How to Set Guitar Action — String Height, Truss Rod, and Intonation Guide
Guitar action — the height of the strings above the frets — affects every aspect of playability and tone. Action that is too high makes the guitar physically difficult to play and causes notes to go sharp when fretted. Action that is too low causes fret buzz that muddy notes and can make some strings unplayable.
The correct action is the lowest possible setting that allows clean, buzz-free notes across the full length of the neck.
What You Need
- A ruler or string action gauge (in imperial or metric)
- A set of Allen keys (hex wrenches) — usually included with the guitar
- A Phillips screwdriver (for some bridge types)
- A capo
- An electronic tuner
- A feeler gauge set (for precise truss rod measurement — optional but useful)
Total cost: £10–20 for a basic action gauge and feeler gauge set.
Understanding the Three Adjustment Points
Guitar action is set by three separate adjustments, each affecting different parts of the neck:
1. Truss rod: A metal rod running inside the neck. Adjusting the truss rod changes the curvature (relief) of the neck. More relief lowers the strings at the nut end of the neck; less relief raises them. The truss rod does not directly set action at the 12th fret — it sets the neck curve.
2. Bridge saddles: Individual saddle heights at the bridge control the action at the 12th fret. Raising saddles raises action; lowering saddles lowers it.
3. Nut: The slots in the nut at the headstock end determine the string height in the first few frets. Nut slot adjustment requires a nut file and is a more specialised task — usually best left to a technician unless you have experience.
For most action adjustments, you only need to adjust the truss rod and bridge saddles.
Step 1: Measure the Current Action
Tune the guitar to pitch. Action is always measured in tune.
Place a ruler or action gauge at the 12th fret and measure the gap between the bottom of the string and the top of the 12th fret.
Standard electric guitar action measurements (at 12th fret):
| String | Low Action | Standard | Comfortable |
|---|---|---|---|
| Low E (bass) | 3/64" (1.2mm) | 4/64" (1.6mm) | 5/64" (2.0mm) |
| High E (treble) | 2/64" (0.8mm) | 3/64" (1.2mm) | 4/64" (1.6mm) |
Acoustic guitar standard action (at 12th fret):
- Low E: 6/64" (2.4mm)
- High E: 4/64" (1.6mm)
Acoustic guitars require higher action because the strings vibrate with more amplitude and require more clearance to avoid buzzing.
Low action (shred/lead players): Fret buzz is unacceptable for recording but manageable for live amplified playing. Some lead players set action as low as 2/64" on the treble side.
Higher action (acoustic, slide, blues): Slide guitar requires very high action — 6–8/64" on the bass side — so the slide does not contact the frets.
Step 2: Check Neck Relief
Before adjusting saddle heights, check that the neck has appropriate relief (bow).
Method: With the guitar in playing position, fret the low E string simultaneously at the 1st fret (or use a capo) and at the last fret. Look at the gap between the string and the 8th fret.
- Correct relief: A small gap — approximately 0.3–0.5mm. A thin business card should just pass through.
- Too much relief (neck bowed forward): Large gap at the 8th fret. Strings will be high in the middle of the neck.
- Back bow (neck curved backwards): No gap — string may be touching the fret. Causes buzzing in the lower positions.
Step 3: Truss Rod Adjustment
The truss rod is adjusted at either the headstock (most Fender-style guitars) or at the body end of the neck (most Gibson-style guitars). The adjustment is usually a 4mm or 5mm Allen key.
To add relief (increase bow, lower strings at nut end): Turn the truss rod anti-clockwise (loosening).
To reduce relief (straighten neck, raise strings at nut end): Turn the truss rod clockwise (tightening).
Critical rule: Turn in quarter-turn increments only. Tighten, then wait 24 hours before measuring again. The neck takes time to settle. Rapid, large adjustments can crack a neck or snap the truss rod.
If the truss rod feels tight or stuck: Stop immediately and take the guitar to a technician. A stuck truss rod is not a home repair.
