Guitar Intonation: Check Sharp and Flat Fretted Notes
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Intonation is how well a guitar stays in tune as you play higher up the neck. If chords sound fine near the headstock but sour higher up, intonation is a likely cause. You can check it with a tuner in a few minutes.
Before You Check
Intonation depends on the rest of the setup. Get these right first:
- Fresh strings in the gauge you plan to keep
- The tuning you actually play in
- Neck relief and action already set
Changing the tuning, string gauge, or action can throw intonation off. A check done before those changes may not hold afterward. Our guitar setup guide lists the full order.
How to Check Intonation
- Tune the open string with a tuner.
- Play the 12th-fret harmonic or the open string and note the reading. A harmonic is the chime you get by touching the string lightly over the fret wire without pressing it down.
- Fret the same string at the 12th fret, pressing lightly. Pressing hard can bend the note sharp and give a false reading.
- Compare tuning accuracy: the fretted 12th should be one octave above the open string, or the same pitch as the 12th-fret harmonic. Compare the tuner’s sharp or flat offset, not identical frequencies with the open string.
- Repeat for every string.
Reading the Result
The speaking length is the part of the string that vibrates, from the nut to the saddle.
| Fretted 12th compared with open string or harmonic | Usual meaning | General fix |
|---|---|---|
| Matches | Intonation is close | No change needed |
| Sharp | Speaking length is too short | Make the speaking length longer |
| Flat | Speaking length is too long | Make the speaking length shorter |
To make the speaking length longer, move the point where the string rests on the saddle away from the nut. To make it shorter, move it toward the nut. How you do that depends on the bridge. Screw direction, how you reach the saddle, and how far it can move all differ between designs. Check how your bridge works before you turn anything.
Adjust in Small Steps and Retune Every Time
Moving a saddle changes the pitch of the open string, so:
- Make a small adjustment.
- Retune the open string.
- Check the fretted 12th again.
- Repeat until the readings match as closely as you can get them.
Skipping the retune is a common reason intonation never seems to settle.
Worked Example
A player tunes the G string, then frets it lightly at the 12th fret. The tuner reads sharp. Sharp means the speaking length is too short, so they move the G saddle a small amount away from the nut, retune the open string, and check again. The fretted note is now closer. One more small move and retune brings the two readings into line. Then they move on to the next string.
Later the player switches to a heavier set of strings. They recheck every string, since changing gauge affects intonation. The string tension calculator can help compare string tension when you change gauges.
Intonation is only one reason chords can sound sour. If your 12th fret readings already match, our guide to why a guitar sounds out of tune covers other causes, such as old strings, the nut and the tuning pegs. When a new set of electric guitar strings is behind the change, the guitar string tension guide explains what tension means as you compare sets.
Acoustic Guitars
Most acoustic guitars have a fixed saddle with no adjustment screws. You can still check intonation the same way. If it is off, fixing it usually means reshaping or replacing the compensated saddle, or other bridge work. A compensated saddle has a shaped top that sets a slightly different length for each string. This is a job for a professional technician.
Fender’s intonation guide describes the harmonic-versus-fretted check. Consult your bridge’s instructions for how to change speaking length.
