Circle of fifths

In music theory, the circle of fifths is a way of organizing pitches as a sequence of perfect fifths. Starting on a C, and using the standard system of tuning for Western music (12-tone equal temperament), the sequence is: C, G, D, A, E, B, F♯ (G♭), C♯ (D♭), G♯ (A♭), D♯ (E♭), A♯ (B♭), E♯ (F), C. This order places the most closely related key signatures adjacent to one another. It is usually illustrated in the form of a circle.

Twelve-tone equal temperament tuning divides each octave into twelve equivalent semitones, and the circle of fifths leads to a C seven octaves above the starting point. If the fifths are tuned with an exact ratio of 3:2 (the system of tuning known as just intonation), this is not the case (the circle does not "close").