What Is the Proper String Action for an Acoustic Guitar?
An Explanation of the Correct Measurement Method, Causes of Excessive String Action, and How to Adjust It

The general recommended string action for an acoustic guitar is approximately 2.5 mm on the 6th string and approximately 2.0 mm on the 1st string at the 12th fret. Many guitars come from the factory set to values around these figures to accommodate a wide range of playing styles. Since the bass strings are thicker and have a larger amplitude of vibration, they are generally set slightly higher than the treble strings.

However, these figures are merely “guidelines,” and the optimal string height varies depending on the player’s style. For example, for players who use a pick to strum forcefully, setting the string height slightly higher—around 2.6 mm to 2.8 mm on the 6th string—is recommended, as a string height that is too low can cause the strings to hit the frets and produce unpleasant noise (buzz).On the other hand, for solo guitarists who primarily use fingerstyle (fingerpicking) or players who frequently use complex chord changes, the string height may be set lower—to around 2.0 mm to 2.2 mm on the 6th string—to prioritize ease of fingering. Fine-tuning the string height to suit your own style is the fastest way to improve.

To measure string height accurately, use a dedicated “string action gauge” or a “straightedge” with a scale that starts at zero at one end. Standard plastic rulers are not suitable for accurate measurements because they have extra space at the ends.

The measurement procedure is as follows.

1. Hold the guitar as you would when playing it (if the guitar is laid flat, the force on the neck changes due to gravity, which may prevent an accurate measurement).

2. Place the ruler perpendicular to the top of the metal bar (fret wire) at the 12th fret.

3. Align your line of sight so that it is perfectly horizontal at the point where the string and the ruler intersect.

4. Read the measurement from the “top” of the fret to the “lowest point (bottom)” of the string.

If your line of sight is shifted upward or downward, an optical illusion can easily cause an error of about 0.5 mm. Additionally, if you want to eliminate the influence of the height at the nut and check the pure condition of the neck and saddle, there is a technique used by professional repair technicians: measure the string height at the 12th fret with a capo attached to the 1st fret.

The biggest drawback of excessive string action is that “it requires excessive force to press down the strings.” Especially when playing barre chords like the F chord, the distance you have to push the string down to the fret increases, so you may not be able to press it down firmly enough with just your finger strength—resulting in the note not sounding—or your fingertips may start to hurt quickly. This is a major reason why beginners give up.

Another issue that’s often overlooked is “pitch inaccuracy.”When you press down on a guitar string, the same physical process occurs as when you bend the string toward the fretboard. The higher the string action, the farther you have to press the string down, which applies extra tension. As a result, even if you tune the open strings accurately with a tuner, the notes will sound sharp (higher than they should) when you press down on the higher frets. If you notice that the sound becomes muddy, especially when playing chords in the higher positions, it’s highly likely that high string action is the cause.

On the other hand, having the string height set too low also causes serious problems. The most common issue is “fret buzz.” When a string is plucked, it vibrates widely in an elliptical pattern. If the string height is too low, the vibrating string will come into contact with an adjacent fret, producing an unpleasant metallic sound such as a “zing” or a “buzz.”

Furthermore, the acoustic impact cannot be ignored. The volume of an acoustic guitar is produced when the vibration of the strings is transmitted through the saddle on the bridge to the top (soundboard), causing the entire body to resonate. If the string height is too low, the downward pressure (tension) exerted by the strings on the saddle weakens, preventing the top from vibrating sufficiently.As a result, the tone loses its brightness and sustain, resulting in a flat, lackluster sound. Lowering the string height excessively in pursuit of playability leads to sacrificing the rich, natural resonance that is characteristic of an acoustic guitar.

Staff Comment

Even though we simply call them “acoustic guitars,” your options vary greatly depending on your playing genre and the sound you want to achieve!
Each one is packed with elements that, once you get hooked, you won’t be able to resist—it’s a lot of fun!
If you’re just vaguely thinking, “I’d like to try playing an acoustic guitar,” I recommend starting with a folk guitar!

The most common cause is “forward bow” of the neck. This refers to a condition where the strong tension of the strings pulls the neck into an arch toward the strings, causing it to curve. When forward bow occurs, the string height becomes extremely high, particularly from the middle of the neck (around the 5th to 7th frets) up to the 12th fret. To check for this, press down on the 1st fret and the top fret simultaneously, and look at the gap between the string and the fret in the middle (around the 7th fret).A gap about the width of one or two postcards is normal, but if the gap is wider than that, the neck is bowing forward.

