Setup, done properly
Intonation.
How to get a guitar playing in tune all the way up the neck, why the nut decides more of this than the bridge does, and all the things that quietly wreck it while you are chasing your tail at the saddles.
The short version
Intonation means the guitar plays in tune everywhere, not just on the open strings. Tune it open, play a chord at the eighth fret, and if it sounds sour, your intonation is out.
The usual instruction is to compare the twelfth fret to the open string and move the saddle. That part is true, and it is maybe a third of the job. The other two thirds are everything that has to be right before you touch a saddle, and the nut, which nobody talks about and which quietly ruins more intonation jobs than anything else.
Pressing a string down onto a fret stretches it slightly, which raises its pitch. Intonation is the business of compensating for that stretch, and every single thing that changes how far the string has to travel to reach the fret changes how much compensation you need.
Get the order right, or you will do it twice
Intonation is the last step of a setup, not the first, because almost everything else changes it. Do these in this order:
- Strings on, the exact set you intend to use, stretched and settled. New strings drift for the first hour or so.
- Neck relief, set with the truss rod.
- Nut slot height, checked and corrected. This is the step people skip.
- Action, at the bridge.
- Pickup height, since magnets pull on strings.
- Then intonation, at the saddles.
Set the intonation first and then lower the action, and you have just changed how far every string travels to the fret, so your compensation is now wrong and you get to do it again. Change string gauge later, same thing. That is why luthiers get slightly weary when somebody says they only need the intonation done.
The nut, and why it matters more than you think
This is the part that gets left out of nearly every guide, and it is the reason plenty of guitars can never be intonated properly no matter how carefully you set the saddles.
If the nut slots are cut too high, the string sits further above the first few frets than it should. To fret a note down there you have to push the string further, which stretches it more, which pushes the pitch up. So the first few frets play sharp, and they play sharper the harder you press.
Now watch what happens when somebody tries to fix that at the bridge. They notice the low frets are sharp, so they lengthen the string at the saddle to flatten things out. That does flatten the low frets a little, but it also flattens everything else, so now the middle and upper neck are flat while the first position is merely less sharp. The guitar is worse everywhere and the person is baffled.
You cannot fix a nut problem at the bridge. The saddle compensates for stretch across the whole string length. The nut affects one end of the neck disproportionately. They are different problems and they need different fixes.
How to check nut slot height
Two checks, and the second is the one I trust.
The gap check. Fret the string at the third fret and look at the gap between the bottom of the string and the top of the first fret. You want that gap to be barely there, just visible, a whisker. If there is obvious daylight, the slot is too high. If the string is sitting on the first fret, the slot is too low.
The tap check. Same fretted position at the third fret, then tap the string down onto the first fret with your other hand. You should hear a very faint click. A loud click and obvious travel means the slot is high. No movement at all means it is too low.
The proof it is the nut and not the saddle
Here is the test that settles it. Compare the open string to the note at the twelfth fret, and then compare the note at the first fret to the note at the thirteenth fret.
Those two comparisons are both octaves, so both should be clean. If the twelfth against open is fine but the thirteenth against the first is sour, the problem is at the nut end, not at the bridge. That is because fretting at the first fret involves the nut height, and fretting at the thirteenth does not.
Another quick sanity check: play the first few frets and watch the tuner. If everything reads progressively sharper the closer you get to the nut, and it gets worse when you press harder, that is a high nut every time.
Fixing it
Slots get lowered with nut files sized to each string gauge, and this is slow, careful work. Take a little, check, take a little more.
Cut a slot too deep and the open string buzzes against the first fret, and now the fix is filling the slot or replacing the nut. Aim for barely visible clearance and stop. It is far better to leave a slot a hair high and check again than to take one pass too many.
Also cut the slot with the same downward angle as the headstock, so the string breaks cleanly over the front edge of the nut and rests on that edge, not on the back of the slot.
If the slots are too low and the open strings buzz, that is a new nut, or a fill. Filling with superglue and bone dust works and is a legitimate repair, though on a good instrument a new nut is the honest answer.
Now the saddles
With the setup done and the nut right, this part is straightforward.
- Tune the string accurately, open. Use a decent tuner and go one string at a time.
- Play the note fretted at the twelfth fret, with a normal touch, and read it.
- Compare it to the open string. The fretted twelfth should be exactly one octave above the open string.
- If the fretted note is sharp, the string is too short. Move the saddle back, away from the neck, to lengthen it.
- If the fretted note is flat, the string is too long. Move the saddle forward, toward the neck, to shorten it.
- Retune the open string and check again. Moving a saddle changes the tension, so the open pitch moves too. This is why it takes a few passes.
- Repeat until the open string and the fretted twelfth agree, then do the next string.
