Relief and action are the two measurements that decide how a guitar feels, and they are routinely confused with each other. Relief is the slight forward curve built into the neck. Action is the height of the strings above the frets. They interact, which is why the order you adjust them in matters.
Set the action first and you will set it again after you adjust the relief. Set the relief first and the action adjustment is the last one you make.
Relief: what it is and why it exists
A vibrating string needs room. It swings widest at the middle of its length, so if the neck were perfectly straight the string would buzz against the frets around the seventh to ninth position. Relief is a small forward bow — typically 0.15 to 0.25 mm at the seventh fret — that gives the string room where it needs it.
The truss rod sets the relief. Turn it clockwise to pull the neck backward and reduce relief; anticlockwise to let the strings pull it forward and increase relief.
Never force a truss rod. A quarter turn, then let the neck settle for a few minutes before measuring again. A rod that is cranked hard can strip its threads or snap, and a snapped rod means removing the fretboard.
Measuring relief properly
Tune to pitch
Relief is measured with the strings at playing tension, in playing position. Measuring with the strings slack tells you nothing.
Capo the first fret
This removes the nut from the measurement so you are reading the neck, not the nut.
Fret the last fret
Now the string is a straight line between the first and last fret, and the gap at the middle is the relief.
Measure at the seventh fret
Slide feeler gauge blades under the string between the seventh and eighth frets until one just touches. That is your relief.
Adjust and re-measure
A quarter turn at a time, then measure again. Repeat until the reading is in range.
Action: what it is and where to measure it
Action is the gap between the top of a fret and the bottom of a string, measured at the twelfth fret. It is the measurement that decides how hard the guitar is to play, and it is the one players complain about when they say a guitar "fights them".
Action is set at two places: the nut, which controls the height of the strings over the first few frets, and the saddle or bridge, which controls the height further up the neck.
| Instrument | Relief at 7th | Action at 12th | Nut clearance at 1st |
|---|---|---|---|
| Electric | 0.15 – 0.20 mm | 1.2 – 1.6 mm | 0.25 – 0.4 mm |
| Steel-string acoustic | 0.20 – 0.25 mm | 2.0 – 2.8 mm | 0.3 – 0.5 mm |
| Classical | 0.25 – 0.35 mm | 3.0 – 4.0 mm | 0.4 – 0.6 mm |
| Bass | 0.25 – 0.35 mm | 2.0 – 3.0 mm | 0.4 – 0.6 mm |
The nut: where most playability problems live
A nut cut too high makes the first three or four frets hard to press and pulls them sharp. It is the single most common fault on a factory guitar, and it is invisible unless you measure for it.
Check it by pressing each string down at the third fret and looking at the gap between the string and the first fret. There should be a barely visible gap — a few thousandths of an inch. If you can see daylight, the slot is too high.
Nut slots only get deeper. Take a fraction off, test, and repeat. A slot that is one stroke too deep needs the whole nut replaced or shimmed.
The correct order
Fret level first
If the frets are not level, nothing you measure afterwards means anything.
Set the relief
Adjust the truss rod until the relief at the seventh fret is in range.
Set the nut height
Cut the slots so the first-fret clearance is right.
Set the saddle or bridge
Adjust until the action at the twelfth fret is where you want it.
Intonate last
Changing the saddle height changes the intonation. Adjust the saddle position only after the height is final.
Relief gives the string room. Action decides how hard you have to work. They are not the same adjustment, and doing them in the wrong order means doing them twice.
