Circle Of 5ths Describes the pattern of scales going through the 13 different keys. Starting with C Scale (no sharps or flats) it goes up 5 notes in the scale to reach the next scale. Each time it adds one sharp in the order of sharps (FCGDAEB). Flats start with C Scale and go down 5 notes in the scale to reach the next scale. Each time it adds one flat in the order of flats (BEADGCF). Download Circle of 5ths (below) and Circle of 5ths Explained for reference.
