How to adjust acoustic guitar intonation

The first step to correcting your instrument’s intonation is to address any issues that can cause intonation problems. If you haven’t done so already take a look at my list, most new intonation problems will be caused by one of these issues. Knowing the cause is the first step to fixing the problem.

Check Your Intonation

To check your guitar’s intonation you will need a tuner preferably, a chromatic tuner. Tune your instrument to pitch and fret each string naturally at the 12th fret. This note is one octave higher than the open string note and should be in tune (neither flat nor sharp.)

If notes played at the 12th fret are dramatically sharp or flat, changes to the strings length and position of the saddle (or shape of it’s crown) may be necessary.

When correcting poor intonation on an acoustic guitar I use an electronic tuner to evaluate the strings tuning at the 12th fret. I record this information for reference while making adjustments.

Only after any issues that can contribute to poor intonation are corrected do I may further adjustments to the nut and/or saddle.

Installing A Compensated Saddle

Installing a pre-made drop in compensated saddle is usually a simple upgrade. If your instrument has already been set up properly you can use your original saddle as a reference when sanding the height of the new one. If the instrument has any playability issues a set up should be performed along with the saddle upgrade.

Graph-Tech®, makers of Tusq® brand saddles, provide a large selection of pre-made compensated saddles. See assortment in right sidebar.

When pre-made saddles are not available thru retailers or from the original manufacturer the saddle must be made from scratch. In these instances a saddle blank is used and shaped to fit.

How to adjust acoustic guitar intonation
Dark lines show the peak of the saddle and the strings contact point. Compensated saddles allow us
to alter the individual string length and adjust intonation.

For instruments in need of extra fine tuning the shape of the compensated crown may need to be filed by hand, adjusting the length for each string individually. This is a more costly, time consuming method which may be required when good intonation can not be achieved using a pre-made saddle.

Installing Compensated Nuts

How to adjust acoustic guitar intonation
Compensated nut

Fretting a string stretches it and stretching a string will sharpen it slightly. To offset this sharpening, length is added to the instrument’s scale length to compensate.

However, lengthening the string to compensate for fretted notes also lengthens the open string.

Compensation of the nut can be achieved in different ways. Most have settled on a "shelf system" whereby the nut overhangs the end of the fingerboard which renders it slightly shorter. This eliminates the need to permanently modify the fingerboard’s length by cutting it.

Earvana® is one example of a prefabricated compensated nut.

The Buzz Feiten Tuning system® is another method. Modifications are made to the position of the nut or fingerboard length. Intonation is then adjusted according to slightly offset tunings which are determined by string gauge, scale length and action.

My advice is to try the self-nut first, before modifying the fingerboard’s length. I find it difficult to justify shortening the fingerboard of a vintage or valuable instrument.

Using Tuning Techniques

Just as there are several theories about ideal saddle and nut compensation, there are also different ways which we can tune our instrument.

One of the most popular methods is to use a chromatic instrument tuner to tune the open (un-fretted) strings. Other methods include using harmonics to tune or tuning 2 particular chords until they are in tune with one another. You can use whatever method you feel pleases your ear.

Correcting Saddle Location

Some instruments suffer from poor intonation because the bridge and/or it’s saddle slot is not located properly. It is either too close to the fingerboard causing sharp intonation, or too far, causing flat intonation.

How to adjust acoustic guitar intonation

This instrument played terribly sharp due to a misplaced bridge.
The yellow arrow reveals the correct location for saddle placement.

When possible (and appropriate), the original slot is filled and re-routed to correct the problem.

How to adjust acoustic guitar intonation

Ebony was used to fill the original saddle slot prior to reslotting.
When the correct placement is not possible a new bridge is made
to avoid placing the saddle too close to the bridge pins.

How to adjust acoustic guitar intonation

A bridge slotting jig serves as a guide for my laminate trimmer.

Bridge Replacement

On the bridge below, moving the saddle’s position would have placed it too close to the bridge pin holes. Instead a new bridge was made.

