How to Intonate a Guitar

Getting a guitar perfectly “in tune” isn’t just about the open strings—it’s about playing in tune everywhere on the neck. That’s what intonation sets: the relationship between your open string and the fretted notes up the board. Below is a bench-tested walkthrough for both electric and acoustic guitars, so you can dial in clean octaves, solid chords, and accurate leads.

What Intonation Is (And Why It’s the Last Step)

Intonation is the process of matching each string’s open pitch to its fretted octave (most commonly checked at the 12th fret). If the fretted octave reads sharp, the vibrating length is too short; if it reads flat, the vibrating length is too long. You correct that by changing string length—on electrics by moving individual saddles, and on acoustics by changing the contact point on the saddle. Always intonate after you’ve installed fresh strings, set neck relief (truss rod), and dialed in action. Any setup change you make later will move the goalposts.

Bench Prep (For Any Guitar)

Install fresh strings and stretch them in.
Set relief with a truss rod wrench so the neck has appropriate curvature.
Set action to your target height.
Tune to pitch with a precise tuner (a strobe is ideal).
Check in playing position. Gravity and even pickup pull can skew readings if the guitar lays flat.

Pro tip: Use a consistent, medium pick attack when testing. A heavy attack can momentarily “overshoot” sharp and then decay into tune.

How to Intonate an Electric Guitar

Electric guitar bridges give you per-string control. You’ll compare the open (or 12th-fret harmonic) to the fretted 12th-fret note and adjust the saddle until they match exactly, one octave apart. Work string-by-string and re-tune after every adjustment.

Tools You’ll Want On The Bench

A reliable chromatic/strobe tuner, the correct screwdriver or Allen key for your bridge, and a fresh set of strings. Keep a small ruler or string action gauge handy to confirm action if readings look strange.

How To Test Each String

Tune the open string to pitch.
Lightly chime the 12th-fret harmonic and confirm it’s on pitch (helpful for stable reading).
Fret the 12th-fret note and compare to the reference (open or harmonic).

Fretted 12th sharp ➜ lengthen the string.
Fretted 12th flat ➜ shorten the string.

Memory device: “Flat forward, sharp back.” If the 12th is flat, move the saddle toward the nut (forward). If it’s sharp, move the saddle toward the tail/bridge (back). Make tiny moves, re-tune, re-check.

Common Bridges & Which Way To Turn

Fender-Style (Strat/Tele) with Screw-Adjusted Saddles

12th sharp → turn the screw clockwise to move the saddle back (lengthen).
12th flat → turn the screw counterclockwise to move the saddle forward (shorten).

Gibson-Style Tune-O-Matic (Screws Forward Towards the Saddle)

12th sharp → turn the screw counterclockwise move the saddle back (lengthen).
12th flat → turn the screw clockwise to move the saddle forward (shorten).

Gibson-Style Tune-O-Matic (Screws Back Towards the Tailpiece)

12th sharp → turn the screw clockwise to move the saddle back (lengthen).
12th flat → turn the screw counterclockwise to move the saddle forward (shorten).

(Direction at the screwdriver can look “reversed” depending on which side the screw is accessed—watch the saddle, not the screwdriver.)

Floyd Rose / Locking Tremolos

Use an Allen wrench instead of a screwdriver to adjust the saddle position. Loosen string/lock as needed and slide the saddle to change length; work slowly to avoid stripping hardware. Re-tune after every micro-move.

Accuracy Tips & Troubleshooting

Always check with the guitar in playing position; pickup magnet pull and gravity matter.
If a saddle runs out of travel, re-check relief and action—high action makes fretted notes trend sharp.
If intonation won’t settle, inspect for high frets, worn strings (especially those dented by the frets), or extreme gauge changes.

How to Intonate an Acoustic Guitar

Proper intonation ensures your acoustic guitar plays in tune across the entire fretboard, not just when the strings are open. Unlike electric guitars with individually adjustable saddles, acoustic guitars require more manual work, typically involving filing and shaping the saddle.

Why Acoustic Intonation is More Complicated than Electric

Most acoustic guitars have a single-piece saddle made of bone, plastic, or synthetic material seated in the bridge at an angle, rather than individually adjustable saddles like electric guitars. The saddle is angled to compensate for string thickness differences—lower strings need to be longer than higher strings. Many acoustic saddles also feature compensation points, particularly for the B string, which naturally requires different positioning for proper intonation.

Tools You’ll Want On The Bench

A precise tuner, saddle files, fine sandpaper (around 220–440 grit) for finishing, a sharp pencil for marks, and a small ruler or calipers. Fresh acoustic strings are non-negotiable.

Note: Be sure not to use Wetordry sandpaper, as it will discolor the bone.

Diagnose Before You File

Install fresh strings, set relief and action, and tune to pitch.
Check intonation at the 12th fret (and optionally 5th and 7th) using the open or harmonic as reference.
Note which strings are sharp (need to be longer) or flat (need to be shorter). Some techs compare the fretted 12th to the harmonic to better account for the act of fretting.
Mark where the contact point should move (consensus about where the contact point should be is about .005" per cent):

Fretted 12th sharp → mark back (away from the soundhole).
Fretted 12th flat → mark forward (toward the soundhole).

Adjusting The Saddle (Go Slow)

De-string and remove the saddle.
File carefully to relocate the string’s contact point. Tiny changes go a long way; you can always remove more, but you can’t put it back.
Reinstall, re-string, re-tune, re-check. Repeat in small steps until it locks in.

