Classical guitar action height
Nylon strings swing in a wider arc than steel, so a classical guitar needs more room above the frets. StewMac's suggested setup is 5/32″ (3.96 mm) on the 6th string and 1/8″ (3.17 mm) on the 1st, measured at the 12th fret, with just 0.002″ (0.05 mm) of neck relief and, at the 1st fret, 0.030″ (0.76 mm) under the 6th string and 0.024″ (0.61 mm) under the 1st.
Classical guitar action, StewMac
6th and 1st string at the 12th fret, neck relief and nut height from StewMac's suggested settings.
| Instrument | Low (mm) | High (mm) | Relief (mm) | Fret |
|---|---|---|---|---|
| Classical guitar | 4.0 | 3.2 | 0.1 | 12 |
StewMac — String Action Gauge Instructions (Suggested action settings)
How to use it
- With the guitar at pitch, slide a steel rule or action gauge under the 6th string at the 12th fret, then under the 1st, and note both gaps.
- Enter both readings; the 650 mm scale is already filled in.
- Loosen the strings, pull the saddle out of its slot and sand the bottom by the amount shown. Put it back, tune and measure again.
Help and explanations
Treat them as a starting point. Players with a light touch often go a little lower; flamenco guitars are traditionally set lower still and accept a little buzz as part of the sound.
Sanding the saddle
The saddle of a classical guitar sits loose in the bridge slot, held only by string pressure, so it lifts out once the strings are slack. The 12th fret is halfway along the 650 mm scale, so action there changes by half of the saddle move. A guitar measuring 4.6 mm on the 6th and 3.6 mm on the 1st needs about 1.3 mm off the bass end of the saddle and 0.9 mm off the treble end to reach StewMac's 3.96 and 3.17 mm.
Draw the line with a pencil, sand on flat paper and keep the bottom square. Took off too much? A thin shim of bone or hardwood under the saddle brings it back.
Truss rod or no truss rod
Many classical guitars are built without an adjustable truss rod. If yours has one, the adjuster is usually reached through the soundhole or at the headstock: tighten to reduce relief, loosen to add it, a small fraction of a turn at a time. Without a rod, relief can't be adjusted at home; a neck bowed well past 0.05 mm needs a luthier, not a lower saddle.
Check the nut as well. More than 0.76 mm (0.030″) under the 6th string or 0.61 mm (0.024″) under the 1st, at the 1st fret, makes first-position chords stiff and pulls them sharp, however good the action is at the 12th.
Tips
- Nylon trebles go sharp easily at the 12th fret: after saddle work, compare fretted and harmonic notes with the intonation checker.
- Normal and hard tension sets feel different at the same action; compare them in the string tension calculator.
- Making a new nut or saddle? Classical guitar string spacing places each string.
Frequently asked questions
What is the standard action on a classical guitar?
StewMac suggests 5/32″ (3.96 mm) on the 6th string and 1/8″ (3.17 mm) on the 1st, measured at the 12th fret.
Why is classical guitar action higher than on an acoustic?
Nylon vibrates in a wider arc at lower tension. A steel-string Martin is set at 2.03–2.29 mm on the low E; a classical needs about 4 mm to avoid buzz.
How much do I sand the saddle of a classical guitar?
Twice the change you want at the 12th fret. To go from 4.6 to 3.96 mm on the 6th string, take about 1.3 mm off the bass end.
Does a classical guitar have a truss rod?
Many don't. Look through the soundhole at the end of the fingerboard and on the headstock, just behind the nut; if there's no adjuster, relief can only be fixed at the bench.
How high should the strings be at the 1st fret?
StewMac gives 0.030″ (0.76 mm) under the 6th string and 0.024″ (0.61 mm) under the 1st, from the top of the 1st fret to the underside of the open string.