A guitar's string height, called the action, is one of the most important factors affecting playability. An action that is too high makes playing heavy, while one that is too low causes buzzing. This LG Guitar Guide article explains what action means, how it is measured and which parts of the instrument affect it.
What action means
Action means the distance of the string from the frets on the fretboard. In practice it is measured as the height between the underside of the string and the top edge of the fret, usually at the upper frets of the neck. The greater this distance, the more force pressing the string requires. On a classical guitar the action is typically a little higher than on a steel-string, because nylon strings vibrate in a wider arc and a low setup would cause buzzing more readily.
How action is measured
Action can be measured with a thin ruler marked in millimetres. The measurement is usually taken at the twelfth fret, from the underside of the string to the top of the fret. The action on the bass side, the thicker strings, is naturally a little higher than on the treble side. Exact universal figures are hard to give, because the suitable height depends on playing style and instrument, but measuring your own instrument gives a reference point and reveals if something is clearly off.
Too high or too low a setup
A too high action is recognised by the strings requiring a lot of force to press, especially past the middle of the neck, so that the left hand tires quickly. Playing feels laborious and intonation can suffer when the string has to be stretched as it is pressed. A too low action, in turn, causes buzzing when the vibrating string strikes the frets. The right setup is a compromise: as low as possible for effortless playing, but high enough that no buzzing occurs at a normal playing force.
Saddle, nut and neck
Three parts above all affect the action. The nut, at the top of the neck, determines the string height at the lowest frets. The saddle, in the bridge, determines the height at the upper frets, and shaping it is the most common way to adjust the action. The angle of the neck and any curvature affect the whole length of the neck. A classical guitar usually does not have the adjustable truss rod of a steel-string guitar, so the adjustment is made mainly by working the nut and saddle.
When to turn to a professional
Lowering the saddle is an irreversible step: material can be removed but not added back. An experienced player can carefully make a small lowering, but if the height is clearly off, the neck has unusual curvature or the instrument buzzes in several places, it is worth turning to a competent repairer. A well-done setup changes the playing experience significantly and is often an inexpensive way to improve an existing instrument.
Summary
The action decides whether an instrument feels effortless or heavy. Measuring your own instrument's height and understanding which parts affect it help you recognise when a setup is needed and when it is best left to a professional.