Step 4: Set Bridge Saddle Height
Once the neck relief is correct, adjust the saddle heights to achieve the target action at the 12th fret.
Stratocaster / Telecaster (individual saddle screws): Each saddle has two small Allen screws on either side. Turning clockwise raises the saddle; anti-clockwise lowers it. Adjust both screws on each saddle equally to keep the saddle level.
Gibson Les Paul / SG (tune-o-matic bridge): The entire bridge is raised or lowered on two posts using a flat-head screwdriver or thumb wheels. Both sides can be set independently, allowing different bass and treble side heights.
Acoustic guitar (saddle): The acoustic saddle is a removable piece of bone or synthetic material in the bridge. To lower the action, the saddle is removed and material is sanded from the bottom. To raise it, a shim is added under the saddle. This is a more involved task than electric guitar adjustment.
After each adjustment: Retune and check action at the 12th fret. The string tension affects neck relief, so tuning is essential before measuring.
Step 5: Intonation
After setting action, check intonation — whether the guitar plays in tune at the 12th fret.
Method: Play the open string, then play the fretted 12th fret note. Compare with an electronic tuner.
- Sharp at the 12th fret: The string is too short. Move the saddle away from the nut (back towards the tailpiece).
- Flat at the 12th fret: The string is too long. Move the saddle toward the nut.
Adjust saddle position with the intonation screw at the back of the bridge (Stratocaster/Telecaster) or by adjusting the individual saddle positions on a tune-o-matic bridge. Each string requires independent intonation adjustment.
Retune after each saddle movement and recheck. Intonation affects every note you play above the open string — it is worth taking time to set correctly.
When to Take It to a Technician
Some adjustments are beyond the scope of DIY setup:
- Nut slot adjustment: Requires specialist files and risks cracking the nut if done incorrectly.
- Fret levelling: If you have high frets causing buzz in specific positions, a full fret level requires specialist tools.
- Stuck or very stiff truss rod: Do not force it.
- Acoustic saddle modification: Sanding the saddle requires care to keep it level.
A professional setup from a competent guitar technician costs £40–80 and includes all of the above. For a new guitar, a professional setup is often the best investment you can make — factory setups are rarely optimised for individual playing styles.
Recommended Action by Playing Style
| Style | Bass side (low E) | Treble side (high E) |
|---|---|---|
| Shred / Lead | 3/64" (1.2mm) | 2/64" (0.8mm) |
| Standard rock | 4/64" (1.6mm) | 3/64" (1.2mm) |
| Blues / Rhythm | 5/64" (2.0mm) | 4/64" (1.6mm) |
| Slide guitar | 8/64" (3.2mm) | 6/64" (2.4mm) |
| Acoustic | 6/64" (2.4mm) | 4/64" (1.6mm) |
Frequently Asked Questions
How often should I adjust my guitar's action? Guitars settle with seasonal humidity changes, string gauge changes, and age. Check action when you change string gauge, notice buzz that wasn't there before, or when the guitar has been in an unusually hot/cold/humid environment. Most stable guitars in consistent environments only need a setup once or twice per year.
Does lower action always sound better? Not necessarily. Very low action can reduce sustain and affect tone — the string vibrates with less amplitude and sits closer to the magnets on electric guitars. Most experienced players find an optimal action slightly above the minimum possible that allows clean notes. Extremely low action also makes bending less expressive.
Can I adjust the truss rod myself? Yes, if you proceed carefully — quarter-turn increments, 24-hour settling time, and stop if it feels tight. The truss rod is one of the most straightforward guitar adjustments. However, if you are uncertain, a professional setup is worth the cost of avoiding a mistake.
Why does my guitar go out of tune when I fret notes? Usually either high action or nut slot problems. High action causes the string to stretch slightly when fretted, sharpening the pitch. A nut slot that is too high has the same effect — notes played in the first three or four frets will be sharp. Check action at the 12th fret first, then have a technician check the nut if the problem persists.
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