Circle of fifths

A circular diagram arranging the twelve pitch classes by perfect fifths. It shows relationships among major and minor keys, including their key signatures and relative-key pairs.

Perfect fifth: A musical interval spanning seven semitones in twelve-tone equal temperament. Each step around the circle advances by this interval.
Major key: A musical key organized around a major scale and its tonic. The outer ring commonly places major keys in fifth-step order.
Roman numeral analysis: A system that labels chords by scale degree using Roman numerals. Key context supplied by the circle helps identify each chord's scale-degree function.
Chromatic circle: A circular arrangement of the twelve pitch classes in semitone order. It orders pitches by adjacent semitones rather than by perfect fifths.
Pitch class: A set of pitches separated by one or more octaves, treated as equivalent. The circle orders the twelve pitch classes rather than particular registers.
Minor key: A musical key organized around a minor scale and its tonic. The inner ring commonly aligns each minor key with its relative major.
Transposition: The process of shifting a musical passage to a different pitch level. Moving around the circle provides a systematic way to compare transposed keys.
Fifths tuning: A tuning approach that derives pitches through a chain of perfect fifths. Unlike a diagram, it describes a tuning procedure and its resulting pitch relationships.
Key signature: A notation showing which notes are consistently sharpened or flattened in a musical key. The circle's positions correspond to the sharps or flats used by each key.
Relative key: One of two keys that share a key signature but have different tonics and modes. Neighboring inner and outer entries show these key pairs.

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