Most quality guitar manufacturers supply the correct tool for adjusting neck.
Measure neck relief guitar.
Fretting at the 13th fret means the string rests on the top of the 12th fret bob.
A guitar neck is typically not perfectly straight but has a dip about mid way this is relief.
With a straightedge placed between the d and g strings bow will become apparent.
Relief is the curvature of the neck.
A simple routine measurement you can perform yourself on your guitar or bass is the amount of neck relief which is the amount of curvature along the length of the neck.
Someone correct me if i m wrong but i believe you want to measure relief between the first fret and the fret at which the body of the guitar joins the neck.
Adjusting your guitar s neck relief the amount of bow and resistance in the neck may sound like a scary proposition to the first timer but this task is something you can definitely do yourself if you take it slow and work in very small increments.
A simple guide to finding out how to determine this important measurement that will keep your guitar sounding great.
I measure it by putting a capo on the 1 st fret holding down the string on the fret where the neck meets the body thus creating a straightedge with the string and measuring the gap between the bottom of the low e and the 7 th fret.
Hold down the 6th string at the last fret.
At the deepest point of the curve which is usually at about the 7th or 8th fret on an electric guitar this should measure between 0 005 to 0 020 inch or 0 015 to 0 05 centimeter.
The largest gap is usually towards the center of the neck.
The fretboard extension should not be included for the purpose of measuring or adjusting relief.
At that point you ll need to adjust the truss rod.
If you have two capos that s even better as you can keep both hands free.
Here is my process for measuring existing neck relief.
Place a capo on the first fret then use your finger to fret the e string uppermost string closest to where the neck deepens to join the body.
On a typical acoustic guitar that will be from the first fret to the fret at or just past the body joint.
If you use a straightedge longer than the neck you re no longer measuring relief.
Relief is calculated with the instrument tuned to pitch so we can measure the bow created by string tension.
Place a capo on top of the 1st fret fig.
How to measure neck relief on guitar or bass.
To measure relief clamp a capo on top of the 1st fret and then hold down the 6th string at the last fret.
To measure neck relief you ll need a feeler gauge and a capo.
So you would fret the string on fret 1 and fret 13 for a 12 fretter i think.