It is quite common to see this scenario on Martin guitars built in the 70’s (though they are not the only example).

How to adjust acoustic guitar intonation
Note the positions of the bridge pin holes and saddle slot.
The top bridge is an original, the bottom is the replacement.
Also of note is the proximity of pickguard to bridge.

Physically moving an acoustic guitar bridge to correct the intonation would leave behind a nasty unfinished area on the top which would be easily noticeable even with touch up. The alterations I make allow the bridge to sit on the same "footprint" and are only noticeable to those well acquainted with the original design.

In Search Of Perfect Intonation

Having every single note in perfect tune is beyond the abilities of many equal tempered instruments. There are in fact compromises and for a select few . they may always be disappointed with the intonation of a fretted instrument.

How to adjust acoustic guitar intonation

If you play guitar, you’ve probably heard the term “intonation.” It’s often used in the context of talking about a guitar’s setup. A setup is a way of fine-tuning the relationship of the guitar’s components, such as the guitar strings, bridge, nut, saddle, neck angle, and with electric guitars, pickups, all to optimize the guitar’s feel and sound. (Think of a tuneup for a car or bicycle.) Guitar makers set up their instruments according to their own specifications, and any guitar service technician can easily handle either a basic setup or a more customized setup to suit a seasoned player’s preferences and playing technique.

What is intonation?

With musical instruments, intonation refers to pitch accuracy—the extent to which the notes formed are in tune, versus being flat or sharp. When a player tunes a guitar using an electronic guitar tuner, they do so by plucking the open (unfretted) strings. However, when a string is fretted, the tension on the string increases, which bends the pitch of the note slightly upward. The effect is subtle, but this change can impact the intonation, in some cases causing “sour” notes and dissonant chords if the guitar’s intonation is not set properly. Often intonation issues are associated with playing higher up the fretboard (closer to the guitar body).

Something else to keep in mind is that the closer a string is to the frets, the less it needs to stretch since it doesn’t have as far to go. This means that low action tends to produce more accurate intonation. Intonation issues can be subtle or dramatic depending on a guitar’s setup. For guitarists who record or play music live, intonation problems can ruin a recording session or a live performance.

How is acoustic guitar intonation adjusted?

While adjusting the acoustic guitar intonation is conceptually the same as an electric guitar, due to certain differences in construction (e.g., different types of saddles) the processes vary in some respects. Most acoustic players take their guitars to a qualified guitar technician when they need their intonation adjusted.

Typically, proper acoustic guitar intonation begins with a full setup, along with a fresh set of strings. With Taylor guitars, provided there is no fret wear, the setup often solves serious acoustic guitar intonation problems. However, many high-level players still appreciate a luthier’s specific attention to intonation, because it will address each player’s style and technique on that particular instrument. The technician will check the guitar’s action (the distance between the strings and the fretboard), as well as the instrument’s neck relief. This refers to the slight bowing intentionally created in the neck to set the action. It can be controlled by tightening or loosening the truss rod, which is located in the neck. Essentially, the technician is trying to get everything right before actually adjusting the acoustic guitar’s intonation. This removes the extra variables and makes it easier to dial in the intonation.

From there, they’ll usually address the nut and saddle, where the strings stretch over a piece of bone, plastic or other synthetic material. Most saddles are placed at a slight angle to the bridge, which adds length to the lower strings to adjust for differences in string thickness. Likewise, many saddles are made with compensation points for some or all of the strings, which helps fine-tune those points even more. When addressing a player’s particular style and technique, a skilled guitar technician can cut more accurate notches into the saddle, effectively adjusting the intonation of each string by changing the string’s distance from the nut. The technician will check the pitch of each string at the 12th fret to ensure that it’s in tune with the pitch of the open string.

Checking the nut, where the strings rest at the peghead before winding around the tuning machines, is critical. String slots that are cut flat, high-centered, or left too high, along with improper placement of the nut, will prevent a guitar from achieving good intonation. At Taylor, we have the added benefit of our proprietary neck design, which ensures that every guitar is built with proper action and accurate nut and saddle location. The guitar neck design also makes it easy to adjust the neck angle and allows for setup-related intonation fixes without changing the position of the nut or the saddle.

