Guitar Theory
Circle of Fifths
The circle of fifths is a map of all 12 musical keys arranged so that each key is a perfect 5th apart from its neighbors. It shows which keys share notes, which chords naturally follow each other, and how to navigate the harmonic landscape of Western music. Once you understand it, a lot of theory that seemed complicated becomes obvious.
The 12 keys arranged as a circle
Major keys above. Relative minor keys below each. Moving clockwise adds one sharp. Moving counterclockwise adds one flat.
Starting from C and moving clockwise, each key is a perfect 5th higher than the last: C, G, D, A, E, B, and so on. C major has no sharps or flats. G major has one sharp (F#). D major has two sharps (F#, C#). Each step clockwise adds exactly one sharp to the key signature.
Going counterclockwise from C adds flats instead. F major has one flat (Bb). Bb major has two flats. Each step adds one flat.
Relative minors
Every major key has a relative minor that shares the exact same notes. C major and A minor use the same seven notes. G major and E minor share the same notes. On the circle of fifths, the relative minor is listed just inside or below each major key.
This means knowing the circle also tells you every key's relative minor instantly. The relative minor is always the 6th degree of the major scale. In C major, count up six steps: C, D, E, F, G, A. A is the relative minor.
Closely related keys share the most notes
Keys that are adjacent on the circle differ by only one note. C major and G major share six of their seven notes. That closeness means transitioning between adjacent keys sounds smooth. The chords from one key mostly fit the other.
Keys on opposite sides of the circle share the fewest notes. C major and F# major share only one note. Moving from one to the other sounds like a major key change, which is why it is used for dramatic modulations.
The V-I relationship
Every key on the circle has its V chord one step clockwise. In C major, the V chord is G major. In G major, the V chord is D major. The circle visually shows why V resolves to I: they are the closest keys on the map, one fifth apart.
This is the foundation of diatonic harmony. The V-I resolution is the strongest move in Western music and the circle of fifths is a map of exactly that relationship repeated through all 12 keys.
How guitarists actually use it
Finding chords in a key
The I, IV, and V chords of any key are the three keys closest on the circle. C major's I-IV-V is C, F, G. All three are adjacent.
Transposing songs
If a song is in A and you want it in D, move two steps clockwise on the circle. Your chord shapes all shift by the same interval.
Understanding chord progressions
Most common progressions move counterclockwise on the circle (V to I, then to IV). The circle lets you see why those movements feel natural.
Modulation
Moving to an adjacent key on the circle is the smoothest modulation. Moving across the circle is the most dramatic. The circle shows the distance at a glance.
Guitar keys and the circle
On guitar, the open-string keys E, A, D, and G are all adjacent on the circle. That is not a coincidence. The standard tuning (E A D G B E) is built around fifths, the same interval the circle is based on. This is why so many guitar songs are in E, A, D, or G. Those keys align with the open strings and the natural resonance of the instrument.
Understanding the circle also helps when transposing. If you know a song in E and need it in A, the circle tells you they are two steps apart and helps you visualize what changes.
Explore any key on the fretboard
Pick any key from the circle and load it in the Scale Mapper to see every note and diatonic chord across the full neck.
Open Scale Mapper →