G as a Scale Degree

G is the fifth degree of the C major scale, called Sol in movable-doh solfège, and the perfect fifth it forms with the tonic C is, alongside the octave, the most consonant interval available in Western tonal harmony, which is why the dominant chord built on the fifth degree carries such strong pull back toward the tonic in standard tonal composition. G major is also one of the most commonly used keys for instruments tuned around open strings, since several standard orchestral and folk string instruments include a G string among their open pitches.

The circle of fifths, the standard theoretical device for organising the twelve pitches and their key signatures by successive fifths, takes its name from exactly this interval, and G major, one fifth removed from C major in the sharp direction, sits as the very first step away from C on that circle, making it among the most closely related keys to C in conventional tonal harmony.