In the end, intonation on a tempered scale instrument can never be perfect. And keep in mind that another factor that can affect acoustic guitar intonation is a person’s playing technique. For example, players with a heavy fretting hand or a beginner might press down harder than necessary on the strings, resulting in notes going sharp. In other words, in a certain player’s hands, even a properly set-up guitar can sound like it’s out of tune. Since there are so many variables, we recommend that players change their strings before consulting a service technician to adjust their intonation, since guitar strings naturally lose some elasticity with time and wear. Otherwise, a technician can find the sweet spot on your guitar that provides the best possible intonation all the way up and down the neck.

If you have questions about intonating your guitar, check with an authorized Taylor service technician or call our Customer Service department.

How New V-Class Bracing Improves Intonation

In early 2018, Taylor released a new internal bracing system called V-Class, which dramatically revoices the top of an acoustic guitar. The V-Class design breaks away from the tradition of X-bracing, which for decades has served as the standard voicing architecture inside most steel-string acoustic guitars. The V-Class pattern fundamentally changes the way the top responds to the strings, increasing the stiffness along the center of the guitar (in the direction of the strings) to enhance the sustain, while also creating more flexibility across either side of the lower portion of the top to enhance the volume. But the design accomplishes another impressive feat: It largely resolves an acoustic guitar’s natural intonation imperfections. What makes this noteworthy is that bracing normally isn’t even associated with intonation; usually intonation issues are addressed along the fretboard, through the guitar’s setup and compensation. But as it turns out, the top movement also plays an important role in the intonation.

X-bracing, by virtue of its design, creates disorderly zones of vibration in the top that cause clashing sound waves (think of choppy sea conditions). Basically the vibrating top isn’t completely in sync with the vibrating strings. We experience that chaos as dissonance, the beating or wavering sound that occurs when you play a chord voicing that the acoustic guitar isn’t built to reproduce accurately.

V-Class bracing resolves that chaos by creating a more orderly response from the top, which vibrates in more of a side-to-side rocking fashion. Essentially the top is now more in tune with the strings. Without those clashing waves, those slightly dissonant chords sound clearer with more harmonic agreement, and without the sourness that can be heard with certain voicings.

How to adjust acoustic guitar intonation

Over the next little while I’ll give you some information on how to assess and set the action on a number of guitars and basses. If every, single instrument isn’t covered, there should be something that’s similar enough to an instrument like yours, or—at least—enough information to figure out how to approach your own.

Before we begin, you should remember that intonation is the last thing you will do when setting up your guitar or bass. If the nut, action, relief and pickup height is not where you want it, there’s no point setting intonation (and it’ll be more difficult). Get everything else right first and then look at intonation.

There are a few things going on here but for the most part, think of it this way:

When you fret a note on a guitar (or bass—let’s assume we’re talking about either instrument for the rest of this article), you actually stretch the string a little. This stretching sharpens the note by just a little.

To compensate for this—and you’ll often hear intonation referred to as ‘compensation’—we make each string a little longer, effectively flattening it.

Heavier strings will need more compensation than lighter strings. This is why you can see an acoustic guitar saddle angles back as it goes from treble to bass strings.

How to adjust acoustic guitar intonation

String compensation. Saddle on acoustic guitar angles to allow bigger strings more compensation

On most electric instruments, you’ll likely have adjustable saddles to easily compensate each string. Some guitars are more or less flexible in this regard (and we’ll get to individual instruments in a little while) and acoustic instruments with non-adjustable saddles present more of a challenge.

Before we start, remember the prerequisites: The rest of your setup must be right for you and you should have fresh strings installed, properly stretched, and tuned up as normal.

Also, you’ll always check with the instrument in the ‘playing position’, not resting on its back on a bench or similar. The instrument should be orientated as if you were playing it. Ideally, sit comfortably and hold the instrument in your lap like you would if you were playing. Feel free to set it down on a bench or whatever to actually make the adjustments but always back to playing position to check.

