The guitar is a transposing instrument. Its pitch sounds one octave lower than it is notated.
A variety of different tunings are used. The most common by far, known as "Standard Tuning" (EADGBE), is as follows:
* sixth (lowest tone) string: E (a minor thirteenth below middle C—82.4 Hz)
* fifth string: A (a minor tenth below middle C—110 Hz)
* fourth string: d (a minor seventh below middle C—146.8 Hz)
* third string: g (a perfect fourth below middle C—196.0 Hz)
* second string: b (a minor second below middle C—246.92 Hz)
* first (highest tone) string: e' (a major third above middle C—329.6 Hz)
A guitar using this tuning can tune to itself by the fact, with a single exception, that the 5th fret on one string is the same note as the next open string; that is, a 5th-fret note on the sixth string is the same note as the open fifth string. The exception to this rule is the interval between the second and third strings, in which the 4th-fret note on the third string is equivalent to the open second string.
Standard tuning has evolved to provide a good compromise between simple fingering for many chords and the ability to play common scales with minimal left hand movement. There are also a variety of commonly used alternate tunings - most of which are chord voicings that can be played on open strings or made by moving the capo.
Many guitarists use a long established (centuries old) tuning variation where the lowest string is 'dropped' two semi-tones down. Known as Drop-D (or dropped D) tuning it is, from low to high, DAdgbe'. This allows for open string tonic and dominant basses in the keys of D and D minor. It also enables simple fifths (powerchords) to be easily played without the need for a high technical skill level. Many contemporary rock bands downtune the entire tuning by several semi-tones, making, for example, Drop-C or Drop-B tunings, However this terminology is inconsistent with that of "drop-D" as "drop-D" refers to dropping a single string to the named pitch. Often these new tunings are also simply referred to as the "Standard" of the note in question e.g. - "D Standard" (DGCFAD). Many other open tunings, where all of the strings are tuned to a similar note or chord, are popular for slide guitar playing.
As with all stringed instruments a large number of scordatura are possible on the guitar.