Circle of
5ths
When it comes to music theory, the circle of fifths is one of the most important concepts you can learn. Useful for notation, transposition, understanding key signatures, and familiarizing yourself with the general structure of music, it is well worth your time to add the circle of fifths to your vault of music theory knowledge. The circle of fifths can seem a little overwhelming at first, but you will soon realize how easy it really is to understand!
Deciphering the Circle
The circle of fifths is the relationship among the 12 tones of the chromatic scale, their corresponding key signatures, and the associated major and minor keys. Looking at the circle:

the outer section shows the actual key signatures

the capital letters represent the corresponding major keys

the lowercase letters represent the corresponding minor key
The Fifths
The reason it’s called the circle of fifths is because of the interval relationships between each key signature.
Let’s start at C Major and work our way clockwise.

G is a 5th up from C

D is a 5th up from G

A is a 5th up from D

E is a 5th up from A

and so on…
The same applies to the minor keys (on the inner circle). Let’s start with A Minor.

E is a 5th up from A

B is a 5th up from E

F# is a 5th up from B

C# is a 5th up from F#

and so on…
The Circle of Fourths?
Occasionally, someone will call the circle of fifths the “circle of fourths,” because if you move around the circle counterclockwise, you will see the progression moves by fourths. however this is much less common, and most refer to fifths.
Key Signatures
Because key signatures can get a little tricky to remember, the circle of fifths is a great tool! Let’s look at how the key signatures coordinate with the circle of fifths below:

C Major and A Minor have no sharps and no flats

G Major and E Minor have 1 sharp

D Major and B Minor have 2 sharps

A Major and F# Minor have 3 sharps

and so on…