The basic theory is this:

Pick the open string and verify it’s in tune.

Fret at the 12th fret and pick this note. Compare it to the pen string—is it flat or sharp?

So you just bought a new guitar, and you pull it out of the box and tune it up. Why do all the chords sound…wrong? The answer is probably your intonation, and it is easy to do at home! Today we will talk about the easiest way to intonate your guitar at home.

How to adjust acoustic guitar intonation

Intonation Adjustment.

How Do I Set My Intonation: Wait… What Is Intonation?

Most guitars come setup and ready to play out of the box these days. But that doesn’t mean a few mistakes can’t slip by quality control. In fact, intonation is probably the #1 problem a new guitar may have.

Have you ever played an open chord and it seems like just one string is slightly out of tune? Of course, you check your tuning again with a tuner. All the strings are in tune! What in the heck is wrong?

So maybe your intonation is off. It seems devastating at first, especially with a new guitar. But it is an easy fix, with just a tuner, some patience, and a screwdriver.

So what is intonation?

Intonation is how in-tune your guitar is along the entire fretboard. A guitar with a setup intonation will be in tune everywhere on the fretboard. A guitar with bad intonation will be out of tune in some areas of the fretboard.

Intonation is the length of your strings at the bridge. Look at it as “fine tuning”. There are screws at the end of your bridge that you can tighten or loosen depending on your intonation situation.

This is why one note in a chord may sound off. That one string may be a little too sharp/flat when you fret the note.

There are many schools of thought when it comes to setting your intonation, but I have the easiest method in my opinion. We can go through it step by step.

Setting Your Intonation: Tools

  • Screwdriver
  • Electronic tuner
  • New Strings
  • Patience!

New strings are an optional thing. But I feel like I get the most accurate reading with freshly stretched, new strings. Check the screws on your bridge, and see if they are Philips or Flathead, and find the appropriate screwdriver. Otherwise, you’ll need a good tuner.

No matter what kind of bridge you have, the process is the same. Whether it is a Stratocaster or a Les Paul style bridge, all you are doing is adjusting the string length by tiny increments!

How Do I Set My Intonation: The 3 Step Process

There are a lot of ways to go about this, but today we are looking at the easy way. This is the easiest way to learn the process, but you may want to try a different way, later. But you will at least understand what you’re doing by learning this method, first

We can break this all down to just three easy steps. It may sound complicated at first, but it you’ll get it after a couple of tries. Not to mention, you cannot permanently ruin your guitar or anything by trying this yourself.

Step 1: Check your tuning: Tune up your guitar like you normally would. Nothing complicated here! Just tune your open strings.

Step 2: Checking the intonation: Now that your guitar is tuned, go to the 12th fret. The 12th fret will be the same note as your open string, as it is the octave note. Fret the note on the 12th fret, what does your tuner say?

If it is the low E string, it should say E and match the tuning of the open string. If it doesn’t? Your intonation is off.

How to adjust acoustic guitar intonation

This process will be the same no matter which string you are working on. So how do we fix it? Checking the note at the 12th fret

If The Note Is Flat…

How to adjust acoustic guitar intonation

The note is flat on the 12th fret

If you have a flat note when you strum the string while fretting the 12th fret, your intonation is off. If the note is flat, you need to adjust the string saddle towards the neck. This will lessen the length of the string.

  • Tune the string open
  • Check the 12th fret’s tuning
  • Adjust the bridge saddle
  • Recheck tuning

Ideally you want the pitch to read the same open as the 12th fret. Or at least get it as close as possible.

How to adjust acoustic guitar intonation

If the note is sharp? The 12th fret is too sharp

If you find that the note on the 12th fret is too sharp, you will reverse the process! Instead of tightening the string and moving the saddle towards the bridge, you will move the saddle backwards.

Use the same method, checking your open tuning. Then checking the 12th fret again. Do this for each string. Once each string is in pitch, you’re done!

If you have very small set screws on your bridge, be very careful not to strip them! Take it easy when making adjustments, and only do a turn or so at a time.

