Guitar chord for chords having their root note on the third, fourth, fifth, and sixth strings. For a six-string guitar in standard tuning, it may be necessary to drop or omit one or more tones from the chord; this is typically the root or fifth. The layout of notes on the fretboard in standard tuning often forces guitarists to permute the tonal order of notes in a chord. The playing of conventional chords is simplified by open tunings, which are especially popular in folk, blues guitar and non-Spanish classical guitar (such as English and Russian guitar). For example, the typical twelve-bar blues
Guitar frets, which are metal strips (usually nickel alloy or stainless steel) embedded along the fretboard and located at exact points that divide the scale length in accordance with a specific mathematical formula. The exceptions include fretless bass guitars and very rare fretless guitars. Pressing a string against a fret determines the strings' vibrating length and therefore its resultant pitch. The pitch of each consecutive fret is defined at a half-step interval on the chromatic scale. Standard classical guitars have 19 frets and electric guitars between 21 and 24 frets, although guitars have been made with as many as 27 frets.