What Guitar Intonation Is and Why It Matters
Intonation is how accurately each fret on your guitar produces the correct pitch. When intonation is off, the same note sounds sharp (higher than it should) or flat (lower than it should) depending on which fret you play it on. A guitar can be perfectly in tune when you play open strings, but sound out of tune the moment you fret a note—that is an intonation problem, not a tuning problem.
Most intonation issues come from the bridge saddle position or the length of the strings themselves. On electric and acoustic guitars, you adjust intonation by moving the bridge saddle backward or forward, which changes how long the vibrating part of the string is. On classical guitars with fixed bridges, intonation is usually set at the factory and cannot be adjusted without professional help.
You will need a digital tuner that shows you whether each fretted note is sharp or flat. A clip-on tuner works well and costs between $15 and $40. You will also need an Allen wrench or screwdriver—the size depends on your guitar's bridge type, usually 1.5mm to 3mm.
Key Takeaways
- Intonation is adjusted by moving the bridge saddle forward or backward, which changes the effective length of each string.
- You measure intonation by comparing the pitch of the open string to the pitch of the same note played at the 12th fret using a digital tuner.
- If the 12th fret is sharp, the saddle moves backward; if it is flat, the saddle moves forward.
- Each string is adjusted individually, and the process takes 15 to 30 minutes for a full setup.
- Some bridge types (like Fender-style bridges) adjust one saddle at a time, while others (like Gibson-style) adjust all strings together.
How to Measure Intonation with a Tuner
Tune your guitar to pitch using your tuner. Then, with the tuner still active, pluck the open string (unfretted) and note the reading. Next, fret that same string at the 12th fret and pluck it again. The 12th fret should produce the same note name as the open string, but one octave higher.
Your tuner will show you whether the 12th fret note is sharp, flat, or in tune. If it reads sharp, the fretted note is higher than it should be. If it reads flat, the fretted note is lower than it should be. Write down which strings are sharp and which are flat—you will need this information when you adjust the saddle.
Repeat this test for all six strings. Most guitars will have at least one or two strings that need adjustment. It is normal for some strings to be slightly off, especially on older guitars or those that have not been set up in a while.
Adjusting Saddles on Fender-Style Bridges
Fender Stratocasters, Telecasters, and similar guitars have individual saddles that move forward and backward on a bridge plate. Each saddle has a small screw on the back (or sometimes on the side) that you turn to move it.
If the 12th fret is sharp, turn the screw counterclockwise to move the saddle backward, away from the neck. This makes the string longer and lowers the pitch. If the 12th fret is flat, turn the screw clockwise to move the saddle forward, toward the neck. This makes the string shorter and raises the pitch. Make small adjustments—a quarter turn at a time—and retest with your tuner after each adjustment.
Work on one string at a time. After adjusting, retune the open string and check the 12th fret again. Once that string reads in tune at both the open position and the 12th fret, move to the next string. The entire process usually takes 20 to 30 minutes for all six strings.
Adjusting Saddles on Gibson-Style Bridges
Gibson Les Pauls and similar guitars have a bridge with saddles that sit on a bridge plate. The saddles do not move individually—instead, you adjust the bridge plate itself by turning two screws at the back of the bridge. One screw raises or lowers the bass side (low E, A, D strings), and the other adjusts the treble side (high G, B, E strings).
This design means you cannot fine-tune each string separately. If the bass strings are sharp and the treble strings are flat, you have a conflict and will need to find a compromise. However, if all strings on one side are consistently sharp or flat, you can adjust that side independently.
Turn the screws very slowly—a quarter turn makes a noticeable difference. Retune and retest after each small adjustment. If you find that one side needs to move forward and the other backward, you may need to shim the bridge or have a technician adjust the nut, which is beyond a basic setup.
Adjusting Saddles on Acoustic Guitars
Most acoustic guitars have a bridge saddle that is glued in place and cannot be moved without removing it. If your acoustic needs intonation adjustment, the saddle must be removed, sanded, or replaced—this is a job for a repair technician, not a home adjustment.
However, some acoustic guitars have compensated saddles, which have a stepped or angled top surface designed to improve intonation across all strings. If your acoustic has a compensated saddle and intonation is still off, the saddle may need to be replaced with a new one shaped to your guitar's specific bridge.
If your acoustic is consistently sharp or flat across all strings, the problem may be the nut rather than the saddle. Nut work also requires professional help. A repair shop can evaluate whether your acoustic needs a new saddle, a new nut, or both.
Common Mistakes That Make Intonation Worse
The most common mistake is adjusting the saddle too much at once. A quarter turn of the adjustment screw can move the saddle 1 to 2 millimeters, which is enough to change the pitch noticeably. If you turn the screw a full rotation, you may overshoot and have to turn it back, wasting time and risking damage to the screw or saddle.
Another mistake is forgetting to retune the open string before checking the 12th fret. If the open string drifts sharp or flat while you are working, your 12th fret reading will be wrong. Retune to pitch every time before you test.
Do not assume that all strings need to move in the same direction. Each string is independent. One string might be sharp while another is flat, and they each need their own adjustment. Also, do not confuse intonation with action (string height). Raising or lowering the bridge changes action, not intonation—only moving the saddle forward or backward changes intonation.
When to Stop and Call a Technician
If you have adjusted the saddle as far as it will go in one direction and the string is still sharp or flat, stop. Pushing the saddle to its limit can damage the bridge or cause the saddle to slip. This usually means the bridge itself is misaligned or the nut needs adjustment—both are technician jobs.
If your guitar has a fixed bridge (like a classical guitar or some acoustic models), intonation cannot be adjusted at home. A technician can shim the bridge or replace the saddle, but these are not DIY tasks.
If you are uncomfortable using tools or unsure whether you are making progress, a professional setup costs between $50 and $150 and takes one to two hours. A technician can also check whether your intonation problem is actually a nut or bridge issue that requires more involved work.
Frequently Asked Questions
Why does my guitar sound in tune on open strings but out of tune when I fret?
That is intonation, not tuning. The open strings are in tune, but the fretted notes are not because the saddle position is off. Moving the saddle forward or backward changes the effective length of the string and fixes the pitch at the frets.
Do I need to adjust intonation after changing string gauge?
Yes. Thicker or thinner strings have different tension and vibration characteristics, which can shift intonation. After putting on new strings, let them settle for a day, then retune and check intonation. You may need to make small saddle adjustments.
Can I adjust intonation on a classical guitar?
Not without professional help. Classical guitars have fixed bridges that are glued on, and the saddle cannot be moved. A technician can shim the bridge or replace the saddle, but these require removing the bridge and are not home adjustments.
What if my saddle is already at the front or back limit and the string is still out of tune?
This usually means the nut or bridge is misaligned, or the frets themselves are worn. Stop adjusting and take the guitar to a technician. Pushing the saddle beyond its range can damage the bridge.
How often should I check and adjust intonation?
Check intonation every few months or after changing strings. Most guitars stay in intonation for months at a time if the neck is stable and strings are not damaged. Seasonal changes in humidity can shift intonation slightly, so a quick check in spring and fall is a good habit.