Factors That Affect Your Intonation

  • Changing string brands
  • Changing string gauges
  • Climate
  • Old strings

Changing your string gauge will usually be the #1 culprit for wonky intonation. Thicker strings especially will offset your intonation across the whole guitar.

Extreme climate changes can also affect your intonation. Too much humidity, or little humidity can wreak havoc on a guitar, particularly the neck. If your guitar is in an unstable environment, it is a good idea to keep it in it’s case.

Old strings can also affect your intonation and tuning, if it they are old. At a certain point in a string’s life, they stretch or shrink. I like to stick to the 1 month rule, if you play pretty often.

How to adjust acoustic guitar intonation

Guitar intonation is, as the name implies, related to the tone of your guitar strings. You’ve probably noticed that certain strings sound off no matter how well you’ve tuned them.

Poor manufacturing usually causes bad guitar intonation. Or, it might be that you’ve simply used your ax so much that you’ve worn down parts of it.

What Causes Poor Guitar Intonation?

Manufacturers set up your guitar in a very specific way, and any flaw in the setup, however tiny, can have a massive impact on how your guitar sounds. Here are some common causes of poor intonation.

1. Faulty Guitar Strings

Not all guitar strings are created equal, and maybe you’ve bought a bad set. Eliminate this cause by changing the strings. You can do that quickly and easily with the Roadie 3.

2. Too High String Action

Sometimes, If you’ve set high action at the nut or bridge of the guitar, the strings have to bend further when you press them down towards the fret. Adjust your strings to a lower action to avoid this cause.

3. Extreme Guitar Neck Relief

Extreme neck relief is one of the causes of high action, which leads to poor intonation. Turn your guitar sideways to see if your guitar neck is straight dipped or over bent. If it’s not flat, then straighten the neck.

4. You Have Not Positioned your Intonation Pieces Properly

The strings rest on the intonation pieces that form part of the bridge. Improperly positioned intonation pieces can cause poor intonation. Adjust them individually for each string.

5. The Nut Is Worn Down or Not Set Properly

A worn down or improperly positioned nut can cause bad intonation. A worn-down nut will need replacement, and a nut set too high should be filed down in order to lower the string action.

6. You Have Not Positioned your Frets Properly

Each fret represents a half step on the chromatic scale and is positioned based on mathematical calculations. Check to see if you’ll need to re-fret the board.

7. The Frets Sit Too Loosely in the Slots

The frets can sit too loosely if you’ve dropped the guitar or they’re manufactured wrong. As with poorly positioned frets, the only solution to this problem is to re-fret the board.

How to adjust acoustic guitar intonation

8. The Nut and Frets Are Worn or Damaged

The friction of the strings can wear down the nuts and frets on your guitar. So, you may need to replace the nuts or replace the frets if either of these become worn down or damaged.

9. Switching String Gauges

Alternate tunings are great, but they sometimes require higher gauge strings which can increase tension and warp the guitar neck. Combat this by not switching string gauges too often.

Have you identified the problem?

Hopefully, the reason for your guitar’s poor intonation is one of these nine reasons we’ve listed above.

Stay tuned for our next article on How to Intonate a Guitar!

Know of any common causes of poor guitar intonation that we’ve missed? Drop us a comment in the section below and share your knowledge!

How to adjust acoustic guitar intonation

Time to break up all this Burlesque talk with something a little different. What’s going on here, then?

Intonation. It’s a bug-bear for some. We could talk about equal temperament concerns and mathematical subdivisions of scale-length and whatnot, but it would get dull quickly. Suffice it to say, tuning on any fretted instrument is always a little bit of a compromise.

In order to try get the damn thing to sound as closely in tune as possible, we ‘intonate’ each string to compensate its length so it sounds right when fretted. On most electric guitars, we do this by adjusting the string’s saddle—moving it backwards or forwards to slightly lengthen or shorten the string’s sounding length. Easy-peasy (unless it’s a Floyd Rose-type bridge in which case it’s more annoying than being repeatedly kicked in the shin by a crying child in a restaurant).

