G, also called Sol or So, is the fifth note of the fixed-do solfège starting on C. It is the fifth note and the eighth semitone of the solfège.
As such it is the dominant, a perfect fifth above C or perfect fourth below C. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of middle G (G4) note is approximately 391.995 Hz.
[1] See pitch for a discussion of historical variations in frequency.
It has enharmonic equivalents of F (F-double sharp) and A (A-double flat).
In the medieval period the musical note G was known as gesolreut within the Guidonian hand hexachord system.