Advanced Considerations

Nut height that’s too tall makes first-position notes go sharp - set the nut slot heights with nut slotting files before chasing the saddle.
If the guitar needs extreme compensation or the saddle slot is poorly located, consider a pre-compensated or custom saddle, or consult a pro for saddle-slot relocation.
Remember: perfect intonation everywhere on a fretted acoustic is theoretically impossible; the goal is musically transparent across the board.

Ongoing Maintenance

Seasonal humidity and temperature changes move wood and tension. Check your intonation periodically, especially after string-gauge changes or setup tweaks. Old strings are the enemy of stable intonation.

Quick Reference: Reading The 12th-Fret Test

In tune: Open (or harmonic) and fretted 12th match—done.
Fretted 12th sharp: Lengthen the string (electric: saddle back; acoustic: contact point back).
Fretted 12th flat: Shorten the string (electric: saddle forward; acoustic: contact point forward).

StewMac Shop Notes

Make intonation the final step of your setup sequence.
Re-tune after every micro-adjustment—there’s no shortcut here.
Protect hardware: if a screw fights you, back off string tension before turning to avoid stripped heads.
Keep a consistent touch when striking test notes for repeatable readings.

Whether you’re nudging a Strat saddle or carving a compensated acoustic saddle, the recipe is the same: fresh strings, solid setup, precise measurements, and small, reversible moves. Do that, and you’ll get the payoff—fuller chords, sweeter intervals, and solos that sit right on the money.

Finish Strong with StewMac: Tools, Parts, and Support to Keep You in Tune

If you’ve worked through these steps, you’re already hearing the payoff—clear octaves, sweeter chords, and leads that sit right on pitch. To keep it that way, we’ve got the bench-tested luthier tools and guidance pros rely on: precision tuners and setup tools, nut and saddle files for fine compensation, feeler gauges and rulers for repeatable results, and replacement saddles, nuts, and bridge hardware for both electric and acoustic builds. And if you hit a snag, our techs are here to help you troubleshoot the last 1–2 cents.

Video Transcription

Aaron Smiley: Intonation is an important part of making sure your guitar plays and sounds the way that you want it to. And it's the last step, or one of the last steps, of any great setup.

Now, to be clear, we are not talking about tuning, which is something that you do at the headstock. We're talking about adjusting the intonation which is something that you do by moving the saddles forward or backwards at the other end of the guitar.

Basically you can be in tune at the headstock, but you'll never be perfectly in tune if your intonation is off.

In this video, we are only talking about adjusting electric intonation. Acoustic intonation can be an entirely different monster. It's not always a quick screwdriver turn or a file stroke away from being right. Sometimes it can get really structural.

Step 1: Set up the guitar

Before we go perfecting our intonation. We need to dial in the rest of the setup first. Now that means adjusting your truss rod. So your neck is straight or with the relief that you like. Adjusting the height of the strings off the fretboard so you have the action that you like, and of course, making sure you're in tune at the headstock. If you make any setup adjustments after you're done intonating it can throw your intonation off making you have to start all over. Now that the rest of the setup is done. Let's check the intonation to see where we're at.

Step 2: Check your intonation

A lot of times you can hear if your intonation is off, especially when you're playing up on the higher frets, but the differences can be subtle. The way to check that is either to strike the open note of the string or the 12th harmonic, whichever you prefer. Then fret the 12th fret and strike with the same attack as before. Although there's an octave difference they're still going to be the same note.

For example, a high E string, you'll get another high E at the 12th, just an octave higher. And you're listening for the difference between the two. If those notes are both the same note, then we're okay the intonation is all right, so we don't need to make any adjustments.

But this string is pretty far off. I can hear it. The open note is a B, but as soon as we fret it, we can hear that it's pretty flat. Now, this string's pretty bad. So it's easy to hear, but when you're making intonation adjustments, you always want to use a tuner.

Step 3: Adjust intonation

A lot of professionals like to use strobe tuners, because they're so accurate and we're doing some really fine adjustments here. But if you don't have a strobe tuner, you can always use a headstock tuner and that'll get you pretty close.

It's always a good idea to check the intonation in the playing position, partly because you're used to playing in that position, but also because gravity has a lot more of an effect on a setup then you might think. This tuner is confirming what we've heard. This string is flat, or the pitch is too low. To fix that we need to adjust the saddle towards the nut, which is going to shorten the string length and increase the pitch. If we are in the other situation and the string was too sharp, we would need to do the opposite. Move the saddle away from the nut, which lengthens the string and lowers the pitch.

A lot of times a screwdriver is all you need to make adjustments. Like on this Tune-O-Matic style bridge, for example. But you might not have a Tune-O-Matic style bridge and you might need a little bit of a different approach. This Hard Tail Bridge with six saddles also adjusts with a screwdriver, but this Floyd Rose needs an Allen wrench to change the location of the saddles. You might even have an archtop guitar that has a Floating Bridge that you need to physically move back and forth to change the length of the saddles. No matter what you're doing, the concept is the same. We're changing the length of the string by moving the saddles forward or backward.

Step 4: Final tune

Making these adjustments will pull the string out of tune. So it's always important to retune the string at the headstock after you make an adjustment before you check it again. Once you have that string dialed in, just move on to the other strings, with the same technique and you are all set.

Adjusting your intonation is something that you're probably going to have to do again. It's not a one-time fix. You may have to readjust the intonation as the seasons change, or if you change your string gauge. I usually like to give my intonation a quick check every time I change my strings, it doesn't take too long. And I also keep an ear out whenever I'm playing my guitar for any sour notes.

Overall adjusting your intonation can seem kind of scary but it's a pretty simple concept. And if you have a tuner and the right tool for the job, you can really dial in your setup that much more.