Acoustic guitars offer a bit more of a challenge than most electrics though.

An acoustic guitar generally has a fixed saddle (of bone or whatever). The fact that the saddle is installed at a slight angle (increasing string length from 1st to 6th) string is a nod towards some string compensation. The pre-shaped, compensated saddles that many guitars have these days is another step in the right direction.

For most people (and most guitars and strings) these get close enough that tuning issues aren’t glaringly awful.

Sometimes, and for some people (depending on playing style and the curse of having a good ear), it’s not enough.

How to adjust acoustic guitar intonation

How to adjust acoustic guitar intonation

Intonation depends on precisely seventeen million variables. Well, give or take—there are a lot of factors that all interact to determine the best setting. Tweaking setup and string choice can help if there are problems but sometimes that’s not an option or isn’t sufficient.

What’s going on in the images above is that I’ve used little chunks of rosewood to individually intonate each string on this acoustic guitar. The saddle has been removed and the rosewood is acting like an individual saddle for each string. I poke it back and forward to find where each string properly intonates.

StewMac actually offers a doohickey that does this without fiddling with bits of wood. I’ve been threatening to get one for a while but I’m forgetful and tight.

Popping a piece of cellophane over the bridge lets me mark the location of each intonation point and the actual saddle location itself. This gives me an indication of where each string should sit on the saddle to sound best. It’s easy to transfer this to a new saddle blank.

This guitar, its setup and strings, actually indicates a complication: As you can see in the image in the right, some of the optimum intonation points sit outside the actual saddle.

This happens sometimes. On an older guitar, it’s not unusual to have a saddle actually misplaced. This can necessitate filling the slot and actually re-routing it in a new position. That doesn’t tend to happen so much these days but, depending on other factors, it’s possible that one or more intonation points might be in front of, or behind, the saddle. Of course, making a much wider saddle is an option but that adds expense and entails modifying the bridge to accommodate that wider saddle.

How to adjust acoustic guitar intonation

The other option is compromise (we’re back to that word again). In this case, carving a new saddle with intonation points as close as possible to those measured will improve things considerably. Four of six strings will be pretty much perfect and the remaining two will be a lot closer to perfect than they originally were. Overall, it sounds much more in tune than it did without the need to irreversibly modify the bridge to accommodate a wide saddle.

So, we end up with a slightly odd looking saddle that sounds a lot better and the original is safe in the case in case it’s ever needed. Not too shabby.

It’s worth remembering that this is probably overkill for the majority of people. Most guitars and guitarists are generally ok with the regular or pre-compensated saddle. Failing that, a good setup or a change of string-gauge will probably get you close enough that you’ll be happy. If you’re still hearing problems though, a custom-compensated saddle might be an option.

Simply put, how does one adjust it. I have a low-end acoustic where the intonation seems to be out by quite a bit and I’d like to adjust it.

It comes down to adjusting string size or length, so I guess I’m looking for methods of adjusting these easily/accurately. The guitar has the usual plastic bridge insert.

3 Answers 3

There are a lot of things you can do. Generally, the first rule is change the strings. If the intonation is still out, then you will have to do a little more work.

At this point I would recommend taking the guitar to a specialist technician, particularly so if this is your first time setting up a guitar. Even though the guitar was cheap, you have a good chance of messing something up quite badly if you are a bit inexperienced with these sorts of things. Plus, the cost of the setup from the technician will probably bring the total amount spent on the guitar to what a decent low-end guitar would cost anyway.

During the setup, the technician is likely to:

  • Adjust the neck and bridge piece so that the action is lower
  • File the nut down to correct levels or replace it entirely
  • Check the bridge for damage/cracks that could cause bad intonation
  • Possibly replace the bridge piece entirely with a ‘compensated’ saddle.

Cheaper acoustic guitars are likely to have a ‘straight’ saddle, to keep production costs lower. ‘Straight’ saddles are not the best at providing good intonation on a guitar.

