation is limited
A guitar uses straight frets and equal-tempered compromises. Fret position, string stiffness, action height, nut height, and finger pressure all affect the result. The goal is a practical balance across the neck, not mathematically perfect pitch for every note and chord.
When adjustment is not the first answer
- If every fretted note near the nut is sharp, the nut slots or fretting pressure may be involved.
- If notes buzz or the action is unstable, neck relief and action should be evaluated first.
- If the bridge has reached its adjustment limit, the setup or hardware may need professional attention.
- If you recently changed tuning or string gauge, let the complete setup settle before final intonation.