Sharp, go back. Flat, come forward. Sharp means the string needs to be longer, and longer means the saddle moves away from the neck.
| What you see at the 12th | What it means | What to do |
|---|---|---|
| Fretted note reads sharp | String is too short | Move saddle back, away from the neck |
| Fretted note reads flat | String is too long | Move saddle forward, toward the neck |
| Fretted note matches open | That string is done | Move to the next string |
Use the harmonic, or not
You will see the twelfth fret harmonic recommended as the reference instead of the open string. The harmonic is a genuinely accurate reading of the string's natural halfway point, and it works. But the open string is what you actually tune to and what the guitar has to agree with, so that is what I compare against. Either reference will get you there. Just do not mix them up mid job.
Check it where the music happens
The twelfth fret is the standard reference because it is the exact halfway point, but nobody plays only at the twelfth fret. Once the twelfth is right, go play. Check a few chords in first position, something around the fifth and seventh frets, and something up high. If a chord in a spot you use a lot sounds sour, you are allowed to split the difference and favour the region where you actually live. That is a legitimate choice, not a compromise of principle.
Do it under playing conditions
All of this only holds if you check it the way the guitar gets played.
- Guitar in playing position, not flat on its back. Gravity changes the neck slightly, and on some guitars it is enough to see.
- Fret with your normal touch. Mash the string and you will read sharp, and then set the intonation to compensate for a pressure you do not actually use.
- Do not bend the string sideways while fretting. Very easy to do without noticing, and it reads sharp.
- Let the note settle before reading. The attack of a plucked note is momentarily sharp as the string swings widest.
- Pluck with a normal attack. Hit it hard and the pitch starts sharp and falls as it decays.
Everything else that quietly ruins your intonation
String age
Old strings go false. Corrosion and uneven wear mean the mass is no longer even along the length, and a string with uneven mass cannot vibrate at a consistent pitch. You can set the intonation perfectly on a dead set and it will still sound wrong. Fresh strings first, always, and let them settle before you start.
String gauge and brand
Change gauge and you change tension, which changes how much the string stretches when you fret it, which changes the compensation you need. Different brands at the same gauge use different core to wrap ratios, so even that can shift things slightly. If you switch string sets, expect to redo the intonation. This is the main reason a guitar that was set up perfectly comes back needing work.
Fret height, wear and levelling
Tall frets need a lighter touch, because pressing hard on a tall fret pushes the note sharp. Worn frets with divots let the string sit slightly lower and the contact point moves, so the note goes off. And if the frets are not level, some notes are sharp and some are flat and no saddle position fixes it, because the problem is per fret, not per string.
This is also why a proper fret levelling job improves intonation across the whole neck without anyone touching the bridge.
Pickup height
Magnets pull on steel strings. Set a pickup too close and the magnetic pull fights the string's vibration, which can pull the pitch and kill sustain, most noticeably on the lower strings and up in the higher positions. If your intonation reads strangely and everything else checks out, drop the pickups a little and read again.
Tremolo systems
On a floating bridge, every saddle you move changes the total string tension, which tilts the whole bridge slightly, which changes every other string. So it is iterative, and it takes several passes back and forth before everything agrees. Get the bridge sitting level at pitch first, then intonate, then check the level again.
Neck relief
Relief is the slight forward bow in the neck. More relief means the strings sit further from the middle frets, which means more stretch to fret them there, which means those notes read sharp. Relief and intonation are tangled together, which is exactly why relief gets set first and left alone.
Why perfect intonation does not exist
Worth knowing so you stop chasing something unobtainable.
Frets are placed for equal temperament, which divides the octave into twelve mathematically even steps. That system is a compromise by design. It lets you play in any key on the same instrument, and in exchange no interval except the octave is perfectly pure. So certain chord shapes will always sound a touch off, and that is the tuning system, not your saddle.
On top of that, a guitar has six strings of different thicknesses and tensions, all being pressed by human fingers with varying pressure onto frets of finite height. There is no saddle position that makes all of that mathematically exact everywhere.
It means the guitar sounds in tune to your ear in the places you actually play, with your strings, your touch, and your setup. That is an achievable and genuinely satisfying result. Chasing an absolute number on a tuner past that point is chasing something the instrument cannot give you.
Quick troubleshooting
| Symptom | Most likely cause |
|---|---|
| First few frets play sharp, worse when you press hard | Nut slots cut too high |
| Open strings buzz on the first fret | Nut slots cut too low |
| Twelfth fret is fine but chords up the neck sound sour | Frets not level, or worn frets |
| Was perfect, now it is not, nothing was adjusted | New string set, different gauge or brand, or the strings have gone dead |
| Cannot get one string right no matter what | False string, or the saddle is at the end of its travel |
| Saddle has run out of adjustment room | Bridge placed slightly wrong at build, see the design stage |
| Readings jump around and will not settle | Reading the attack instead of the settled note, or a floating bridge still moving |
| Everything reads sharp the harder you play | Normal physics. Set it with your normal touch. |
If you are building
Everything above is easier if the bridge went in the right place to begin with. When you place a bridge, set the saddles to the middle of their travel and locate from there, and give yourself a little extra room past the calculated scale length, because the low E always wants to travel furthest back. Do that and every intonation job on that guitar for the rest of its life has room to work.
There is more on that in the design and templates guide, and on the fretwork that underpins all of this in the neck and fretwork guide.