For details about what ‘straight’ and ‘compensated’ saddles are, I’ll borrow what I wrote in answer to this question:

Saddles also come in two different variants: straight and compensated. ‘Straight’ saddles are straight lines with a rounded top surface that the strings lie over. Compensated ones have recessed and prominent sections (particularly where the top B and E strings are) which aid the intonation, which can be hard to manage on an acoustic guitar.

My guitar does not play in tune, even after I know I’ve tuned it correctly. Some chords sound in tune while others don’t.

This article details the reasons a guitar will not play in tune. To view information about "staying" in tune, please refer to my article on tuning issues.

Checking Intonation

To check intonation you will need an electronic tuner. Tune your instrument to pitch and fret each string naturally at the 12th fret.

If notes played at the 12th fret are dramatically sharp or flat, the intonation may require correction.

Things That Can Cause Poor Intonation

  • Physical placement of saddle (this determines the string’s length)
  • Wear on the string’s contact points (frets, nut, saddle)
  • Very tall frets (too much distance between the fret and string)
  • Playing technique

High Action

Very high action (string height) causes a string to be stretched as it is fretted. In the same way that bending a string causes the note to become sharp, pressing a string down when the action is quite high will also cause string stretch.

When string height at the nut is too high, chords and notes in the first position are often out of tune.

Correction: The instrument should be properly set up.

Excessive Neck Relief

A neck with far too much relief (bowing in the neck) not only shortens the distance between the nut and saddle, it raises the string’s distance from the frets.

Correction: Adjust the truss rod to obtain proper neck relief and set up if necessary.

Leaning Saddle

The saddle should sit firmly in the bridge. A loose saddle can lean forward, shortening the string’s length and sharpening the intonation.

Correction: Replace the saddle for proper fit.

Worn Saddle Crown

Deep notches in the saddle may change the string’s length.

Correction: Replace or re-surface the saddle.

Fret Wear

Frets that are badly grooved or have flat crowns will also throw off intonation as the string’s length is changed.

Correction: Worn frets can be leveled and re-crowned to remove the grooves. Severely worn frets may require replacement.

Fret Height

Instruments with very tall fret wire can play incredibly sharp if the string is fretted hard.

Using an electronic tuner fret a note and watch the tuner as you apply more or less pressure to the string to view the effects.

Correction: If the fret crown is very tall, fret leveling and re-crowning can reduce it’s height.

String Quality & Gauge

String quality has really only been an issue for my clients when purchasing no name strings from auction sites. While seemingly cost effective some are notorious for bad intonation.

When re-stringing an instrument that has been properly set up it is important to use the same string gauge. Saddle compensation, neck relief and action have all been set for a particular string gauge. Increasing the tension of the strings can cause sharper intonation.

Correction: If the instrument played in tune before and no changes have been made to the instrument you may wish to change strings first.

Saddle Placement

The string is always resting in the nut’s slot and on the saddle’s crown. Changing the position of the saddle or nut will therefore change the length of the string.

A string that is too long will cause the intonation to be flat at the 12th fret.
A string that is too short will cause the intonation to be sharp at the 12th fret.

Correction: The saddle’s crown may need compensation or, in more severe cases, the bridge saddle slot may need to be moved.

Fret Spacing

I hate to mention this as I fear far too many people will jump to this conclusion in error, but I still encounter this on occasion. This is generally seen on inexpensive imported instruments and some vintage pieces with hand slotted fretboard’s.

Correction: Fingerboard replacement.

Playing Technique

Some players have a rather powerful fretting technique in which they place excessive pressure on the strings when fretting. If the instrument happens to have fairly tall frets the combination often results in sharp intonation.

To illustrate, use an electronic tuner and play a note using varying fretting pressure. The tuner will show you how your pressure effects the note.

A Word About Scale Length

Common Scale Lengths*

Martin Dreadnought 25.4"
Martin 000-28 24.9"
Taylor Grand Auditorium 25.5"
Gibson J-45 24.75"

*some editions may vary

When trying to determine the Scale Length on an instrument measure the fingerboard from it’s start (where it touches the nut) to the center of the 12th fret. Double this number to arrive at the Scale Length.