Additionally, “neck lift” is a condition commonly seen in older guitars that have been subjected to strong tension over a long period. This is not a warping of the entire neck, but rather a condition where the entire neck lifts up from the joint with the body (usually around the 14th fret). Neck lift is difficult to correct with standard adjustments and requires specialized, extensive repairs.

An incorrect saddle height can also be a cause. With new guitars—especially entry-level models in the low- to mid-price range—the saddle is often set higher than usual so that players can file it down to their preferred height after purchase.

In addition, “climate changes (fluctuations in humidity)” caused by Japan’s four seasons directly affect string action. Wood has the property of absorbing and releasing moisture from the surrounding environment. When humidity rises from the rainy season through the summer, the wood absorbs moisture and expands, causing the entire body to swell and raising the string action. Conversely, during the dry winter months, the wood contracts, and string action tends to drop. This is why the feel of the guitar changes during seasonal transitions.

A symptom unique to acoustic guitars is the bulging of the top. The top around the bridge is made of thin wood, only a few millimeters thick, and is constantly being pulled upward by the strings. If the strings are left on the guitar for many years or if the instrument is left in a high-humidity environment, the wood can no longer withstand the tension, and the area behind the bridge will bulge outward.

When the top bulges, the entire bridge and saddle assembly is lifted along with it, resulting in significantly higher string action. If you place a straight object—such as the edge of a ruler—against the top of the body behind the bridge and notice a gap or wobbling like a seesaw, this is evidence that the top has bulged.

If the cause of the high string action is “neck bow,” you can adjust it by turning the metal rod—the “truss rod”—embedded inside the neck. Insert a special wrench into the hex socket located near the soundhole or the headstock and turn it.

To correct forward bow, turn the truss rod “clockwise” to tighten it. The most important precaution here is to limit each turn to “45 degrees (1/8 turn) to a maximum of 90 degrees (1/4 turn).” After turning the rod, allow some time for the neck to settle; then retune the guitar and check the bow again.

If you force it too hard, you risk causing catastrophic damage, such as the truss rod breaking inside the neck or the fingerboard peeling off. If it’s too tight to turn, never force it any further.

If the string action remains high even when the neck is nearly straight, shave down the bottom surface of the “saddle” resting on the bridge to lower the height. Keep in mind the following calculation: if you want to lower the string action at the 12th fret by 0.5 mm, you’ll need to shave 1.0 mm—twice that amount—from the bottom of the saddle.

To perform this task, attach sandpaper to a “completely flat surface” such as a glass plate or marble, and sand the underside of the saddle evenly while keeping it at a right angle. If you sand even slightly at an angle or the underside becomes wavy, the string vibrations won’t be transmitted correctly to the bridge, resulting in a loss of sustain.This is especially true for Electric Acoustic guitars, where the tightness of the contact between the saddle and the bridge directly affects the volume balance; even the slightest under-sanding can lead to problems where only certain strings produce no sound through the amplifier. Since oversanding is irreversible, this is a task that requires patience: draw a guideline with a pencil to indicate how much to sand, sand a little, reinstall the saddle on the guitar, restring it, and check the sound.

If the truss rod is tightened to its limit, or if you notice a warped neck heel or severe bulging of the top, it is impossible to adjust the guitar on your own. Repairing these issues requires major repairs, such as a “neck reset”—where the neck is temporarily removed from the body to readjust its angle—or straightening the top.Such repairs are often expensive, ranging from tens of thousands to over a hundred thousand yen, and in the case of entry-level guitars, the repair costs frequently exceed the instrument’s original purchase price.

If your current guitar is difficult to adjust on your own and you’re struggling to justify the repair costs, it may be a wise choice to let it go and upgrade to a higher-end guitar that’s already set up for comfortable playing right from the start. If you’d like to know the value of an instrument you no longer need, consider using a buyback service or similar option to request an appraisal that takes its current condition into account—this will provide you with the best basis for deciding on your next step.

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Staff Comment

When choosing an acoustic guitar, the time spent considering specifications like materials and body shapes can be both frustrating and fun!
The information above is merely a general trend; there’s no rule stating that a guitar “can’t be used for this genre” or “isn’t suitable.”
Don’t overthink it—it’s perfectly fine to start by picking up a guitar that catches your eye!

Author: Mochizuki (Advance Guitars Staff)

In my personal life, I mainly play electric guitar. Drawing on my boundless love and interest in instruments—so much so that I continue playing guitar even during work breaks—I share the appeal of acoustic guitars using some of the finest strumming techniques at Advance Guitars.

Qualifications and Experience: 4 years as a musical instrument appraiser

▶︎Read my articles here:
The Secrets of the Ovation Adamas
The Legend of Terry Nakamoto: Yamaha’s Four Heavenly Kings