Guitar String Action Height at the 12th fret for a 6-string electric guitar is typically 1.5mm at High 'E' rising to 2.0mm at Low 'E'. This is generally considered as providing good tone with medium finger strength required for playing. 

Our Guitar String Action Height Gauge allows the action to be quickly and precisely set to the above values without any requirement for additional measuring tools.

From the initial setting, the string height can be adjusted up or down to suit playing requirements as detailed further below. 

Final action on the instrument should be determined by the feel of the guitar and its tone. 

String Action Height Gauge | GMC Luthier Tools
Guitar Setup String Action Gauge matched to fretboard



The thickness of the gauge increases progressively across the width of the fretboard to allow for the increase in string diameters.


String Action @ 1st  String:   1.50mm 


String Action @ 6th  String:   2.00mm

Guitar Setup Tool - String Action Gauge

Simple to use!: Insert the gauge underneath the strings at the 12th fret and lower the bridge/saddles until the strings rest on the gauge.



Place the gauge underneath the strings at the 12th Fret. Lightly pluck/strum each string close to the bridge to minimise free vibration and lower the the saddles until the open notes are muted.


Test the instrument for a good while to assess playability.  (Fret condition, instrument quality, style of playing and sound will determine any final adjustments.)




To lower the action: Move the gauge to the 13th fret and re-adjust the saddles/bridge until the strings are muted again.


To raise the action: Move the gauge to the 11th fret and re-adjust the saddles/bridge until the notes are audible again.


It is possible to set a combination of these i.e: Plain/Treble strings set with lower action using the 13th/14th fret positions and Bass/Roundwound strings set with higher action using the 10th/11th fret positions. 


“The fact is that string action does not follow a circular arc but a very gentle spiral shape widening as the string gauge gets larger. A neat concept!, and you can slide it left or right to get the right action. I saw this and was like "wow"!”. K.M., USA.



After setting the string action, the gauge can be used to set the pick up heights.


Place the gauge on top of the pick up poles and adjust the pick up height until the strings contact the gauge with the last fret position fretted.

Guitar Setup - Setting Pickup Heights



Five guitar gauge options are available:




15"            *(Suitable for 14" to 17" radius)

20"            *(Suitable for 18" to 20" radius)

*See diagram below for clarification


The scale diagram compares the geometry of commonly used fingerboard radii and their theoretical differences at the edge of the fretboard.  The gauge options are indicated by the solid lines. The dashed lines indicate intermediate fingerboard radii that can be accommodated as specified above*. 

Q. "I'm interested in your String Action Gauge but have two guitars with 14" and 16" radii. I can't see these sizes on the menu and wondered if you have a gauge for each of these".

A. "Thank you for your message. The 15" gauge is designed for 14" to 17" radii and will be suitable for both of your guitars. There isn't an option for 14" or 16" as the difference in geometry is miniscule (the gauge options are rationalised for practicality). I hope this helps!".

Reply. "That's great!. Thank You.!"

Fretboard Radius Comparison Chart


Guitar Neck Relief Setup | GMC Luthier Tools

The Guitar String Action Gauge can also be used in conjunction with feeler gauges and a capo to set the neck relief.


Guitar Neck Relief Setup Kit comprises of:-

  • Guitar String Action Gauge

  • 0.25mm Feeler Strip

  • 0.15mm Feeler Strip

  • Capo





For best results, the following order of adjustment is recommended:

  1. Set Neck Relief.

  2. Set String Action.

  3. Set Pick Up Heights




There is no requirement with this system to use a straight edge. 


The procedure is based on depressing the string simultaneously at the 1st and last fret and measuring the relief at the 8th fret. The gauge enables this to be done in a manner that also leaves both hands free to make adjustments.




The neck should be slightly concave with a typical relief of 0.25mm from the top of the 8th fret to the underside of the strings for a 6-string Guitar. 


For fast light playing such as Jazz, the relief can be set lower to 0.15mm.


The amount of relief will ultimately be a matter of preference and how the instrument feels and sounds.


Fit the Capo at the 1st fret and ensure all strings are fretted.

How To Set The Neck Relief on Your Guitar | GMC Luthier Tools

Feed the String Action Gauge through the strings below the last fret as shown in the following photo.

Guitar Neck Relief Setup | GMC Luthier Tools

Note 1st, 2nd, 4th & 5th strings pass over the gauge & the 3rd string runs underneath the gauge. The effect of this will cause the 3rd string to be fretted.


The string pressure and gauge curvature will ensure that fret contact is maintained and both hands are entirely free for truss rod adjustments and measuring.


Ensure the 3rd string is in contact with the last fret.


At this point if the current action is set high, and the 3rd string is not in contact with the fret, then the bridge should be lowered slightly until the 3rd string is fretted.



Position the feeler strip underneath the 3rd string between the 7th & 9th frets.

Guitar Neck Relief Amount | GMC Luthier Tools

The truss should now be adjusted until the string rests gently on the feeler strip.


With the feeler in position as shown the relief can be clearly seen to increase or decrease when the truss rod is adjusted. Both hands are also free to make the adjustments.


The advantages to this are:-

  • Instant confirmation that the truss rod is working correctly.

  • Indication that the truss rod is being adjusted in the right direction.

  • The truss rod needs only to be adjusted once until the string contacts the feeler.

  • There is less likelihood of damage and wear to the truss rod end and the headstock which can occur from excessive adjustments.

  • The instrument can be adjusted in a comfortable position.

  • User confidence that the relief has been set correctly.

The string action should now be set as per separate instructions above.