How to adjust acoustic guitar intonation

Scale Length can be determined by measuring from the
end of the fingerboard, to the center of the 12th fret and doubling it.

In order to compensate for the sharpening that occurs when fretting notes up the neck, additional string length is added to the scale length in order to provide better intonation.

If you look at the saddle on a steel string guitar you will quickly realize that they are not in a straight line (with the exception of some classical guitars). Saddles are slanted because string length is actually added to the instruments scale length in order to off set the sharpening of the note which occurs when the string is stretched while being fretted.

The larger the string, the more compensation is usually necessary, thus the bass side of the saddle will be further from the fingerboard than the treble side.

Now that the truss rod is adjusted, the string action at the bridge is adjusted, and nut slots are dialed in, you can now do the last step of the setup, which is to adjust intonation.

Tuning fretted instruments

Fretted instruments have equal temperament by design, and therefore have limitations when it comes to tuning. By this I mean that the tuning of each individual note is a function of the fret location on the fretboard. Fretless basses would be the exception to the rule, in that the player is intonating as they play. The same is true with stringed instruments like violins and cellos.

Since you are unable to move the actual frets, you have to make sure the instrument stays in tune up and down the entire span of frets by making adjustments at the bridge saddles.

The rule of thumb here is that a string, when struck at the 12 th fret, should produce a tone exactly one octave above the open note on the same string. If I play the open high E string, the 12th fret E an octave above it on the same string should also be in tune. Players all want the same thing, and that is a guitar that plays in tune and stays in tune. Good intonation is mandatory in making this happen.

Use a strobe tuner

Put the entire guitar up to pitch using a strobe tuner at the open notes. Then check to see if the strike note at the 12 th fret on each string is perfectly in tune with the open strings. If the 12 th fret note reads a little sharp on the strobe tuner, move the saddle back and away from the nut, therefore lengthening the string. Then retune the open string and check again until it’s perfect. If the 12 th fret note reads a little flat on the strobe tuner, move the saddle toward the nut, therefore shortening the length of the string. Then retune the open string and check again until it’s perfect.

On most guitars with separate saddles this will be an easy process. But it’s a little more difficult on bridges where two or three strings share the same saddle (such as barrel bridges on a Telecaster) or on acoustic guitars with a fixed bridge. On Telecaster bridges you will make adjustments until both strings are as close to in tune at the 12 th fret as possible. Sometimes you will not be able to perfectly intonate these guitars because of the limitations of the bridge saddle design. However, you can always recommend changing saddles to something that intonates a little better, such as angled saddles.

Limitations of wrap-tail bridges

On vintage wrap-tail bridges, you will also have limitations in the design. I have found that it is best to intonate the high and low E strings and then let the rest go as they are. Archtop guitars with a floating bridge design will be very similar to wrap-tails. You can physically move the bridge to the correct intonation point. Be sure to slack the strings before moving the bridge base over the top, as the downward string tension might scratch the finish. On acoustic guitars, you will have the most severe intonation adjustment limitations, as the bridge saddle slot is routed at the factory and you will not be able to move the bridge saddle to intonate.

In most cases, if the neck and nut slots are adjusted properly with a reasonable string action and good neck angle, then the guitar should play in tune up the neck. If the setup is good up to the intonation step, then it’s possible that you might have to cut a new saddle that will move the strings closer to proper intonation (like an acoustic saddle with a notched B string to compensate for the string gauges). If severely off, then you might have to fill and recut the saddle slot. Both of these examples would obviously be in the category of “repair” work and therefore beyond the scope of a simple setup.

Check your tuning job

After the intonation is set with a strobe tuner, check to make sure that the guitar is really intonated correctly by playing octaves in the upper register. I like to play octaves, skipping strings at the 12 th fret, just to hear if there is any “wobble” in the tuning or if something is not right (12 th fret low E and 14 th fret on D, for example). You always want to double-check your work and make sure that the guitar really does play in tune.